Radiation Monitoring Systems - Fuji Electric · PDF file · 2011-03-20Radiation...

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Radiation Monitoring Systems

Highly accurate and reliable equipment useful to our customers

Whole body counter that measures internal contamination levels

Sample rack that tests for the emission of radioactive material

Detector that measures neutron dose rates

Body surface monitor that measures body surface contamination levels

Detector that measures gamma-ray dose ratesPersonal dosemeter that measures external radiation exposure

Fuji Electric actively develops various types of essential radiation measuring instruments and computer systems to contribute to the safety control of nuclear power plants and other facilities that use radiation.

Fuji Electric’s Radiation Control Systems

Environmental radiation measurements

Personal dose measurements

Cover photo:Because certain types of radia-

tion, such as that used in X-raymachines for example, exhibitstrong penetrating power and be-cause the generated radioactiverays do not change even when sub-jected to heat or chemical treat-ments, radiation technology iswidely used in the fields of medi-cine, pharmaceuticals and ironmanufacturing, and at various re-search facilities. Although radioac-tive material is generated as abyproduct from nuclear facilities, asin the case of above-mentioned fa-cilities that use radiation, appropri-ate controls are implemented to pre-vent adverse affects on humans.

In these fields, Fuji Electric iscontributing positively to society bydeveloping and supplying radiationmonitoring devices and systemssuch as personal dosemeters to pro-tect personal health and radiationmonitors for ensuring environmen-tal safety.

The cover photo illustrates theharmonious coexistence betweenfacilities that use or require the con-trol of radiation and their surround-ing environment.

Head Office : No.11-2, Osaki 1-chome, Shinagawa-ku, Tokyo 141-0032, Japan

Radiation Monitoring Systems

CONTENTS

Current Trends in Radiation Monitoring Systems 100

Personal Dose Monitoring System 102

Environmental Radiation Monitoring System 109

Environmental Radiation Measuring Equipment 114

Radioactive Contamination Monitors 118

Industrial Measurement Instruments that Use Radioisotopes 126

Vol. 50 No. 4 FUJI ELECTRIC REVIEW100

Etsuo Kono

Current Trends inRadiation Monitoring Systems

1. Introduction

During the more than 100 years since the discov-ery of X-rays in 1895 by the German scientist Roent-gen, the use of radiation has been advanced inscientific, engineering and medical fields. The radia-tion measurement technology applied in industrialapplications mainly utilizes the material penetrationcapability of radiation rays and is incorporated intoproduction lines for iron and steel, paper, film, etc.,where the technology is used in thickness gauges orcast-iron level gauges to measure the thickness or fluidlevel of an object rapidly, with high precision andwithout contact. In recent years, due to the overseasmigration of iron/steel and chemical fiber productionand the absence of an increase in production quanti-ties, including the portion produced overseas, demandfor measuring instruments that utilize radiation tech-nology has continued on a downward trend.

On the other hand, radiation monitors are beingshipped to facilities that use radioisotopes such asnuclear power plants, nuclear-related research organi-zations and universities, hospitals and pharmaceuticalcompanies. When nuclear power facilities first beganto be constructed, there was an increase in demand forradiation monitoring equipment, which gradually be-came the largest sector of the market for radiationequipment. Hospitals promoted the installation ofdiagnostic radiology equipment, and accompanying theuse and control of medical isotopes that are adminis-tered to patients, radioactive wastewater treatmentfacilities and radiation monitoring equipment werealso promoted.

Figure 1 shows the historical and future estimatedproduction of radiation measuring instruments madeby the Japan Electric Measuring Instruments Manu-facturers’ Association (JEMIMA). Demand for radia-tion monitors is largely dependent upon plans for thenew construction of nuclear power plants, and thedelay in construction planning effects the size of themarket.

2. Current Status of Radiation MonitoringSystems

Radiation monitors fall into the categories ofenvironmental radiation monitoring, personal dosemonitoring, surface contamination monitoring, radio-active material monitoring and area process monitor-ing.

Environmental radiation monitoring measures thespatial gamma-ray dose rate, the concentration ofgaseous radioactive material, and the concentration ofairborne radioactive material. Measurement of thespatial gamma-ray dose rate is implemented with alow range (background dose rate to 10 µSv/h range)monitor and a high range (10 µSv/h to 10 mSv/h range)

Fig.1 Production of radiation measuring instruments: historicaloutput and future projections

200

150

100

50

0

250

Pro

duct

ion

ou

tpu

t (1

00 m

illi

on y

en)

’ 93

11

25

32

149

’ 94

10

28

27

149

’ 95

11

30

37

133

’ 96

9

29

32

136

’ 97

8

29

37

117

’ 98

13

26

21

110

’ 99

21

21

20

132

’ 00

(Fiscal year)

18

20

21

136

’ 01

25

16

22

142

’ 02

18

13

17

108

’ 03

20

14

18

123

’ 04Future

projections

18

14

19

115

’ 05

18

15

18

110

’ 06

20

15

17

120

’ 07

20

16

17

130

Integrated devicesRadiation monitorInstrument utilizing radiation technologyOther

Current Trends in Radiation Monitoring Systems 101

monitor. NaI (Tl) scintillation detectors and sphericalpressurized ionization chambers are used as radiationdetectors. Radioisotope diagnostic radiology equip-ment is increasingly being used for in-hospital screen-ings, and monitor readings have a greater chance tofluctuate when, for example, a patient who has beeninternally administered a radioisotope approaches theenvironmental monitoring equipment or when a cartthat transports radioactive elements passes nearby.Recently, low range monitors are being provided withthe capability to measure spectral energy, and spatialgamma-ray equipment is increasingly being used toenable identification of the radiation source in caseswhen there is an unexpected change in the readingunder normal measurement conditions. In combina-tion with this function, energy characteristic compen-sation is being implemented with a digital method ofenergy load correction having good counting accuracy.

For the environmental dosimetry performed bothon-site and off-site by fixed-point continuous gamma-ray monitoring, a transition is underway from passivedosemeters, such as a thermoluminescence dosemeterin which measuring-related processing such as theheating of an element is required, to electronic doseme-ters capable of recording the history of dosage changesover time.

For personal dose monitoring, electronic doseme-ters capable of measuring gamma-rays, beta-rays andneutrons are utilized in practical applications formeasuring external exposure to radiation and arebeing used to record the doses. In particular, gamma-ray and beta-ray dosimetry will changeover to electron-ic dosemeters in the near future. Communicationbetween the dosemeter and dose reader is graduallytransitioning from infrared communication to wirelesscommunication, and short-range communications tech-nology is enabling data communication to be imple-mented with a dosemeter carried in a work clothespocket or the like.

Surface contamination monitoring of a physicalobject is implemented by whole body surface monitors,article monitors, laundry monitors and the like. Plas-tic scintillation detectors for detecting beta-rays areused as radiation detectors because they are capable of

measuring a large area within a short time interval.For the dust monitors used in area process moni-

toring, a single radiation detector capable of detectingboth beta-rays and alpha-rays, simultaneously andindividually, is being used, making it possible to lessenthe influence of radiation emitted from natural radio-isotopes such as radon/thoron daughters. In facilitiesthat handle nuclear fuel, large-area semiconductordetectors capable of discriminating alpha-ray energyare used, and dust monitors capable of measuringplutonium separation are being installed.

3. Technical Trends

Radiation monitoring equipment must be highlyreliable. Technical development for the future istargeting smaller sizes, lighter weight, lower cost,longer useful life and even higher reliability.

Passive radiation detectors and finite-life radiationdetectors such gas-filled counters and the like will bereplaced with smaller-size and lighter weight semicon-ductor detectors. Because the silicon semiconductormaterial in a semiconductor element operates stably atroom temperature and possess components similar tohuman body tissue, semiconductor elements are suit-able for dosimetry and will continue to be used as themain element in future radiation detectors.

Construction of nuclear fuel reprocessing facilitiesand accelerator facilities is advancing and neutrondosimetry is crucially important at these facilities.Because at accelerator facilities, in particular, theneutron energy to be measured exceeds 10 MeV, devel-opment work is progressing for a new type of neutrondetector, such as one in which material that boostssensitivity of the neutron detector, which otherwisetends to decrease at high energy levels, is added to aconventional moderator.

4. Conclusion

Fuji Electric intends to develop commercial radia-tion monitoring equipment that uses mainly semicon-ductor radiation detectors and is optimally suited forvarious measurement conditions.


Kei AoyamaOsamu UedaTakeshi Kawamura

Personal Dose Monitoring System

1. Introduction

The level of radiation safety control in the nuclearpower field and at facilities that utilize radiation hasbecome stricter with the revision of the radiationprotection regulations in April 2001 which incorporatethe recommendations of the International Commissionon Radiological Protection (ICRP Pub. 60) and thestipulation of a maximum exposure of 100 mSv/ 5 yearsin addition to the existing personal exposure dose limitof 50 mSv/year.

Since 2001, fluoroglass dosemeters and OSL (opti-cally stimulated luminescence) dosemeters have re-placed the conventional film badge as the personaldosemeters used in dose control. However, since thevalues measured by these dosemeters cannot be readdirectly, electronic dosemeters which permit the directread-out of dose values and are equipped with analarm function are recently being utilized for dosecontrol.

Overseas, the usage of electronic personal doseme-ters is also increasing, and an IEC standard has beenestablished for electronic dosemeters capable of mea-suring gamma rays, beta rays and neutrons.

The Japanese domestic standard for electronicpersonal dosemeters achieved conformance with theIEC standard in 2002, and JIS Z 4312 “electronicpersonal dose (rate) meter for X-rays, gamma rays,beta rays and neutrons” was revised.

In 1980, Fuji Electric developed an alarm-equippeddosemeter that uses a semiconductor detector, andsince then has continued to improve its dosemetertechnology. Fuji Electric’s personal dose control sys-tem, which increases the functionality of this electronicdosemeter and incorporates an area access controlapparatus, has garnered an approximate 70 % share ofthe market among Japanese domestic nuclear powerfacilities.

2. System Overview

With Fuji Electric’s personal dose monitoring sys-tem, a worker carries an electronic dosemeter whenentering a controlled area for radiation such as a

nuclear power plant, and the radiation dose receivedwhile the worker performs his or her task is measured.Upon leaving the controlled area, an area accesscontrol apparatus reads the dose data and a computersystem manages the dose per worker and dose pertask. Figure 1 shows an overview of this system. Inthe figure, the term “dosemeter” is used an abbrevia-tion for “electronic dosemeter.”

3. Electronic Dosemeter

An electronic dosemeter carried in a worker’spocket measures and displays in real time the amountof radiation received while the worker performs his orher task. This dosimeter is also equipped with afunction that issues an alarm in cases where theexposure dosage exceeds a preset value. A siliconsemiconductor detector that features a small size andlow power consumption is used as the sensor.

Passive dosemeters such as film badges, which arecharacterized by a simple construction, and highdurability and reliability, have previously been usedwidely as personal dosemeters. However, these pas-sive dosemeters were disadvantageous because theydid not permit the dose data to be read directly andbecause the process of obtaining monthly cumulativedose data was time consuming. Consequently, innuclear power plants in Japan, concurrent with theusage of passive dosemeters, electronic dosemeters(equipped with an alarm function) were also used tomonitor the dosage during work.

The development of electronic dosemeters hasmade progress in recent years, noise immunity andmechanical shock resistance have been enhanced,reliability improved, and the capability of measuringnot only X-rays and gamma rays, but also beta raysand neutrons, has been realized. Additionally, thedata communication capability provided with an elec-tronic dosemeter enables easy connection to an exter-nal data processing system by means of infrared orwireless communications, enabling the configuration ofa highly functional system for implementing rapidmeasurement archiving control, area access control,trend data measurement, and the like.


