ICRP’s Radon Initiative

Presented To:

National Mining Association (NMA)

/Nuclear Regulatory Commission (NRC)

Uranium Recovery Workshop Denver – June 18 & 19, 2014

Presented By:

Douglas B. Chambers, Ph.D

1

International Radiation Safety Regime

issues

levels

trends

ICRP Protection philosophy,

principles and units issues

effects

risks

ILO convention 115:

occupational

radiation protection

FAO/WHO

Codex Alimentarius Commission

(food contamination guides)

UN transport regulations for

radioactive material

implemented by

Member States

IAEA, WHO, ILO, FAO etc. -Safety standards

-Protection programmes

UNSCEAR

Scientific basis

recommendations

2

ICRP and Radon

1993 - ICRP Publication 65 Protection against radon-222 at

home and at work ( based on epidemiology).

2009 - Porto Statement

The ICRP issued a statement on radon which stated that the dose

conversion factor for radon progeny would likely double, and the calculation

of risk from radon should move to a dosimetric approach, rather than the

longstanding epidemiological approach.

The ICRP approved the formation of a new Task Group, reporting to

Committee 4, to develop guidance on radiological protection against radon

exposure.

2011 - ICRP PUBLICATION 115 — Lung Cancer Risk from

Radon and Progeny and Statement on Radon

20014 - Coming soon from C4- Radiological Protection against

Radon Exposure

3

ICRP’s New Approach

Currently ICRP uses a dose conversion convention

(DCC) to calculate effective dose per unit exposure to

radon progeny based on epidemiology.

The detriment adjusted risk coefficient for radon will

double.

Doses from radon and its progeny will be calculated

using ICRP biokinetic and dosimetric models.

Current dose conversion values may continue to be

used until new ICRP dose coefficients are available.

4

Epidemiology – a few comments

Currently based on relative risk models

Relative risk models depend on baseline

risk

Smoking is the major cause of lung cancer

Smoking prevalence is an important factor

in baseline lung cancer rates

5

Ratio of Risks of Age-specific Deaths

in Male Smokers/Non-Smokers

0

5

10

15

20

25

30

35

40

45-49 50-54 55-59 60-64 65-69 70-74 75-79 80-84 85+

Dea

ths

per

10

0,0

00

pers

on

-ye

ars

Age Group

Lung

All causes

Lung Cancer Mortality of Smokers vs.

Non-smokers

Overall Mortality of

Smokers vs. Non-smokers

Thun et al. (1997)

Age-Specific

Deaths

6

Smoking Prevalence (Country)

7

15

20

25

30

35

40

45

45

50

55

60

65

70

75

80

85

1979 1984 1989 1994 1999 2004 2009 2014

Pe

rce

nta

ge (

%)

Mo

rtali

ty R

ate

, C

as

es

per

10

0,0

00

Year

Lung Cancer Smoking Prevalence

Age-Standardized Mortality Rates and Smoking

Prevalence for Lung Cancer in Males, Canada 1983-2012

• Canadian Cancer Society Statistics (2012)

• Tobacco Use in Canada: Patterns and Trends , 2012 Edition

8

Epidemiological Results

Risk projection models are relative risk models

and characteristics of underlying populations

are important

Smoking is the dominant risk for lung cancer

ICRP 115 report notes risk is on the order of 20 times

greater for smokers vs. non-smokers

General trend of declining smoking rates

9

Key Environmental Factors

Total alpha activity.

Particle activity size distribution in the mine

atmosphere.

Fraction of unattached radon decay products.

10

Past Measurements

The major factor controlling the bronchial dose from

inhalation of 222Rn decay products is their associated

particle size (activity size distribution).

The decay products attach mainly to the ambient

particle distribution but a small fraction, mainly 218Po,

remain as small nuclei called the unattached fraction.

Activity size distributions in mines have not been well

measured, mainly because it is a difficult research area

and the instruments are mainly for laboratory use.

11

Experimental Setup

Saskatchewan Mine (Nov 1995) Keng Wu-Tu, Isabel M. Fisenne and Adam R. Hutter (EML 1997)

12

The attached radon progeny are associated with the accumulation

mode aerosol with activity median thermodynamic diameters

(AMTD) of 50 - 500 nm.

Diffusion batteries utilising tubes, parallel plates, porous carbon

or wire screens have all been used to measure radon daughter

activity size distributions in this size range.

Measurement of Activity

Size Distribution

Source: Solomon, July 2011

13

Behaviour of DCF with particle size is strongly affected by two sets of deposition processes following inhalation:

With size decreasing below 3 nm there is a dose reduction due to deposition losses in the nose;

Above 20 nm the dose decreases due to increased penetration into the lower respiratory tract.

Can match to DCF size behaviour using two wire screens, one for nasal deposition, the other respiratory tract collection.

“Effective Dosimeter” reads out directly in mSv/h.

ARPANSA “Effective Dosimeter”

Source: Solomon, July 2011

14

Aerosol Size Distribution

Radon daughter PAEC

particle size distribution

measured by ARPANSA

with combined 4-stage

serial graded screen array

and 5-stage parallel

screen diffusion battery in

an Australian diesel

operated underground

uranium mine

Olympic Dam).

