IAEA International Atomic Energy Agency Radiation Sources in Industrial and Research irradiators...

IAEAInternational Atomic Energy Agency

Radiation Sources in Industrial and Research irradiators

Overview and Accidents

Day 6 – Lecture 1

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To understand the uses of research and industrial irradiators and the potential for accidents to occur with their use.

Objective

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• Beneficial uses of ionizing radiation.

• Categories of irradiation facilities.

• Need for an adequate radiation safety program

• Consequences of radiological accidents

Contents

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Beneficial uses of ionizing radiation in irradiators

• Sterilization of medical products (e.g. insulin syringes);

Used in more than 160 gamma irradiation facilities and over 1300 electron beam facilities (2003)

• Sterilization of blood products;• Sterilization of pharmaceutical products;• Preservation of foodstuffs (spices etc);• Eradication of insects;• Synthesis of polymers; • Irradiation of cell cultures for research purposes.

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Types of Irradiators

Gamma Irradiation Facilities

The total source activity in an irradiator may range from a few Terabecquerels (1012 Bq) to more than 100 Petabecquerels (> 1017 Bq).

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Types of Irradiators (cont)

An irradiator in which the sealed source is:-

Category I (gamma)

• and where human access to the sealed source and the volume undergoing irradiation is not physically possible in the designed configuration.

[IAEA Safety Series 107]

• is shielded at all times;

• completely enclosed in a dry container constructed of solid materials,

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Category II (gamma)

A controlled human access irradiator in which the sealed source is:-


• is fully shielded when not in use;

• and is exposed within a radiation volume that is maintained inaccessible during use by an entry control system.


• enclosed in a dry container constructed of solid materials;

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Personnel access door

Control panel

Source holder

Turntable

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Category III (gamma)

An irradiator in which the sealed source is:-


Sample or product

container

Product hoist cable

Demineralized water pool

app

rox

7 m

Source array

Source rod

• is shielded at all times,

• and where human access to the sealed source and the volume undergoing irradiation is physically restricted in the designed configuration and proper mode of use.


• contained in a water filled storage pool,

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Category IV (gamma)

A controlled human access irradiator in which the sealed source is:-


• is fully shielded when not in use;

• and is exposed within a radiation volume that is maintained inaccessible during use by an entry control system.


• contained in a water filled storage pool;

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2 m concrete shielding

Hoist cable

Source hoist cylinderAccess for source transport container

Product Conveyor

Shielding pool

Guide cable

Control panelSource array

(safe position)

Personnel access door

Source transport container

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Electron Beam Facilities

Category I

An integrally shielded unit with interlocks where human access during operation is not physically possible owing to the configuration of the shielding

IAEA Safety Series107 divides electron irradiation facilities into two categories.

Category II

A unit housed in shielded rooms that are maintained inaccessible during operation by an entry control system

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Electron Beam Facilities (cont)

Lead shieldProduct conveyor

High voltage transformer

Controls

Single stage electron beam source

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Electron Beam Facilities (cont)

Scan horn

Concrete shield

High voltage system

Oscillator cabinet

Access labyrinth

Product conveyor

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Accidents Need for an adequate radiation safety program

5 fatal accidents were reported to the IAEA between 1975 and 1994.

Deaths from exposure to radiation from irradiators

Incident 1 Dose Prime causes

1 to 4 minutes to

500 TBq 60Co

12 Gy to the bone marrow

• Untrained, unsupervised and unauthorized worker gained access to the irradiation cell

• The source had been left exposed

[Lessons learned from accidents in industrial irradiation facilities. IAEA, 1996]

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Need for an adequate radiation safety program

Deaths from exposure to radiation from irradiators (cont)


“Several minutes” to 2.43 PBq

60Co

22 Gy. Died 13

days later.

• Faulty GM monitor dismantled leaving only one non-redundant interlock safety system connected to the entrance door.

• Continued operation of the facility nevertheless was permitted by management.

• Operator failed to use a portable survey meter


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Death from exposure to radiation from irradiators (cont)


23 TBq 60CoThree workers exposed; one

died

8.3, 3.7 and 2.9 Gy. One death after 6.5

months

• Lack of regulatory control• No contact with persons

having radiation safety expertise

• Inadequate worker training• Key safety features were

not repaired. Some removed


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Death from exposure to radiation from irradiators (cont)


1 ½ - 2 mins to

12.6 PBq 60Co

10-15 Gy. Died 36

days later

• Faulty limit switch indicating “source down”; safety interlocks were by-passed

• Gamma monitor ignored (failed previously)• Management had not installed the shroud

recommended by the manufacturer to prevent product jamming.