Main features of electronic dosemeters are summa-rized below.(1) Simultaneous measurement of multiple types of

raysX-rays, gamma rays, beta rays and neutrons can

all be measured simultaneously (for the first time inthe world).(2) Good data reliability

Performance is equivalent to that of a conventionalstatutory dosemeter (passive dosemeter). Data reli-ability was confirmed by evaluating measurement dataduring concurrent use at actual nuclear power plants.(3) Conformance with international standards

The International Electrotechnical Commission

(IEC) standard (IEC 61526) and the Japanese domesticstandard (JIS Z 4312) for electronic dosemeters areboth satisfied.

Fig.1 Overview of personal dose monitoring system

Fig.2 Gamma-beta dosemeter Table 1 Specifications of the gamma-beta dosemeter

ID card

Dosemeter

ID card

Dosemeter

ID card

Dosemeter

APD

APD

Area access control apparatus

Area access control apparatus

Dosemeter storage rack

Dosemeterstorage

Automation ofdose checking

Wireless communication with the dosemeter in the worker’s pocket

Work area

The control area

Inputting workinformation

Data communication while carried in a worker’s pocket

Wirelesscommunication

Inside the controlled area Outside the controlled area

Computer systemServer

Entering

Borrowinga dosemeter

Returninga dosemeter

Leaving

Work

10 cm

Dosemeter

Dosemeter

Dosemeter model NRN64311

Detector Semiconductor

Radiation detected Gamma (X) rays Beta rays

Energy range 50 keV to 6 MeV 300 keV to 2.3 MeV

Energy response ±20 %,137Cs standard

±30 %,90 Sr/ 90 Y standard

Angular response

±15 %,Up to 60°

vertically and horizontally,

137Cs standard

±30 %,Up to 60°


90 Sr / 90 Y standard

Indication range 0 to 999.99 mSv 0 to 999.9 mSv

Accuracy of indication

±10 %,0.1 to 999.9 mSv

±15 %,0.1 to 999.9 mSv

Alarm Sound level: 100 dB or greater, Display lamp: flashing LED (red)

Communication method Wireless (LF) and point contact

Power suppliesNiCd rechargeable battery

(providing power for 12 or more hours of continuous operation)

Ambient temperature 0 to 50°C

Size 110×57×17 (mm)

Mass 120 g


(4) Wireless communication improves operability andshortens processing time

Data transfers between the electronic dosemeterand the area access control apparatus are implementedvia wireless communication. Because data transferscan be implemented even while the dosemeter remainsinside one’s pocket, area access operability can beimproved and processing time shortened.

Recently, some systems are being realized in whichthis wireless communication function is expanded toachieve remote wireless monitoring capability.

With the goals of streamlining dose control andreducing the burden on workers, control at manynuclear power plants in Japan is transition toward theuse of only a single electronic dosemeter. The gamma(X) ray and beta ray dosemeter (hereafter referred toas the gamma-beta dosemeter) and the gamma (X) rayand neutron dosemeter (hereafter referred to as thegamma-neutron dosemeter) developed in response tothese trends are described below.

Fig.4 Gamma (X) ray angular response

Fig.3 Gamma (X) ray energy response Fig.5 Beta ray energy response

Fig.6 Beta ray angular response

3.1 Gamma-beta dosemeterThe gamma-beta dosemeter is equipped with two

sensors, one for detecting gamma (X) rays and theother for detecting beta rays, enabling both types ofradioactive rays to be counted simultaneously. Thegamma-beta dosemeter is shown in Fig. 2 and its mainspecifications are listed in Table 1.

The gamma ray sensor is sealed in a ceramicpackage in order to improve the environmental immu-nity of its silicon sensor chip, and is provided withenergy filters made of various types of metal to correctthe energy response according to the direction ofincidence (sensitive differs according to the gamma rayenergy). Energy response is shown in Fig. 3 andangular responses are shown in Fig. 4.

Because beta rays have low penetrating power andcan be stopped by a single aluminum substrate, thebeta ray sensor is housed in a ceramic package made ofresin film having a thickness of several tens of micronsin the direction of incidence. Energy response is shown

Rel

ativ

e re

spon

se (

137 C

s st

anda

rd)

Gamma ray energy (MeV)

0.10.01 1 10

0.2

0

0.4

0.6

0.8

1.0

1.2

1.4

±30 % 60 keV to1.5 MeV

JIS standard(EP2 type)

±20 %50 keV to

6 MeV(product

specification)

20 %

10 %

-10 %

-30 %

-40 %

-50 %

-60 %

0 %

-20 %

20 %

10 %

-10 %

-20 %

-30 %

-40 %

-50 %

-60 %

0 %

Reference0°

15° below30° below

45° below

60° below

75° below

90° below

15° above30° above

45° above

60° above

75° above

90° above

Reference0°

15° left30° left

45° left

60° left

75° left

90° left

15° right30° right

45° right

60° right

75° right

90° right

Left Right

(b) Gamma ray angular response (137Cs, left and right)

(a) Gamma ray angular response (137Cs, above and below)

Below

Above

10.1 10

0.2

0

0.4

0.6

0.8

1.0

1.2

Rel

ativ

e re

spon

se (90

Sr-

Y :

30 c

m s

tand

ard)

JIS standard(EB1 type)500 keV to2.2 MeV

±30%500 keV to2.3 MeV(product

specification)

Beta ray residual maximum energy (MeV)

-70 %-60 %-50 %-40 %-30 %-20 %-10 %

0 %10 %20 %30 %

-70 %-60 %-50 %-40 %-30 %-20 %-10 %

0 %10 %20 %30 %

Below

AboveReference0°

Left Right

(a) Angular response (beta ray, above and below)

(b) Angular response (beta ray, left and right)

20° below

40° below

60° below

80° below

20° above

40° above

60° above

80° above

Reference0°

20° left

40° left

60° left

80° left

20° right

40° right

60° right

80° right


Fig.9 Neutron angular response

Fig.8 Neutron energy response

Table 2 Specifications of the gamma-neutron dosemeter

Fig.7 Gamma-neutron dosemeter

in Fig. 5.In order to conform to the revised JIS Z 4312

standard, beta ray angular responses were improvedas shown in Fig. 6. This improvement was achievedthrough widening the solid angle of beta ray incidenceand enlarging the beta ray entrance window. The betaray entrance window uses reinforcing material and isconstructed so as not to be damaged under normalhandling conditions.

3.2 Gamma-neutron dosemeterThe gamma-neutron dosemeter is equipped with

two sensors, one for detecting gamma (X) rays and theother for detecting neutrons, enabling both types ofradioactive rays to be counted simultaneously (Fig. 7).Main specifications of the gamma-neutron dosemeterare listed in Table 2.

Dosemeter model NRY50312

Detector Semiconductor

Radiation detected Gamma (X) rays Neutrons

Energy range 50 keV to 6 MeV 0.025 keV to 15 MeV

Energy response ±20 %,137Cs standard

-50 to +150 %, (thermal neutron

and 241Am-Be source:

252Cf standard

Angular response

±15 %,Up to 60°


137Cs standard

±50 %,Up to 60°

vertically and horizontally, 252Cf standard

Indication range 0 to 999.99 mSv 0 to 999.99 mSv

Accuracy of indication

±10 %,0.1 to 999.9 mSv

±20 %,0.3 to 999.9 mSv

Alarm Sound level: 100 dB or greater, Display lamp: flashing LED (red)

Communication method Wireless (LF) and point contact

Power suppliesNiCd rechargeable battery

(providing power for 12 or more hours of continuous operation)

Ambient temperature 0 to 50°C

Size 110×57×17 (mm)

Mass 120 g

The gamma (X) ray sensor is similar to thegamma-beta dosemeter and its description is omittedhere.

Because neutrons lack an ionization effect andcannot be detected directly, the neutron sensor reactshydrogen or boron atoms with neutrons, and thendetects the charged particles generated from thatreaction. Moreover, due to the wide energy range(from thermal neutrons to 15 MeV) to be measured bythe neutron sensor, two types of sensors are provided,a thermal neutron sensor for low energy use and a fastneutron sensor for high energy use. The silicon sensorchip of the thermal neutron sensor is formed with aboron thin film on its surface and is sealed within thesensor package.

10B atoms contained in the boron film have a largecross-sectional area within which to react with lowenergy neutrons, and alpha rays and Li nuclei generat-ed from this reaction are detected by the silicon sensor.

In the fast neutron sensor, polyethylene (CH2) is

-50 to +150%0.025 eV to 15 MeV

(product specification)

Rel

ativ

e re

spon

se (

252 C

f st

anda

rd)

Neutron energy (MeV)2.5 3.0 3.5 4.0 4.52.01.51.00.50

0.5

0

1.0

1.5

2.0

2.5

3.0

-100 %

-80 %

-60 %

-20 %

-40 %

0 %

20 %

-100 %

-80 %

-60 %

-20 %

-40 %

20 %

0 %

15° below30° below

60° below

60° below

75° below

90° below

15° above30° above

45° above

60° above

75° above

90° above

(a) Neutron angular response (252Cf, above and below)

Reference0°

15° left30° left

45° left

60° left

75° left

90° left

15° right30° right

45° right

60° right

75° right

90° right

(b) Neutron angular response (252Cf, left and right)

Below

Above

Left Right

Reference0°


Fig.10 Dosemeter calibration method

Table 3 Area access control apparatuses

Delivery to : Company A Company B Company C Company D

Ext

ern

al

appe

aran

ceF

eatu

res Integrated dosemeter storage

rack. Number of dosemeters

: 150 units

Dosemeters : NRY1, NRN1Transit method : flapper gateTransit time : approx. 15 sSize : approx. 1,440 (H)×1,350 (W)×300 (D) (mm)Mass : approx. 300 kg

Dosemeter : NRY4Transit method : flapper gateTransit time : approx. 7 to 8 sSize : approx. 1,300 (H)×1,100 (W)×300 (D) (mm)Mass : approx. 160 kg

Dosemeters : NRY5, NRN5Transit method : pole gateTransit time : approx. 7 to 8 sSize : approx. 1,700 (H)×1,120 (W)×420 (D) (mm)Mass : approx. 210 kg

Dosemeters : NRY6, NRN6Transit method : no gateTransit time : approx. 7 to 8 sSize : approx. 1,600 (H)×780 (W)×400 (D) (mm)Mass : approx. 200 kg

Compact, lightweight, space-saving design

Large LED used for alarm indicator

Wireless communication with ID card (breast pocket)

Spe

cifi

cati

ons

disposed on the silicon sensor within the sensorpackage, and the silicon sensor detects recoil protonswhich are generated in reactions between neutronsand the hydrogen atoms contained in the polyethylene.

The neutron sensor is calibrated using a 252Cfsource (having an average energy of 2.3 MeV). Inactual usage, it is important that a calibration con-stant, suitable for the radiation field of the workenvironment, be acquired in advance, and for thispurpose a correction constant that allows a variableweighting of the count values of the thermal neutron

sensor and fast neutron sensor is set internally, andthe weighting is calculated according to the actualwork environment in order to display the correct dosevalue.

Energy response is shown in Fig. 8 and angularresponses are shown in Fig. 9.