Source: Solomon, July 2011 (based on 1995 study)

15

Field Sampling Requirements The need for, easily deployable, and relatively portable

instrumentation.

The need for small, robust, reliable flow controllers for the

sampler.

The need for continuous flow measuring equipment for the

sampling instrument.

The need for low background, high efficiency alpha counting

equipment for the measurement.

The need for a reliable deconvolution program for data

reduction that records the error for the derived size

distributions.

The need for size distribution validation, i.e., quality control,

for the sampling equipment. Inter comparison exercises are

important.

16

Available Instrumentation

for Particle Size Measurements Cascade Impactors: rely on change on air velocity directed

through sequential plates.

Mobility Analyzers: depend upon differing electrical mobility

for particle size separation.

Graded Screen Arrays: Graded screen arrays (GSA) use the

same air flow rate through screens of different mesh size, usually

60 to 600mesh. The size separation is based on differing diffusion

coefficients with diameter.

Multi element: e.g., NYU (Harley’s) IMP with an inlet impactor,

that collects on a ZnS disk for direct counting, followed by 4 fine

mesh screens (GSA) and an exit Millipore backup filter to capture

all residual particles

17

Measurement Issues

Variability (mine to mine, within mine, change with

time).

Technical feasibility (e.g. instrumentation).

Operational (level of effort, suitable locations,

frequency).

Administrative (incorporate into dose estimation

protocol, national dose registry based on

measurement of WLM and estimates of WLM).

Interpretability/consistency for compliance with

national regulation.

18

Measurement Protocol

No “standard” protocol is currently available

A protocol is needed to ensure comparability

and interpretability of results across mines and

countries

Protocol needs to consider variability of mine

atmosphere

19

Dosimetric Models

20

ICRP’s 66 HRTM, will be the basis for

radon progeny conversion factors

Radiation dose from inhaled radon

progeny depends on deposition site

within the respiratory tract

Lung cancer from RDP is associated

with radiation exposure to the

bronchial region of the lung

This is dependent on the size of the

radon progeny particles

Estimated doses depend on the

physical model and numerous

assumptions

ICRP66 Human Respiratory

Tract Model

21

Dose Modelling

Dose modelling has been performed for the

selected ranges of environmental parameters.

The dose modelling has been performed by UK

HPA using the HPA’s implementation of the

ICRP’s HRTM model.

22

Monodisperse aerosol (i.e. GSD = 1.0)

with unit density (ρ) and shape factor (χ),

HPA (August, 2012)

0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

0.1 1 10 100 1000 10000

Do

se

( m

Sv p

er

WL

M)

Particle size (nm)

Effective and tissue weighted lung dose

Tissue weighted lung dose

Effective dose

Series3

10 mSv/WLM

23

Effective Dose

Absorbed dose to relevant tissue (model and

assumption dependent)

Alpha radiation weighting factor (wR)

[20 default, 10 lung cancer]

Tissue weighting factor (wT) [nominal

averaged over age and sex; and smoking

characteristics of ICRP 103 populations

[lung (0.12) and bronchial (0.08)]

24

Dosimetry and Smoking

The current ICRP dosimetry model (HTRM, ICRP 66)

indirectly considered smoking through wT,

A recent paper by Baias, et al. (2010) has calculated

dose conversion factors (mSv/WLM) for four different

categories of smokers taking account of the thickening of the mucus layer ( 2 fold decrease in dose factor)

impaired mucociliary clearance (a 2 fold increase in dose factor)

Calculations of Baias et al. partly account for physical

effects of smoking but epidemiology suggests a much

larger (10 fold) range of risks than those reported by

Baias et.al Biology considerations are important

25

Radon Dose Conversion Ranges 25

20

15

10

5

0

DC

C (

mS

v/W

LM

)

Occupational

Public

Occupational

Public (BEIR VI)

(French/Czech)

(ICRP 65)

Tomasek

-Occupational

(2008)

Epidemiology

ICRP

(11/07/2010)

ICRP 65

(1993)

LEGEND:

Heavy Long-Term Smoker

Never Smoker

Heavy Short-Term Smoker

HLT

NS

HST 21

(50% Smoker)

1 (Non-Smoker)

6-7 (Median)

Effect of Smoking

Epidemiology

SENES (2011)

21.1 Home

20.9 Mine

(Tomasek et al 2004)

6.4 Indoor

(ICRP 50)

Dosimetry

Table B.1

ICRP 115 (2010)

13.34 HLT

1.74 HST (2)

Dosimetry

Baias et al

(2010)

7.2 NS

26

Some of the Issues in Mines

All miner epi studies to date have used WLM as measure

of exposure

WL and WLM are common metric world-wide

There are well established protocols for measuring

“dose” by WLM

Uranium miners are well monitored and assigned

exposures in WLM

Modern exposures are low

The WLM is well recognized as a factor representing the

“notional” risk of lung cancer and current regulations

are based on meeting WLM limits

27

Some of the Challenges

Very Limited relevant data on mine aerosols

Currently technical and operational challenges for

making measurements in mines

Mine environment conditions are variable (mine to

mine, within mine, change with time) – challenge to

interpret mine levels to exposure

No measurement protocol currently exists

A possible wide range on Dose Conversion Factors

represents challenges for interpretability/consistency

for compliance with national regulation

etc.,

28

Questions ?

29