• Operating instructions not in local language


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Need for an adequate radiation safety program (cont)

Electron irradiator accidents

Incident 1 Outcome Prime causes

420-2400 Gy to R hand;

3-290 Gy to R foot; 290 Gy to parts of R leg from 10 MeV

electrons

• Right arm amputated above elbow 138 days later

• Right leg amputated above knee 6 months later

Worker knowingly entered the room by an unauthorized method (under the door through which the conveyor passed) thus effectively bypassing interlocks


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Electron irradiator accidents (cont)


Exposed during maintenance procedures to

0.4-13 Gy/s over 1-3 mins from “dark current” from 3 MeV electrons.

• 4 digits of R and L hands amputated after 3 months

• Hair thinning after 2 weeks. No regrowth after 6 months

• Worker not aware of “dark current”

• Worker did not use any radiation survey meter

• Worker did not have personal dosimeter

• Untrained assistant


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Electron irradiator accidents (cont)


Hands in 15 MeV beam while adjusting an experimental

sample.Dose difficult to

estimate

R hand and 2 fingers of L

hand amputated 8-15 months

later

• Facility had no interlocks or warning signals (1991)

• A physicist (who was responsible for radiological protection) entered the irradiation chamber to adjust a sample.

• A co-worker activated the irradiator without checking.


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Major causes of radiological accidents

• Flaws in the initial design. Redundant and diverse safety systems could have prevented most accidents.

• Access barriers based on radiation activated interlocks had either not been installed, had been removed, or were easily defeated.

• When trying to resolve problems, personnel were tempted to circumvent barriers if they could be easily bypassed with ladders, by stooping or crawling, or by manipulating switches, using tape, etc. In several facilities, personnel had employed tricks to circumvent the safety systems.

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• Personnel involved in accidents generally failed to follow instructions to alert radiation safety supervisors when alarms indicated that the source was not in the safe “shielded” position.

Major causes of radiological accidents (cont)

• Personnel had usually failed to use a demonstrably operational portable radiation survey meter when entering the irradiation chamber. The incidents suggest that not following this obvious and simple safety precaution may be common practice. (Most operators involved in incidents also had not worn their personal monitoring device.)

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• In some incidents, management tolerated the removal or the defeat of radiation activated interlocks.

In at least one accident, management apparently approved the installation of a switch to bypass an interlock and the removal of the only passive detection system that could not be circumvented easily by stooping or crawling.


• Several accidents occurred after management had received the manufacturer’s recommendation to install a protective shroud that could have prevented the accident, but had failed to do so.

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• Many of the accidents occurred during shifts with only one trained worker on duty or on call. Employee behavior appeared to reflect a management policy of having one person undertake as many tasks and responsibilities as possible.


• Workers and operating personnel performed inappropriate actions based on available information and instructions given. In some cases, the personnel involved were not adequately trained to understand the hazards, or those who were trained made bad judgments

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Lessons learned from radiological accidents

• Diverse safety systems could have prevented most accidents.

• Safety is compromised if the facility is not carefully audited to identify conditions critical to safety.

This requires consideration of redundancy, avoidance of single mode failures and human factors.

Where these considerations were not adequately taken into account, unsafe conditions resulted.

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• The management of the operating organization can quickly lose control of the employees’ level of knowledge and performance unless systematic audits are conducted and frequent training is provided.

Lessons learned from radiological accidents (cont)

• Management practices or attitudes resulted in degradation of the safety systems and operating procedures. It appears that sometimes product and production costs took precedence over safety.

This was particularly evident when oversight from the Regulatory Authority was absent or weak.

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• Personnel involved in accidents sometimes lacked an understanding of the fundamental principles of the devices with which they were working. e.g. the cold discharge current for electron sources or the connection between a strong odor of ozone and the interaction of ionizing radiation with air.

Lessons learned from radiological accidents (cont)

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Prevention and remedial actions

If implemented, the following would greatly improve the safety performance of industrial irradiators and reduce thefrequency and mitigate the severity of accidents when they do occur.

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Funding Organizations

Organizations have provided funds for the installation of irradiators in developing countries in which the radiation protection infrastructure is not yet strong or in countries that are not sufficiently experienced in the licensing and inspection of irradiators

Prevention and remedial actions (cont)

• Such organizations must recognize their safety responsibilities and promote the development and implementation of radiation protection programs for irradiators

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Licensees:-

• are responsible for the operation of the irradiator and the security of radiation source(s) in accordance with the requirements of the legislation imposed by the Regulatory Authority;


• have primary responsibility for radiation safety.

Senior management must recognize the potential hazards associated with an irradiator’s operation and must exercise leadership in developing and maintaining a strong safety culture throughout the entire organization.

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Designers, Manufacturers, Suppliers and Installers


• should provide sufficiently detailed information for the development of local operational and maintenance procedures, to enable a hazard assessment to be carried out and for emergency instructions to be prepared.

• must provide safety information in the local language

• bear a primary responsibility for carrying out research, testing and examination to ensure the safe design and performance of facilities, equipment and systems.

IAEA International Atomic Energy Agency Radiation Sources in Industrial and Research irradiators...

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