4. Area Access Control Apparatus

Installed at the border of the controlled area, thearea access control apparatus automatically screens

Calibration apparatus

Practicalcalibration

Standardcalibration

Calibration categoryExposure dose (rate) standard

Personal dosemeter Personal dosemeter

Designated standardinstrument

Designated secondary standard instrument

Exposure dose (rate)Japanese national standard

Primary exposuredose (rate) standard

Secondary exposuredose (rate) standard

Phantomcalibration

Dose equivalentconversion factor

Calibrationwithoutphantom

ICRU slab doseequivalent (rate) standard

ICRU slab doseequivalent (rate) standard

Practical exposure dose (rate) orpractical air kerma (rate) standard

Gamma ray irradiatorX-ray irradiator



Standard gamma ray source

Practical gamma rayirradiator

Practical standardgamma ray source

Standard measuring instrument

Practical standardmeasuring instrument


Fig.11 Gamma-beta calibration apparatus

access to the controlled area, and possesses thefollowing features.(1) The exchange of data (such as dose data, doseme-

ter number, time length accessing to the con-trolled area, alarm value, etc.) between the elec-tronic dosemeter and the apparatus is implement-ed via wireless communication.

(2) A reduction in transit time is achieved by simpli-fying input of the job number and by displaying aselectable list of the latest jobs on a screen whenentering the area.

(3) The entire apparatus has a low profile form andhigh functionality.

Main components of the apparatus include anoperation screen, a dosemeter communications unit, anID card reader, a human presence sensor and a statusindicator light. According to user needs, the apparatusmay be integrated with an electronic dosemeter stor-age rack, and may be equipped with a gate and so on.Features and specifications of apparatuses that havebeen delivered to nuclear power related facilities arepresented in Table 3. As can be seen from the

Fig.12 Neutron calibration apparatus

M

7.2°

Cylinder for gamma ray irradiation

Sound volume meter

Beta ray irradiation unit(Rotates at the completion of each measurement and calibrates 50 dosemeters.)

Simultaneous irradiation of 50 dosemeters

Case for storing gamma ray source

An arbitrary gamma ray source is selected from among 6 slots.

Secures the cassette. Detects presence of a cassette.

Dosemeter (4 units)

252 Cf source rises up to measurement position, and then dosemeter calibration begins.

Controlboard

Robotic arm

Dosemeter locker(stores 5 cassettes)

252 Cf source


photographs of the apparatuses, the absence or pres-ence of a gate, apparatus design, color and otherfeatures will distinguish each location where such anapparatus is installed. These products are made tocorrespond to a diverse array of user needs.

5. Calibration of Electronic Dosemeters

Electronic personal dosemeters must be calibratedin accordance with the method of JIS Z 4511, illustrat-ed in Fig. 10. In accordance with the JapaneseMeasurement Law, an accredited laboratory calibratesan electronic personal dosemeter to which a phantomis attached, and then by using this calibrated doseme-ter as a practical standard measurement instrument,other personal dosemeters of the same type can becalibrated by the substitution method without the useof a phantom. This method complies with the JISstandard for practical calibration and practical calibra-tion by this method is thought to be possible not onlywith gamma rays, but also with beta rays andneutrons. Because the practical calibration of electron-ic dosemeters requires the calibration of many elec-

tronic dosemeters, Fuji Electric is developing practicalcalibration equipment such as a panoramic irradiatorand a machine automated by means of a robotic arm.Figure 11 illustrates an example of a gamma ray andbeta ray calibrating apparatus, and Fig. 12 illustratesan example of a neutron calibrating apparatus.

6. Conclusion

Fuji Electric’s efforts in the field of personal dosemonitoring systems have been presented with a focuson electronic personal dosemeters. So that thesedevices can be used in a wider range of facilities in thefuture, Fuji Electric intends to develop electronicdosemeters that are easier to use and have lower costand greater accuracy in order to expand the scope ofapplications.

Finally, the authors wish to express their apprecia-tion and gratitude to all those individuals at electriccompanies, nuclear power facilities and various re-search organizations who provided considerable guid-ance and assistance in the development and commer-cialization of the electronic personal dosemeter.


Toshihiro TakagiOsamu KimuraAtsushi Minagoshi

Environmental Radiation Monitoring System

1. Introduction

In order to ascertain conditions near the perimeterof a supervised area at a nuclear power plant or otherfacility that uses radiation, environmental radiationmonitoring systems operate to continuously measurethe environmental gamma-ray dose rate.

Moreover, in recent years, in order to provide thegeneral public with a better understanding of theoperation of nuclear power plants, measurement datais being reported publicly and sent to nuclear environ-mental monitoring facilities administered by localmunicipalities, and this dissemination of information

has become an important service.This paper describes Fuji Electric’s latest environ-

mental radiation monitoring system.

2. System Configuration

The system is configured from a monitoring post ormeteorological equipment installed at the perimeter ofa supervised area at a nuclear power plant, a telemeterthat transmits measurement data to a main controlroom in the nuclear power plant, and a central datamonitoring device that displays and controls themeasurement data and alarms. Figure 1 shows an

Fig.1 System configuration (example)

Monitoring post (at perimeter of a supervised area) Equipment inside the power plant

NaI

dete

ctor

Teleme-ter, localstation

Teleme-ter, localstation

ICde

tect

or

Measuringunit

MO

Alarm indicator light

Optical converter

Communicationdevice

Communicationdevice

Optical converter

Precipitation detector

UPS

Air conditioner, fluorescent light, fan, etc.

External power source

Radioactive dust monitor

Metrological equipment

Distribution board,Lightning-resistant

transformer

Opt

ical

cab

leP

ubl

ic p

hon

e li

ne

Measuringunit

MO

Monitoring post (in surrounding municipalities)

NaI

dete

ctor

ICde

tect

or

Measuringunit

MO

Alarm indicator light

Transmitter

Communicationdevice

Digital display for promotional use

UPS

Air conditioner, fluorescent light, fan, etc.

External power supplies

Distribution board,Lightning-resistant

transformer

Measuringunit

MO

Telemeter,master

station A

Telemeter,master

station B

Main control room monitoring board

Transmissionmonitoringboard

Communicationdevice

Transmitter

Telemeter,master

station A

Telemeter,master

station B

Datatransmitter

Computer room

Equipment for transmitting to

local municipalities

Radiation controlsystem

Process computer

Datamonitoring

device

Emergency headquarters

Terminaldevice

Large-screenplasmadisplay

Display, monitor,control apparatus

Alarmdisplay

Dose ratedisplay

Dose raterecord


example configuration of the system.

3. Monitoring Post

A monitoring post has a structure that houses adose rate measuring device for continuous measure-ment of the environmental gamma-ray dose rate.Moreover, a structure equipped with both a dose ratemeasuring device and a radioactive dust monitor formeasuring the concentration of airborne radioactivedust is known as a monitoring station. Monitoringposts and monitoring stations are generally installedat 3 to 9 sites near the perimeter of a supervised areaof a nuclear power plant, and at 3 to 22 sites in thesurrounding communities.

3.1 Environmental gamma-ray dose rate measuring deviceIn accordance with the guidelines for environmen-

tal radiation monitoring, the environmental gamma-ray dose rate is measured over a wide range, from thebackground (BG) level (several tens of nGy/h) to108 nGy/h. Measurement is therefore implementedwith the combination of a NaI (Tl) scintillation detector(see Fig. 2) for measuring low dose rates and aspherical ionization chamber detector (see Fig. 3) for

Fig.2 NaI (Tl) scintillation detector

measuring high dose rates.Digitalization and small, high-density packaging

technology enable the dose rate measuring device to berealized with a simple basic configuration that com-bines a detector unit and a measurement unit (havingdimensions of approximately 21 (W) × 23 (H) × 30 (D)(cm)) (see Fig. 4) to achieve space savings and highreliability.

The detector unit of the low dose rate measure-ment system is equipped with an NaI (Tl) scintillator,a photomultiplier, an amplifier circuit, a high voltagecircuit and a temperature compensating circuit, and iscapable of outputting standardized pulse signals fromthe detector, without any temperature dependence.The measurement unit has two CPU boards, one boardis for measurement use and contains an approximately6-inch thin film transistor (TFT) color display and anenergy compensation circuit, and the other board is fordisplaying, transmitting and storing the measureddata. Because this measurement system uses anenergy compensation method of spectral weightingwith a digital weighting method (DWM), the conver-sion into a dose rate can be accomplished withoutdecreasing the count precision, and a spectral dataanalysis function is able to identify radioisotopes fromthe gamma-ray energy information. Spectral data isalso transmitted to the main control room at fixedintervals so that analysis can be performed offsite.

The detector unit of the high dose rate measure-ment system is equipped with an ionizing chamber, anamplifier circuit, a voltage frequency translation cir-cuit and a high-voltage circuit. The measuring unitcounts pulse signals sent from the detector unit anddisplays dose rate data. For this measurement system,some spherical ionization chamber detectors were alsomade from aluminum material, which has a smallerspecific gravity than the conventional stainless steelmaterial, enabling improved measurement accuracy ofgamma-rays in the low energy range of less than

Fig.3 Spherical ionization chamber detector

Fig.4 Measurement part of dose rate measuring device


400 keV.The method of onsite recording of measurement

data has changed from the conventional method ofdata recording with a data logger to a method in whichmeasurement values are digitized and then stored onan optical disk. This method makes it possible toascertain measurement value fluctuations, record thedevice status, and expand the data storage period,while also enabling data analysis to be performedsimply with the use of a personal computer.

The high dose rate measurement system normallyuses a spherical ionization chamber detector, but inorder to provide the low dose rate measurementsystem with the capability to compensate measure-ments when trouble arises, a wide range NaI (Tl)scintillation detector capable of measuring the rangefrom BG level to 108 nGy/h was developed and thesystem configured. In the low range from BG level to105 nGy/h, this system measures and processes pulsesignals from the detector. In the high range above105 nGy/h at which pulses cannot be measured, thesystem measures and processes an electric currentsignal that is proportional to the dose rate.

Main specifications of the low range measurementsystem, the high range measurement system and thewide range NaI measurement system are listed in

Table 1.

3.2 Radioactive dust monitorThe radioactive dust monitor is a device that

continuously measures the concentration of radioactivedust in the air. The detector unit measures beta-raysusing a plastic scintillation detector, and integratesdust sampler and dust monitor that measures theconcentration of dust collected in a paper filter. Alsoprovided is a function that automatically samplesradioactive iodine in a charcoal cartridge in caseswhere the environmental gamma-ray dose rate exceedsa preset alarm value.

The sampling pump uses an inverter to provideconstant flow control and enable continuous samplingat the constant flow rate of 250 L/min even in caseswhen the flow rate fluctuates due to clogging of thepaper filter or the like.

3.3 Monitoring stationThe monitoring station (see Fig. 5) is assembled

from precast autoclaved lightweight concrete (ALC)boards, the use of which shortens the time necessaryfor construction and reduces cost.

In order to publicly report the environmentalradiation measurement data, monitoring stations in-

Fig.5 Appearance of monitoring station

Table 1 Main specifications

Item Low-range measurement system High-range measurement system Wide-range NaI measurement system

Detector

Detector size

Measurement range

Reading error

Energy dependency

Directional dependency

Temperature characteristics (20°C standard)

NaI (Tl) scintillation detector Spherical ionizationchamber detector

NaI (Tl) scintillation detector (with energy filter)

2-inch diameter×2-inch height, etc. Approx. 14.5 L 2-inch diameter×2-inch height

BG level up to 105 nGy/h BG level up to 108 nGy/h BG level up to 108 nGy/h

Within ±10 % Within ±10 % Within ±20 %

50 keV to 3 MeV : within ±10 % 50 to 400 keV : within ±15%0.4 to 3 MeV : within ±10%

50 to 100 keV : within ±20 %50 keV to 3 MeV : within ±10 %



Fig.6 Digital display


stalled in the communities surrounding a power plantare provided with a graphic panel that explains therole of the monitoring post and shows the locations ofnearby monitoring posts, and a high-intensity lightemitting diode (LED) display (see Fig. 6) that digitallydisplays the environmental gamma-ray dose rate.

Because the monitoring panel installed inside amonitoring station is a front maintenance-type panel,it can be installed with its rear surface in closeproximity to a wall. By eliminating the rear mainte-nance space that had been necessary in the past,space-savings is achieved inside the monitoring sta-tion.

As measures against radiation fluctuation due toradon and thoron, an air blower is provided toventilate the air in the detector unit and a heatexchanger ventilation apparatus is provided to venti-late the air inside the monitoring station so that thereis no change in temperature.

Additionally, a mechanism for transporting detec-tors mounted on the roof into the monitoring station isprovided. Because the spherical ionization chamberdetector is particularly heavy, the use of a hoistingmachine improves operability and safety.

4. Telemeter

The 24-hour-per-day continuous transmission ofdata from a monitoring post to the monitoring board inthe main control room is implemented via a transmis-sion system in which a programmable controller (MICREX series), having a proven track record of highreliability, is configured as a telemeter. At monitoringposts near the perimeter of a supervised area at apower plant, optical fiber cable is used in the transmis-sion path in order to prevent erroneous signals causedby the commingling of exogenous noise due to lighten-ing or the like. At monitoring posts in the surroundingcommunities, public phone lines are used so that atransmission path can be secured easily.

The telemeter uses a broadcast transmission proto-col that eliminates the need for the application soft-ware to acknowledge the transmission or reception ofdata. Measurement data from the monitoring post canbe refreshed in 1-second cycles, and high-speed andhighly reliable transmission is realized.

In consideration of the possible occurrence of atransmission path malfunction, the monitoring posttelemeter is provided with the capability to store up toa maximum of 14 days of measurement data (valuessampled every 30 seconds) in a memory card. Afterproper operation is restored, storage data can also becollected from the central data monitoring device orthe like.

The main control room’s telemeter (master station)that collects measurement data from each monitoringpost is implemented as a dual-redundant system inorder to avoid data dropout due to device malfunction.

This redundancy increases the system reliability.Additionally, because the telemeter is provided

with a computation function for converting a monitor-ing post’s measurement data into the dose rate, and isable to perform what was previously a function of thecomputer system — the calculation of alarm settingvalues and conversion of measurement data intoscientific values — the system can be simplified.

Furthermore, because the telemeter can expandcontrol through PE link transmission (Fuji Electric’sproprietary LAN), and is equipped with communica-tion interfaces for serial communication, Ethernet*1

and the like, the transmission of measurement dataeven to nuclear power environmental monitoring facili-ties administered by local municipalities can be imple-mented easily.

5. Data Monitoring Device

The data monitoring device that displays data,monitors the system operation status, creates forms,etc. is centrally located, where measurement data fromthe monitoring posts is collected, stored and thenaggregated. The data monitoring device is selectableas a Unix*2 server, FA computer, or the like accordingto the system size, and is designed for 24-hourcontinuous monitoring.

An example of the main functions is presentedbelow for the case when a Unix server is used as thedata monitoring device.

5.1 Screen display(1) List of present dosage rates

Displays a list of the present values of the doserate data and meteorological data(2) Dose rate map display (see Fig. 7)

Displays present values of the dose rate data andmeteorological data on a topographic map at the

Fig.7 Dose rate map display

*1 Ethernet: A registered trademark of Xerox Corp., USA

*2 UNIX: A registered trademark in USA and othercountries licensed by X/Open Co. Ltd.


location of the monitoring post(3) Dose rate trend display

Displays the dose rate data and precipitation datain a trend graph

By displaying the dose rate and precipitation dataat the same time, the change in dose rate thataccompanies precipitation can be assessed quickly.Also, the scale of the graph’s vertical axis can bemodified automatically.(4) Alarm history display

Displays the incidence of and recovery from alarmsgenerated by the system(5) Alarm display panel

Displays the operating status of the system compo-nents in green (normal) or red (alarm generated) abovethe system configuration schema so that the operatingstatus can be assessed quickly(6) Spectral data display

Displays the spectral data per station or as a timeseries in 10-minute intervals(7) Setup of operating constants

Sets the alarm values and the conversion constantfor converting measurement data to scientific values

This setting screen manages security according tothe security classifications of password administrator,setting modifier and setting visitor.

5.2 Form output(1) Daily report

Prints the dose rate and other values (hourlyvalues) of each monitoring post for a specified day(2) Monthly report

Prints the dose rate (hourly values) and controlstandard values (average hourly values of the priorfiscal year ±3 σ) of each monitoring post for a specifiedmonth(3) Dose rate trend

Prints trends such as the dose rate for a specified

period

5.3 Emergency headquarters data display functionThe emergency headquarters of a nuclear power

plant is provided with a large-screen plasma displayand an emergency system capable of displaying vari-ous types of plant information so that the plant statuscan be assessed accurately in the case of an emergency.Environmental radiation data is also critically impor-tant data in an emergency.

This system is provided with a function for easilyoutputting environmental radiation data by connectingthe data monitoring device to a LAN, so that it can belinked to this emergency system.

6. Conclusion

Extremely high reliability is required of an envi-ronmental radiation monitoring system because itmust perform continuous 24-hour-per-day monitoringof the area surrounding a nuclear power plant (exceptduring scheduled system maintenance), without anydata dropout. Recently, measurement data fromenvironmental radiation monitoring systems is beingtransmitted to nuclear environmental monitoring facil-ities administered by local municipalities and is alsobeing displayed on each power plant’s website.

Within this context, Fuji Electric intends to employsuch comprehensive technologies as radiation mea-surement, data transmission, and computer systembased control to their fullest extent and to developsystems with even higher reliability to meet customerneeds.

The authors are extremely grateful for all theassistance received from employees of The KansaiElectric Power Co., Inc., the Ooi Power Station andother electric power companies and research institutes.


Hironobu KobayashiTsuyoshi SakamakiKaoru Masui

Environmental RadiationMeasuring Equipment

1. Introduction

Environmental radiation measuring equipment iscommonly used at such facilities as nuclear powerplants, research laboratories and hospitals for thepurpose of measuring and controlling environmentalradiation. Fuji Electric supplies various types ofenvironmental radiation measuring equipment thatsupport a variety of applications. In response to recentdemands for environmental radiation measuringequipment that is smaller in size, has higher sensitivi-ty and requires less labor, new products are beingurgently developed to meet these needs.

This paper presents an overview of environmentalradiation measuring equipment and introduces newmodels developed recently.

2. Environmental Radiation Measuring Equip-ment: Types and Uses

Fuji Electric’s radiation measuring equipment canroughly be categorized as radiation control equipment,radiation monitoring equipment, and the detectors

incorporated therein. Table 1 lists Fuji Electric’s mainproducts and their uses.

The survey meter is a representative example ofradiation control equipment and is conveniently usedto locate radiation leaks and search for surface con-tamination and radiation sources within a facility.Two types of recently developed radiation measuringequipment are introduced here, a low dose environ-mental dosemeter and a portable monitor post. Both ofthe radiation measuring devices have a simple configu-ration that can be connected to a PC for dataprocessing, and they are portable for environmentaldosimetry anywhere regardless of location. The lowdose environmental dosemeter uses a semiconductordetector having approximately 100 times higher sensi-tivity than prior models (compared to prior modelsfrom Fuji Electric) and is capable of measuring lowlevel doses. The portable monitor post uses a wide NaI(Tl) scintillation detector which is a single detectorranging from natural low dose rates to high dose rates.

Table 1 Main types of radiation measuring equipment

Type Product name Use Measured radiation Measurement range

Radiation control equipment

Ionization chamber type survey meterScintillation type survey meterGM type survey meter

Neutron REM counterPersonal dosemeter

1 cm dose equivalent, X instantaneous dose measurementLow level radiation monitoring and searchingMeasurement of leaking gamma doses and beta surface contaminationMeasurement of leaking neutron dosesControl of personal exposure at nuclear power facilities and the like

γ (X) rays, β rays

α rays, β rays, γ raysβ rays, γ rays

NeutronsNeutrons, β rays, γ rays

1 µSv/h to 30 mSv/h

1 to 104 counts/s1 to 105 counts/m

0.1 µSv/h to 9.999 mSv/h0.01 to 1,000 mSv

Radiation monitoring equipment

Portable monitoring postLow dose environmental dosemeter

Outdoor environmental dosimetryEnvironmental dosimetry

γ rays γ rays

10 to 108 nGy/h0.01 to 999,999.99 µSv/h

Detectors, etc.

Semiconductor area monitordetectorDust monitor semiconductor α-ray and β-ray detectorScintillation detector

γ-ray ionization chamber detectorRI calibrator

Monitoring and measurement of air gamma doses at radiation facilitiesCounting of alpha and beta rays contained in airborne dustDetector housed in a process monitor and the likeMonitoring and measurement of air gammadoses at radiation facilitiesRadioactivity measurement of medical radio isotopes used at hospitals

γ rays

α rays, β rays

γ rays

γ rays

γ rays

0.1 µSv/h to 10 mSv/h

1 to 105 counts/m

Varies according to use

Varies according to use

0.1 MBq to 99.99 GBq


3. Low Dose Environmental Dosemeter NSDSeries

3.1 OverviewFuji Electric Systems and the Tsuruga Power

Station of The Japan Atomic Power Company began tocollaboratively develop a series of low dose environ-mental dosemeters in 2000, and realized a successfulcommercial product in March 2004. This newlydeveloped low dose environmental dosemeter NSD3has approximately 100 times higher sensitivity thanthe ones in the past, which enables low level measure-ment as low as 0.01 µSv, compared to the previousmodels that could not measure doses below 1 µSv. Aninternal battery is installed in the dosemeter storagepost for three-month continuous monitoring that canprovide a longer trend than conventional one-weektrend. This allows data collection for a three-monthdose trend as same as thermoluminescence dosemeters(TLD), a longtime environmental monitoring means inthe vicinity of nuclear power plants. In terms of easydata collection mechanism, our environmental doseme-ters excel the conventional thermoluminescences,which saved labor costs, and then were implementedas a replacement with TLD. The system process flowis shown in Fig. 1.

3.2 Features and specifications(1) Low dose environmental dosemeter

Features are listed below.(i) The structure of the main unit is water/splash-

proof that resists condensation and splash.(ii) The high sensitivity of the detector enables

background (BG) level variation to be moni-tored.

(iii) Three channels of energy information data canbe stored.

(iv) Non-contact communication (infrared commu-nication) is provided to communicate with itsdata collection terminal.

(v) Measurement data are stored in non-volatilememory so that the data can be read in anevent of NSD3 malfunction.

Main specifications are listed in Table 2.(2) Data collection terminal

The data collection terminal can store measure-ment results of the low dose environmental dosemeterand the features are listed below:

(i) Small size and light-weigh. Carried with theshoulder strap.

(ii) The terminal can collect and store three-monthcumulative data from a maximum of 20 lowdose environmental dosemeters NSD3.

(iii) Can maintain the data after battery expira-tion.

(3) Data processing systemData stored in the data collection terminal are

transferred through an RS-232C cable to a dataprocessing unit (PC). The stored data can be displayedas a list of a 1-hour cumulative dose or as count valuesper energy level. If a large fluctuation in a trend datais observed, 1-minute trending feature is available forthat data sampled to analyze in detail.(4) Post for low dose environmental dosemeters

A battery is installed inside the dedicated doseme-ter storage post for continuous low dose environmentaldosimetry for three months or longer. The post hasgood ventilation to prevent an increase in internaltemperature when exposed to direct sunlight, andwater-resistant design that prevents rainwater infil-tration. Even if installed in the post, the low doseenvironmental dosemeter NSD3 is able to communi-cate with the data collection terminal.

3.3 Characteristic data of the low dose environmentaldosemeterThe dose rate linearity, at relative sensitivity (137Cs

reference), is within ±10 %. Also, angular responses(vertical and horizontal) for the low dose environmen-tal dosemeter NSD3 when installed in the post arewithin ±30 % (137Cs reference), (not including the deadzone due to the battery). Angular responses are shownin Fig. 2.

Table 2 Specifications of the low environmental dosemeterNSD3

Fig.1 Process flow for a low dose environmental dosemetersystem

LAN

Data processing

At the post...

In the control room...

Data collection

Item

Radiation detected γ (X) rays

50 keV to 6 MeV

0.01 to 999,999.99 µSv

±10 % (137Cs)

±30 % (excluding dead zones)

-10 to +50°C

80 (W)×140 (D)×29 (H) mm

Approx. 300 g

Energy range

Measurement dose

Accuracy of reading

Angular response

Ambient temperature

Size

Mass

Description


3.4 Field comparison dataComparison data for the low dose environmental

dosemeter and a monitoring post (NaI detector) isshown in Fig. 3. Low dose environmental dosemeterreadings (count values) follow fluctuations in monitor-ing post readings (nGy/h). This indicates that doseme-ter is able to measure the background level doses withhigh precision.

4. Portable Monitor Post

4.1 OverviewThe portable monitor post uses a wide NaI (Tl)

scintillation detector and is able to measure air gammadose rates over a wide range from the BG level to108 nGy/h. Featuring compact size and light weight,this portable monitor post can easily be transportedand used for measurement. An internal global posi-tioning system (GPS) and data transmission terminalenable transmission of dose rate and position informa-tion via a cell phone or other systems. For this reason,the portable monitor post is used as an environmental

Fig.3 Comparison with monitoring post

Fig.5 Example of environmental radiation dose rate map

Fig.4 Appearance of the portable monitor post

Fig.2 Angular response of low dose environmental dosemeter when installed in the post

radiation monitoring post for emergency responses. Itsexternal appearance is shown in Fig. 4.

An example of an environmental radiation doserate map that uses the dose rate and location informa-

330° 30°

300° 60°

270° 90°

240°

210°

120°

150°

180°

0°

80 %

60 %

40 %

20 %

0 %

100 % 330° 30°

300° 60°

270° 90°

240°

210°

120°

150°

180°

0°

80 %

60 %

40 %

20 %

0 %

100 % 330° 30°

300° 60°

270° 90°

240°

210°

120°

150°

180°

0°

80 %

60 %

40 %

20 %

0 %

100 %

Condition: 137Cs 10 µSv

(a) Horizontal (b) Top (c) Vertical

(Cou

nt)

(nG

y/h

)

Date and time

1,400

1,600

1,800

1,200

1,000

800

600

400

200

10/2

9 16

: 27

10/3

0 4

: 27

10/3

0 16

: 27

10/3

1 4

: 27

10/3

1 16

: 27

11/1

4

: 27

11/1

16

: 27

11/2

4

: 27

11/2

16

: 27

11/3

4

: 27

11/3

16

: 27

11/4

4

: 27

11/4

16

: 27

11/5

4

: 27

11/5

16

: 42

11/6

4

: 42

11/6

16

: 42

11/7

4

: 42

11/7

16

: 42

11/8

4

: 42

11/8

16

: 42

11/9

4

: 42

11/9

17

: 29

11/1

0 5

: 29

11/1

0 17

: 29

11/1

1 5

: 29

11/1

1 17

: 29

11/1

2 5

: 29

11/1

2 17

: 29

11/1

3 5

: 29

100

120

140

160

180

200

80

600

Left axis: Environmental dosemeter (count)

Right axis: Station (nGy/h)


tion is shown in Fig. 5.

4.2 FeaturesThe features are listed below:

(1) The portable monitor post may be used as abackup for non-moveable environmental radiationmonitors.

(2) Compact size and lightweight structure of theportable monitor post makes it easy to transportand install.

(3) All-weather type for outdoor installation. Can bepowered by an external battery when installed inwhere AC power is unavailable.

(4) Internal memory can store a 1-week measurementvalues (values measured every 1 minute).

(5) An energy response compensation circuit and atemperature compensation circuit are provided.

4.3 SpecificationsThe specifications are listed in Table 3.

4.4 CharacteristicsSo that a single detector can cover measurements

in the range of 10 to 108 nGy/h, the detector is useddifferently for the low and high range regions. For thelow range region, it is used as a pulse-output typedetector and for the high range region, it is used as acurrent-output type detector. Energy responses foreach region are shown in Figs. 6 and 7.

5. Conclusion

The objectives of radiation control are to reduceexposures much further, to save labor and enhancefunctionality for dosimetry. Because the low doseenvironmental dosemeter and the portable monitorpost achieve nearly the same performance as conven-tional large-sized measuring equipment and can storegreater quantities of radiation data, future applica-tions are expected. In the future, Fuji Electric intendsto improve the performance in low energy and angularresponse.

In conclusion, the authors wish to express theirgratitude to all members of the Environmental SafetyDepartment of The Japan Atomic Power Company’sTsuruga Power Station from whom we received guid-ance and data useful in the development of the lowdose environmental dosemeter.

Table 3 Specifications of the portable monitor post

Item Specification

Dose rate measurement range

10 to 108 nGy/h Low range region : 10 to 5×105 nGy/h High range region : 3×105 to 108 nGy/h

Dose rate measurement accuracy

±10 % (reference : for 137Cs exposure)

Angular response ±20 % (0 to ±90°)

Energy response

Low range area : ±20 % (from 50 keV to less than 100 keV) ±10 % (from 100 keV to 3 MeV)High range area : -50 to +25 % (from 50 keV to less than 100 keV) -10 to +20 % (from 100 keV to less than 400 keV) ±10% (from 400 keV to 3 MeV)

Variation ofindications Coefficient of variation: 0.1 or less

Temperature characteristics ±5 % (20°C reference)

Fig.7 Energy response in high range region

Fig.6 Energy response in low range region

Res

pon

se r

atio

Energy (keV)10010 1,000 10,000

0.7

0.4

0.1

1

1.3

JIS allowable range

Res

pon

se r

atio

Energy (keV)10010 1,000 10,000

0.7

1

1.3

1.6

1.9

0.4

0.1

JIS allowable range


Toru HasegawaTadao HashimotoManabu Hashimoto

Radioactive Contamination Monitors

1. Introduction

In order to prevent the spread of radioactivecontamination to areas outside a controlled area at anuclear power plant, surface contamination inspectionmonitors are installed at the perimeter of the controlarea, and all articles moved from inside the controlarea to outside are monitored for surface contamina-tion. The main types of surface contamination moni-tors include body surface contamination monitors thatmeasure the surface contamination on a worker’s body,article surface contamination monitors that measurethe surface contamination of articles ranging in sizefrom large objects such as a scaffolding boards to smallobjects such as portable tools carried by workers, andlaundry monitors that measure the surface contamina-tion of clothes worn by workers inside the controlledarea.

Other types of radioactive contamination monitorsinclude a whole body counter that measures theinternal exposure (internal contamination) levels ofworkers who work inside controlled areas, and a hand-foot-clothes monitor which is used mainly in hospitalsand measures the surface contamination on hands, feetand clothes.

Fuji Electric uses large-area radiation detectors,signal processing units capable of high-speed arith-metic processing, mechanical units that establish theoptimal conditions for measurement, and human-machine interfaces that use audible guidance and/or alarge-screen color liquid crystal displays (LCDs) tomake the high-sensitivity high-speed measurement ofradioactive matter commercially practical, and hassupplied these monitors to nuclear power plantsthroughout Japan. Additionally, these monitors areprovided with a self-diagnosis function, which whenconnected to a data processing device apparatus,enables the central control of contamination inspectionand measurement data.

This paper presents brief overviews and descrip-tions of the features of these monitors.

2. Body Surface Contamination Monitor

2.1 OverviewThe body surface contamination monitor is in-

stalled at the exit of a controlled area and tests for thepresence of contamination on the body surface ofpeople exiting that controlled area. This apparatus isprovided with detectors positioned to sense the entiresurface of a person’s body, and it capable of highlyefficient contamination measurement within a shorttime. The height of the overhead detector adjustsautomatically so that the head region can be measuredwith good sensitivity. This adjustable height functionenables inspections for people of all heights, from shortelementary school age children to tall adults, or morespecifically from heights of 1,300 to 2,000 mm.

If the inspection finds no contamination, theworker is urged to go to the exit (non-controlled area),however if contamination is detected, the worker isprevented from exiting the controlled area. Figure 1shows the appearance of this apparatus.

2.2 Characteristics(1) Detection sensitivity

Beta-rays can be measured at a sensitivity of0.4 Bq/cm2. Conditions are listed in Table 1.(2) Detector unit

A large-area plastic scintillation beta-ray detectoris used.(3) Optimum measurement time operating function

Measurement is usually performed within a fixedperiod of time (settable according to the type ofoperation), however, in order to minimize processingtime according to the type of monitor, this functioncomputes the optimal measurement time that satisfiesthe detection sensitivity, based upon the background(BG) count rate, and sets these parameters automati-cally to enable measurement within the shortestamount of time possible.(4) Visitor function

The number of visitors has been increasing recent-ly and this function allows the operation to beexplained during measurement while the door is open.(5) Miniaturization of the apparatus


Fig.5 Transportable small article monitor (type 2)

Two models are available, one with dimensions of860 (W) × 1,200 (D) mm, and another model, developedfor the purpose of increasing the number of machineswithin a limited space, and having dimensions of 800(W) × 1,200 (D) mm. The inner dimensional width ofthe measurement room ranges from 400 to 500 mm forthe former, and 400 to 440 mm for the latter.(6) Easier maintainability

Maintenance can be performed in an open space ina non-controlled area.(7) Guidance function

Operational guidance for measuring is provided toworkers via an LCD and audible instructions. A modelhaving a function to switch the screen display andspoken instructions to the English language is avail-able to support use by non-Japanese speaking users.(8) Connection to the data processing apparatus

The interface to the data processing apparatus isselectable as a LAN or as serial transmission. Thedata processing apparatus enables real-time monitor-ing of the operation status, display of measurementresults, creation of forms and trend graphs, and the

Fig.4 Transportable small article monitor (type 1)

Fig.3 Small article transfer monitor

Fig.2 Large article transfer monitor

Table 1 Specifications of the body surface contaminationmonitor

Fig.1 Body surface contamination monitor

Item Specification

Detector Plastic scintillation detector

Number of detectors 15 to 18 detectors

Processing capacity Approx. 20 s

External dimensions 860 (W)×1,000 (D)×2,250 (H) (mm)

Inner dimensions of measurement room 500 (W)×700 (D)×2,000 (H) (mm)

Mass 780 kg

Detector sensitivity 0.4 Bq/cm2

0.1 µSv/h10 sU3O8 100×100 (mm)Hands & feet : close contactHead : 50 mmOther : 100 mm

Conditions :BGMeasurement timeRadiation sourceDistance

PrinterAC supply

unit


long-term storage of measurement data.(9) Improved design

Because the structure was designed to feel spa-cious and open, the subject being measured will notendure a sense of oppression.

3. Article Surface Contamination Monitor

3.1 OverviewThe article surface contamination monitor tests

whether there is any contamination on the outer orinner surface of an article carried out from thecontrolled area. Variations of this monitor include alarge object transfer monitor, a small article transfermonitor, and a personal handyphone system (PHS)transfer monitor. The appearance of each of thesemodels is shown in Figs. 2 to 6.

3.2 Common features(1) Detector sensitivity

Beta-rays can be measured at a sensitivity of0.4 Bq/cm2 and gamma-rays can be measured at asensitivity of 1.1 Bq/cm2. Conditions are listed inTable 2.

Table 2 Monitor specifications

(2) Use of a beta + gamma-ray detectorThe monitor is fitted with a detector that inte-

grates both a beta-ray and gamma-ray scintillator, andis able to measure the inner surface contamination(gamma-ray) of a pipe or the like.(3) Moveable overhead detector

The overhead detector is lowered according to theprofile of the article, and then measurement is per-formed. This enables the article to be measured at aclose range and achieves highly efficient measurementregardless of the profile of the article.(4) Safety measures

The moving parts of the apparatus, the conveyorand door, are provided with a bar switch or photoelec-tric sensor that halts their operation when touched inorder to prevent accidental entangling of the operator’sfingers or arms.

3.3 Large article transfer monitorThe large article transfer monitor is installed at

the exit for carrying out large objects, and is used tomeasure efficiently the contamination of large and flatobjects such as scaffolding boards and pipes that areremoved in large quantities from the controlled area

Monitorname

ItemLarge article

transfer monitorSmall article

transfer monitor

Transportable small article monitor

(type 1)

Transportable smallarticle monitor

(type 2)PHS transfer monitor

Detector Plastic scintillationdetector

Plastic scintillationdetector




Detectorpositioning

Top & bottom ofobject to be measured

0.4 Bq/cm2

0.1 µSv/h20 mm/s

U3O8 100×100 (mm)30 mm

0.4 Bq/cm2

0.1 µSv/h10 s

U3O8 100×100 (mm)30 mm

0.4 Bq/cm2

0.1 µSv/h10 s

U3O8 100×100 (mm)30 mm

0.4 Bq/cm2

0.1 µSv/h10 s

U3O8 100×100 (mm)30 mm

0.4 Bq/cm2

0.1 µSv/h10 s

U3O8 100×100 (mm)30 mm

Top & bottom, left &right,front & back ofobject to be measured




Detector sensitivity (beta-ray)Conditions : BG Moving speed or measurement time Radiation source Distance

1.1 Bq/cm2

0.1 µSv/h20 mm/s

60Co 100×100 (mm)30 mm

1.1 Bq/cm2

0.1 µSv/h10 s

60Co 100×100 (mm)30 mm

Detector sensitivity (gamma-ray)Conditions : BG Moving speed or measurement time Radiation source Distance

W1,500 mmD 4,000 mmH 300 mm

W 500 mmD 500 mmH 300 mm

W 420 mmD 300 mmH 270 mm

W 310 mmD 220 mmH 120 mm

W 160 mmD 60 mmH 30 mm

Size of object to be measured

W4,550 mmD 2,110 mmH 1,950 mm

W1,000 mmD 1,900 mmH 1,600 mm

W 560 mmD 550 mmH 750 mm

W 400 mmD 315 mmH 470 mm

W 260 mmD 350 mmH 270 mm

Size

200 kg 20 kg 5 kg 5 kg Lightweight objectsuch as a PHS phone

Mass of object to be measured

4,000 kg 1,800 kg 60 kg 18 kg 15 kgMass

™Steel scaffolding™Scaffolding material™Scaffolding board™Pipe

™Helmets™Tools™Writing instruments™Documents

™Documents™Tools™Writing instruments™Small measuring

instruments

™Documents™Tools™Writing instruments

™PHSExamples of objects to be measured


and right positions, entirely surrounding the article tomeasured. The other model is provided with detectorspositioned at the top and bottom (2 surfaces) of thearticle to be measured.(2) Storage of measured articles

After being measured, the articles are transferredto a conveyor on the non-controlled area side, where astocker that stores the measured articles may beattached. The number of articles storable by thestocker is selectable according to the operation as 8tiers of 100-mm-tall articles, 4 tiers of 300-mm-tallarticles, and so on.

3.5 Transportable small article monitor (type 1)The transportable small article monitor developed

for and delivered to customers in China is limited tothe measurement of helmets, documents and tools, andweighs only approximately 60 kg since it is providedwithout a drive mechanism. With its small footprint,this monitor is also suitable for temporary use whenlarge quantities of articles are being transported out ofthe controlled area.

The upper detector can be manually positioned atany of the 4 stages of 40, 120, 200 and 280 mm abovethe article loading surface.

3.6 Transportable small article monitor (type 2)This monitor weighs only approximately 18 kg,

which is even lighter in weight than the abovemen-tioned transportable small article monitor, and can bemoved easily by one worker wearing the shoulder beltaccessory. Also, an optional battery unit can be usedto power the monitor at locations where power couldnot otherwise be supplied.

3.7 PHS transfer monitorThis monitor is specialized for the measurement of

small articles such as PHS phones. With compactexternal dimensions of 260 × 350 × 270 (mm), thismonitor can be installed in the vacant space above acounter.

4. Laundry Monitor

4.1 OverviewThe laundry monitor is used to detect efficiently

the surface contamination of clothing worn inside thecontrolled area, before or after washing. The objects tobe measured are clothing such as overalls and under-garments, small articles such as hats, gloves andsocks, and molded articles such as helmets and shoes.

A front monitor inspects unwashed clothes and thelike, and screens out highly contaminated articles notsuitable for washing. The small article front monitoris an example of this type of monitor. A rear monitorinspects washed clothes and the like for residualcontamination, and the clothes monitor is one exampleof this type of monitor. A folding machine and a

during regularly scheduled inspections.(1) Processing capacity

The detector unit has a width of 1,500 mm, en-abling scaffolding boards, pipes and the like to bemeasured in bulk. For example, it is possible tomeasure more than 150 pipes (having a length of 4 m)within one hour.(2) Measurement method

Long articles such as scaffolding boards and pipescan be placed directly on the conveyor and measured.However, small articles such as clamps and bolts areplaced in a measuring dish and then measured.(3) Creation of transfer forms

By registering the article and its quantity prior tomeasurement, the monitor’s internal printer is able toprintout a transfer form.(4) Conveyor speed

Conveyor speed can automatically be set in therange of 10 to 100 mm/s, in increments of 10 mm/s.The automatic setting function calculates the optimalconveyor speed according to the BG level at theinstallation site and then sets the speed automatically.(5) Moving the apparatus

The apparatus is fitted with a moveable dolly (withtires), and in the case of a battery-powered self-propelled dolly, the apparatus can be moved with justone person.(6) Lateral movement

For locations having insufficient space for turningthe apparatus, sideways-oriented wheels are providedin order to allow lateral movement so that theapparatus may be moved to any arbitrary position.

3.4 Small article transfer monitorThe small article transfer monitor is installed near

the access control room, and is used to measureefficiently the contamination of small articles such aswriting instruments and tools that were hand-carriedby workers into the controlled area.(1) Detector positioning

Two monitor models are manufactured to corre-spond to the shape of the article to be measured forcontamination. One model is provided with detectorslocated at the top and bottom, front and back, and left

Fig.6 PHS transfer monitor


Fig.7 Clothing monitor, folding machinesorting machine automatically separate contaminatedarticles from normal articles. While separating thearticles, the folding machine automatically folds thenormal uncontaminated clothing. By connecting thesemachines to contamination monitors, labor savingsand higher throughput can be realized. This paper willintroduce the front monitor, small article front monitorand clothes monitor.

4.2 Features(1) Monitors for clothing, small articles and molded

articles, and the front monitor, are completelycompatible with the inspection goal and with thearticle to be measured.

(2) The clothes monitor and small article front moni-tor have detection sensitivities capable of detect-ing 1/10 the legally prescribed reference value forarticles removed from controlled areas.

(3) The high-capacity clothes monitor is capable ofprocessing about 250 pairs of overalls within onehour.

(4) The conveyor unit of the clothes monitor recentlyhas been using a resinous round belt having lowcost, low noise and long life, instead of theconventional wire net conveyor.

(5) A static eliminator is provided to protect workersfrom static electric shocks.

(6) The measurement system has an extensive self-diagnosis function that enables easy confirmationof the well-being of the system.

4.3 Function(1) Clothes monitor

This monitor measures clothes and small articlesafter they have been washed. When used in combina-tion with the folding machine, this monitor handlesclothes exclusively. The article to be measured isplaced into the monitor, picked up by a verticalconveyor and moved between upper and lower detec-tors, to inspect it for contamination. The large-areabeta-ray detector that is provided has no dead zonesover the entire width of the conveyor, and this monitorachieves smaller size and lighter weight than previousmodels. If a folding machine is connected, normalarticles and contaminated articles are separated auto-matically and the normal articles are folded. Theexternal appearance of the clothes monitor is shown inFig. 7 and its specifications listed in Table 3.(2) Small article front monitor

This monitor measures small articles exclusively,before they have been washed. The measurementmethod is the same as that of the clothes monitor. Asorting machine provided at the rear of this unitseparates normal articles from contaminated articles.However, due to a different method of operation, thismonitor also supports the return of contaminatedarticles to the insertion site. Moreover, the belt used ishighly durable and compatible with wet articles. The

Table 3 Specifications of the clothing monitor

external appearance of the small article front monitoris shown in Fig. 8 and its specifications listed inTable 4.(3) Front monitor

This monitor inspects the contamination of un-washed clothes and the like that have been placed in astainless steel wire-mesh bucket (well area). Whenplaced into the bucket, measurement starts automati-cally and the result is displayed after a fixed-timemeasurement has been performed. An alarm is issuedif the articles are judged to be contaminated. Tosimplify decontamination, the bucket has been de-signed to be easily detachable. The entire monitor issmaller and requires less installation space than priormodels. The external appearance of the front monitoris shown in Fig. 9 and its specifications listed inTable 5.

5. Whole Body Counter

5.1 OverviewIn order to determine whether radiation workers

who work inside a controlled area have internalradioactive contamination and to ascertain the inter-nal radioactive mass necessary for qualitative andquantitative analyses and for computation of thecommitted effective dose equivalent (internal exposure

Item Description

Radiationdetected Beta-rays


Detectionsensitivity

1.0 Bq/cm2 or less (radiation source : 60Co)0.37 Bq/cm2 or less (radiation source : U3O8)

Processingcapability

Approx. 250 (or more) articlesof clothes per hour

Size Approx. 1,350 (H)×1,000 (W)×2,500 (D) (mm), not including projections

Mass Approx. 3,000 kg


Fig.9 Front monitor

Table 5 Specifications of the front monitor

Fig.8 Small article front monitor

Table 4 Specifications of the small article front monitor

dose equivalent), a whole body counter (WBC) exter-nally measures gamma-rays emitted from radioactivematter within the human body.

5.2 Features(1) Measurement system that suits the objective

The measurement to determine the presence ofcontamination in the body is known as screening, andthe measurement implemented after internal contami-nation has been detected is known as precise measure-ment. Accordingly, Fuji Electric manufacturers both aWBC for screening use and a WBC for precisemeasurement use.

Specifications of bed-types of the WBC for screen-ing use and the WBC for precise measurement arelisted in Tables 6 and 7, respectively.(2) Types

WBCs are categorized as either bed-type or chair-type, according to the position of the subject beingmeasured. With the bed-type WBC, the subject lies ona bed and measurement is implemented by moving thebed inside a shield. With the chair-type WBC, thesubject sits on a chair inside an open-type shield and ismeasured. Additionally, in some cases a sealed-typeshield that encloses the entire room with 200-mm-thick steel plates is used. At the entrance/exit, either adoor or a maze configuration is employed. WBCs arecharacterized by low BG and the capability for precisemeasurement.

The external appearance of these WBCs are shownin Figs. 10 and 11.(3) Concern for the subject being measured

The subject must be tested while inside a shielded

Item Description

Radiationdetected Gamma-rays



1.0 Bq/cm2 or less(moving speed : 100 mm/s, radiation source: 60Co)

Processingcapability Approx. 250 (or more) undergarments per hour

Size Approx. 1,420 (H)×950 (W)×2,500 (D) (mm)


Item Description

Gamma-rays

Detector NaI (Tl) scintillation detector

Detectionsensitivity 37 Bq/cm2 or less (radiation source: 60Co)

Processingcapability

300 or more kg/h (evaluated at 5 kg per collection bag, and process time of 60 s/cycle)

Approx. 1,000 (H)×800 (W)×950 (D) (mm), not including projections


Radiationdetected

Size

Table 7 Basic specifications of the whole body counter forprecise measurement

Table 6 Basic specifications of the whole body counter forscreening measurement

Plastic scintillation detector or NaI scintillation detector

Shadow shield method (bed type)

30 s to 20 min

0.1 to 2.0 MeV

Approx. 2,500 to 4,000 m-1 (30-minute measurement)

Detector

Shielding method

Measurement time

Energy range

BG value

Detector sensitivity Approx. 150 to 250 Bq (137Cs)Approx. 50 to 100 Bq (60Co)

High-purity germanium detector or NaI scintillation detector

Shadow shield method (bed type)

Approx. 10 min

Approx. 2,500 to 4,000 m-1 (0.1 to 2.0 MeV: 30-minute measurement)

Detector

Shielding method

Measurement time

BG value

Detector sensitivity Approx. 150 to 250 Bq (137Cs)Approx. 60 to 90 Bq (60Co)


body, but guidance for the measurement is providedvia audible and displayed instructions so that thesubject does not become confused. Additionally, theshield is designed to be soft and to have smoothcontours so that it appears less intimidating.

Also, in some cases the showing of a movie duringmeasurement lessens the stress endured by the sub-ject. Fuji Electric is continuing to improve comfortduring testing.(4) Easing the burden on the operator

Processing, from the provision of measurementguidance until implementation of the measurement,can be automated and when measurement is complete,the measurement data can be transmitted to an upperlevel computer. This data is used in the WBCinspection performed when entering a controlled area.

The measurement results can also be stored in adata processing apparatus and verified on the displayscreen of that apparatus. The data processing appara-tus runs on a Windows*1 operating system to improve

visibility and simplify the process of verifying themeasurement results.

If the operator has an ID card, measurement canbe performed even during the nighttime hours or onholidays. This is a large factor in easing the burden onthe operator.(5) Support of diversifying data control methods

The data processing apparatus is provided with anend user computing (EUC) function, and in accordancewith the control, necessary data can be extracted anddisplayed on a screen.(6) Support of unmanned operation

In response to requests for laborsavings and tosupport unmanned operation, a network is utilized toshare input data effectively with an upper levelcomputer, and WBC inspection scheduling, the trans-mission of relevant measurement data among relateddepartments and companies and the like is system-atized. A system capable of unmanned measurementfor regular users is also pursued.

6. Hand-foot-clothes Monitor

6.1 OverviewThe hand-foot-clothes monitor is installed in con-

tamination inspection rooms at facilities that handleradioactive matter such as research laboratories, hos-pitals, and nuclear power plants, and detects thesurface contamination of radioactive matter that hasadhered to workers’ hands, feet, clothes and the like.The monitor detects beta-rays emitted from radioactivematter, and if the detected value exceeds a presetalarm level, the monitor sounds an alarm and displaysthe location of contamination on hands, feet or clothes.

The external appearance of the hand-foot-clothesmonitor is shown in Fig. 12 and its specifications listedin Table 8.

6.2 Features(1) Simply placing a hand or foot at the measurement

position will cause measurement to begin, thecontamination evaluated and the results displayedautomatically.

(2) The BG value is automatically measured at regu-lar intervals, and a subtraction calculation isperformed according to the latest BG value. Byreducing the effect of BG fluctuation, contamina-tion can be measured with greater accuracy.

(3) According the latest BG value, the detectable limitis computed and the measurement time is auto-matically adjusted so that contamination can bemeasured within a short amount of time.

(4) When contamination is detected, a color displaygraphically shows the location of the contamina-tion so that measurement results can be easilyverified.

(5) A plastic scintillation detector is used and, unlikea finite-life GM tube, does not require replace-

Fig.11 Chair-type whole body counter

Fig.10 Bed-type whole body counter

*1 Windows: A registered trademark of US-based MicrosoftCorp.


(10) The contamination-preventing film at the footmeasurement unit can easily be rolled up andreplaced.

(11) A printer is optionally available.

6.3 FunctionsThe two functions of BG measurement and con-

tamination measurement are performed repeatedly. Inthe case where the BG value has not yet beenmeasured, BG measurement is prioritized and per-formed for the preset number of times before contami-nation can be measured. Normally, BG measurementis performed and the value is updated to the latest BGvalue.

Contamination measurement falls into two catego-ries, hand-foot contamination measurement and cloth-ing contamination measurement, each of which isperformed independently. The hand-foot contamina-tion measurement begins when all hand-foot sensorshave been detected. After the measurement is com-pleted, the judgment results are displayed on a screen.The probe-shaped detector that is provided is used tomeasure clothing contamination while surveying thesurface of the clothes. Results are displayed on thescreen in real-time. In cases where results of thecompleted contamination measurement are abnormal,the BG verification setting function can be used tocheck whether the cause is due to the measurer’scontamination level or a monitor malfunction.

7. Conclusion

In the future, Fuji Electric intends to expand thismarket by: (1) developing equipment that supports therecent JIS standards established for surface contami-nation inspection equipment, and (2) developing lowcost equipment that is compliant with IEC standardsin order to expand sales overseas.

Finally, the authors wish to express their deepgratitude to the electric power companies and allindividuals who have provided guidance and coopera-tion.

Fig.12 Hand-foot-clothes monitor

Table 8 Specifications of the hand-foot-clothes monitor

ment.(6) The detector for measuring clothes contamination is

made of hard plastic and light in weight.(7) The low footboard is easy to step onto at the time

of measurement.(8) By using the rear wheels, one person can move the

monitor by himself or herself.(9) The monitor can be separated into three sections,

simplifying delivery and installation.

Item Description

Beta-rays

Plastic scintillation detector

1.0 Bq/cm2 or less (radiation source: 36Cl)0.2 Bq/cm2 or less (radiation source: U3O8)

15 s (can be set within range of 1 to 999 s)

Approx. 1,350 (H)×630 (W)×730 (D) (mm), or less

Radiationdetected

Detector


Measurementtime

Size

Mass Approx. 80 kg


Table 1 Main specifications of the internally-housed gammaray thickness gauge

Asao Monno

Industrial Measurement Instrumentsthat Use Radioisotopes

1. Introduction

Industrial measurement instruments that use ra-dioisotopes (RI) are instruments that harness radioac-tive rays to measure such parameters as thickness,level, density, moisture and the like. The advantage ofsuch measuring instruments is that they are non-contact, non-destructive and enable online, real-timehigh-speed measurements. Because the physical prop-erties of RI make these instruments less susceptible tothermal, electrical and vibratory noise sources, thesemeasuring instruments are widely used in such appli-cations as, for example, the mill control in a steelplant, or in production lines at chemical plants and inthe plastic and paper industries.

In addition to their use for product inspectionpurposes, these instruments also are used to produc-tion process control systems and have become estab-lished as special sensors essential to each productionprocess.

One such example is a hot steel plate thicknessgauge that operates automatically under supervisionfrom a process computer and transmits hot statethickness values, with a 50 ms response time, asoutput for the real time control of a mill, whilesimultaneously outputting and storing the thickness ofthe finished product, or in other words the cold statethickness value.

Fuji Electric offers a wide lineup of these instru-ments, including a gamma ray thickness gauge for usein steel plants, a beta ray thickness gauge for use withplastic and paper, various level gauges, moisturegauges, and the like.

This paper describes a thickness gauge to behoused inside a plate mill, a thickness gauge for hotseamless tubes, and Hitachi-compatible radioisotope-applied measurement instruments.

2. Gamma Ray Thickness Gauge Housed Insidea Hot Plate Mill

In the past, thickness gauges for hot plate millscould be installed only at a distance of at least 10 mfrom either the front or back of the hot plate mill.

The internally-housed gamma ray thickness gaugemeasures by irradiating gamma rays from inside themill housing, or more specifically, from the small gapbetween the rolls of the conveyor at a distance of 2 mfrom the center of the mill. Conducive to the earlyapplication of mill control, this gauge can be used atthe stage when the plate is still a slab of a considerablethickness. Furthermore, use of this gauge enhancesmill efficiency since there is no need to convey plates adistance of at least 10 m behind the mill in order toacquire mill control information.

In order to realize such a thickness gauge, inaddition to good environmental immunity performancecapable of withstanding the harsh environment insidea mill, namely, heat, mechanical shocks, copiousamounts of water, adhesion of iron scraps or ironoxides, falling pieces of iron and the like, because theinstallation site does not allow maintenance to beperformed offline, high reliability that differs qualita-tively from the reliability of conventional thicknessgauges, remote maintenance capability, or the likemust also be provided.

Details of the performance of the detector havebeen reported previously, and therefore, the descrip-tion below will focus on apparatus performance, sys-

137Cs 1.11 TBq

Plastic scintillator detector

Pulse amp method (digital count method)

Spectra stabilization by near-ultraviolet rays

735 m/s2 (75 G)

1/10 or less

Continuous operation possible inside a hot plate mill

Approx. 2 to 150 mm

Ex: 33 µm at 20 mm with 90 % reliability, 0.2 s response

5 µm / 8 h

Radiation source

Detector

Detector amp

Detector stabilizingmethod

Max. impact acceleration

Impact reduction ratio

Thermal resistance

Measurement range

Statistical noise

Drift

Instrument response 10 ms


tem configuration and maintainability.Main specifications of the internally-housed gam-

ma ray thickness gauge are listed in Table 1, and theconfiguration of a system currently being constructedis shown in Fig. 1. A 100 ms real time signal is outputfor mill control, and a fast 10 ms response signal isoutput to enable more detailed ascertainment of theplate profile. Thickness data is presented to the milloperator via a digital display and a plate profile imageis displayed in real time at each pass of the rollingprocedure, providing support for instantaneous deci-sion-making.

Remote maintenance, implemented while thegauge is online, uses internal samples to performautomatic multi-point calibration, which includes thezero point (see Published Japanese Patent No. H04-43207). This remote automated calibration, combinedwith the good stability of the detector, eliminates theneed for onsite maintenance of the instrument calibra-tion.

Furthermore, as independent processor is addition-ally provided to implement a preventative self-diagno-sis function which stores in a database various types ofmaintenance data for the detection and standby sys-tems, as well as real time measurements of vibration,impact, acceleration and the like, and supplies data forthe purpose of diagnosing and analyzing failure and toprevent trouble.

3. Tube Wall Thickness Gauge for Hot SeamlessTube Mills

Seamless tubes are high-strength steel tubes suit-able for use under severe conditions such as oil welldrilling. The tube wall thickness gauge for hotseamless tube mills is designed for mill lines, andespecially for mill control in a stretch-reducing mill(that reduces tube diameter and stretches tube wallthickness). This gauge is an automated measuringsystem that outputs wall thickness measurements in

Fig.1 System configuration of the internally-housed gamma ray thickness gauge

PL

PBL

Plate mill plant’s process computer

Terminal link

HMI for milloperator

Control panel for mill operator

Touch panel for maintenance

Display of plate profile, etc.

Computerwith 19-inch LCD

Standby systemStandby detector

Standby system’s gamma ray source

PIO Real time output : 100 ms

DDC for mill control

Main cabinet

LAN#1

LAN#2

LAN#3

HMD (Hot Material Detector)speed information, etc.

Gamma count, maintenance information (high voltage, temperature, vibration)

Gamma count, maintenance information (high voltage, temperature, vibration)

Detector

Gamma ray source

Chilled water system

Air

Air source for gamma ray shutter

Conveyor rolls inside mill

Internal samples

Acceleration sensor

Touch panel for control

Processor link

PrinterData handlingFA (Factory Automation) computer for HMI

Computer for remotemaintenance

FA computer for preventative self-diagnosis

Real time output : 10 msReal time output : 100 ms

Control panel

HMI : Human Machine Interface

Table 2 Main specifications of the tube wall thickness gaugefor hot seamless tube mills

137Cs 1.11 TBq, length 223 mm

Plastic scintillator detector with 350 mm measurement width

Pulse amp method(digital count method)

Spectra stabilization bynear-ultraviolet rays

Outer diameter : 25 to 180 mmWall thickness : 2 to 45 mm

Within 0.2 % of the wall thickness

0.2 µm / 12 h at 81 mm (outer diameter)and 9.21 mm (wall thickness)

Radiation source

Detector

Detector amp

Detector stabilizingmethod

Measurement range

Measurementaccuracy

Drift

Instrument response 8 ms


Fig.3 Mechanical part of hot seamless tube wall thicknessgauge

real time with a fast 8 ms response speed, whilesimultaneously determining the top and bottom cut-offlocations and storing wall thickness profile informa-tion.

As guidance to the mill operator, an image of thewall thickness profile is displayed in real time for eachpiece. The historical wall thickness profiles of anyarbitrary piece in the database can also be displayedupon request.

Table 2 lists the main specifications of the appara-tus under construction in FY2004, and Fig. 2 illus-trates its configuration. In addition, Fig. 3 shows theappearance of a conventional tube wall thicknessgauge, and Fig. 4 illustrates the measurement princi-ple of the hot seamless tube wall thickness gauge. Themeasurement principle avoids the introduction of mea-

suring error, even in the case where the position of thetube wall fluctuates horizontally or vertically duringthe course of motion (see Japanese Registered PatentNo. 1474136-00).

In order to realize this principle, not only must thegamma ray irradiation field be made uniform, but thedetector sensitivity must also be uniform. Thischallenge was solved by combining an approximately350 mm-wide plastic scintillator with a special lightguide that focuses the scintillation light uniformly andthen guides it to a photomultiplier. The electroniccircuitry is the same as that of the internally-housedgamma ray thickness gauge, and the near-ultravioletray reference method is used as the stabilizing method.

Utilizing two of these detectors, this apparatus

Fig.2 System configuration of the hot seamless tube wall thickness gauge

Fig.4 Measurement principle of hot seamless tube wallthickness gauge

Process computer for seamless tube mill

LAN

Speed signal

Main cabinet

FA computer for control panel HMI

Processor linkJunctionbox

Chilled water system

Speedsensor Hot tube wall

thickness gauge Localoperation panel

Air

HMI for mill operatorFA computerDisplay of wall thickness, etc.

Control panel for mill operator

LAN

Amount of gamma ray detection

Detector

Even if tube position fluctuates, amount of gamma ray detection does not change

Position fluctuation

Tube

Collimeter

Line radiation source


Fig.5 Hitachi-compatible radioisotope-applied measurementinstrument

realizes high count values and reduces statistical errorwith a fast 8 ms response speed.

4. Hitachi, Ltd.-Compatible Measurement Instru-ments

Fuji Electric manufactures and sells equipmentthat is fully compatible with Hitachi, Ltd.’s radioiso-tope-applied measurement instruments.

Not only is such measurement equipment inter-changeable on the system level, but compatibility isalso guaranteed on the component level for such basic

components as the radiation source container, detector,electronic circuitry, cables, accessories and the like,making it easy to implement partial equipment up-grades.

In particular, the source capsules, parts, drawingsand manufacturing processes of Fuji Electric’s andHitachi’s radiation source containers are completelyidentical. This is beneficial to the user for ensuringcompliance with the applicable laws and regulations.

Since the start of marketing activities under theterms of cooperation between Hitachi and Fuji Electric,these instruments have already been delivered toseveral tens of customers, and in all cases, theequipment is operating stably.

Figure 5 shows an example of a compatible instru-ment.

5. Conclusion

The internally-housed gamma ray thickness gaugeachieves better durability in terms of impact resistanceand thermal resistance than Fuji Electric’s previousthickness gauges, and also realizes stable mainte-nance-free operation, high-speed response, and a data-base function. In the future, Fuji Electric intends toapply these technologies to its entire line of thicknessgauges and to provide systems with even higher levelsof reliability.

Because the hot seamless tube wall thicknessgauge handles tube diameters of approximately 180mm, it is intended for rather large-scale systems. Inthe future, Fuji Electric plans to develop lower costequipment for smaller tube diameters or systemshaving simpler configurations.

Level gauges and density gauges are available bothas Fuji Electric models and as Hitachi-compatiblemodels. Future product development will promote theadvantages of each.

(a) Detector for gamma ray level gauge

(b) Radiation source container (shielding container)

Business Outline of the Each Operating Company

Company Business Outline

Fuji Electric Systems strives to inject new value into socialinfrastructure by offering industry-leading products and servicesin the industrial, public sector, energy, and transport fields. Asa solutions provider in the areas of information, the environ-ment, energy and services, Fuji Electric Systems works hand inhand with customers to make their businesses a success.

Fuji Electric FA Components & Systems supplies a range ofcomponents, as well as small and medium-sized systems usingthese components, to customers in the industrial automationfield. The company’s extensive array of products, which demon-strate world-leading levels of quality and performance, includeelectrical distribution control, drive, power electronics, motion,and human-machine interface (HMI) components and devices.Underpinned by this product portfolio and a lineup of relatedservices, the company is working to create new value forcustomers.

Leveraging its core competence —technological expertise— FujiElectric Device Technology offers high-quality, high value-addedproducts in the semiconductor, storage and imaging devicefields. The company’s ultimate goal is to create a range of world-leading products that satisfy customer needs for high-perfor-mance, compact and energy-efficient products in the industrial,automobile and information device fields.

Focusing on three core businesses: vending machines, whereFuji Electric has the leading share in the domestic market, cold-chain equipment, and coin & currency systems, Fuji ElectricRetail Systems is working to support society through thecreation of innovative and convenient retail spaces. The compa-ny also strives for maximum customer satisfaction by offeringnew solutions and services that enhance vending machineoperations and store management efficiency in many areas ofthe retail sector.

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FUJI ELECTRIC HOLDINGS CO., LTD.Erlangen Representative OfficeGERMANYTel : +49-9131-729613 Fax : +49-9131-28831FUJI ELECTRIC GmbHGERMANYTel : +49-69-6690290 Fax : +49-69-6661020FUJI ELECTRIC (SCOTLAND) LTD.U.K.Tel : +44-1355-234111 Fax : +44-1355-238810FUJI ELECTRIC FRANCE S.A.FRANCETel : +33-4-73-98-26-98 Fax : +33-4-73-98-26-99

ASIA

FUJI ELECTRIC HOLDINGS CO., LTD.China Representative Office (Shanghai)CHINATel : +86-21-6471-0897 Fax : +86-21-6471-4903FUJI ELECTRIC HOLDINGS CO., LTD.China Representative Office (Beijing)CHINATel : +86-10-6505-1263 Fax : +86-10-6505-1851FUJI ELECTRIC (SHANGHAI) CO., LTD.CHINATel : +86-21-6466-2810 Fax : +86-21-6473-3292FUJI ELECTRIC (CHANGSHU) CO., LTD.CHINATel : +86-512-5284-5629 Fax : +86-512-5284-5640FUJI GE DRIVES (WUXI) CO., LTD.CHINATel : +86-510-528-1932 Fax : +86-510-528-2052FUJI ELECTRIC DALIAN CO., LTD.CHINATel : +86-411-8762-2000 Fax : +86-411-8762-2030SHANGHAI FUJI ELECTRIC SWITCHGEAR CO., LTD.CHINATel : +86-21-5718-5740 Fax : +86-21-5718-1448

SHANGHAI FUJI ELECTRIC TRANSFORMER CO., LTD.CHINATel : +86-21-5718-5740 Fax : +86-21-5718-5745DALIAN FUJI BINGSHAN VENDING MACHINE CO., LTD.CHINATel : +86-411-8730-5908 Fax : +86-411-8730-5911DALIAN JIALE VENDING MACHINE OPERATION CO., LTD.CHINATel : +86-411-8596-2721 Fax : +86-411-8596-2732SHANGHAI GENERAL FUJI REFRIGERATION EQUIPMENT CO., LTD.CHINATel : +86-21-6921-1088 Fax : +86-21-6921-1066HANGZHOU FUJI REFRIGERATING MACHINE CO., LTD.CHINATel : +86-571-8821-1661 Fax : +86-571-8821-0550FUJI ELECTRIC (SHENZHEN) CO., LTD.CHINATel : +86-755-2734-2910 Fax : +86-755-2734-2912HONG KONG FUJIDENKI CO., LTD.HONG KONGTel : +852-2664-8699 Fax : +852-2664-8040FUJI ELECTRIC (ASIA) CO., LTD.HONG KONGTel : +852-2311-8282 Fax : +852-2312-0566FUJI ELECTRIC SYSTEMS CO., LTD.Taipei Representative OfficeTAIWANTel : +886-2-2561-1255 Fax : +886-2-2561-0528FUJI ELECTRIC TAIWAN CO., LTD.TAIWANTel : +886-2-2515-1850 Fax : +886-2-2515-1860FUJI/GE TAIWAN CO., LTD.TAIWANTel : +886-2-2556-0716 Fax : +886-2-2556-0717ATAI FUJI ELECTRIC CO., LTD.TAIWANTel : +886-3-321-3030 Fax : +886-3-321-7890FUJI ELECTRIC KOREA CO., LTD.KOREATel : +82-2-780-5011 Fax : +82-2-783-1707

East Asia

Southeast Asia

FUJI ELECTRIC SYSTEMS CO., LTD.Bangkok Representative OfficeTHAILANDTel : +66-2-308-2240, 2241 Fax : +66-2-308-2242FUJI ELECTRIC SYSTEMS CO., LTD.Jakarta Representative OfficeINDONESIATel : +62-21-572-4281 Fax : +62-21-572-4283FUJI ELECTRIC (MALAYSIA) SDN. BHD.MALAYSIATel : +60-4-403-1111 Fax : +60-4-403-1496FUJI ELECTRIC PHILIPPINES, INC.PHILIPPINESTel : +63-2-844-6183 Fax : +63-2-844-6196FUJI ELECTRIC SINGAPORE PRIVATE LTD.SINGAPORETel : +65-6535-8998 Fax : +65-6532-6866FUJI/GE PRIVATE LTD.SINGAPORETel : +65-6533-0010 Fax : +65-6533-0021

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