alara and occupational exposures: experience and challenges

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ALARA and Occupational Exposures: Experience and Challenges

J. Lochard

ISOE International ALARA SymposiumTsugura, Japan, 13-14 November 2008

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Content of the presentation

ALARA and the quest for reasonable : an historical perspective

From ICRP 60 to ICRP 103

Trends in occupational exposures

Radiation risk at the workplace in perspective

Concluding remarks

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First stage: prudence

Recognition of stochastic effects in the late 40s

"Taking into account uncertainties about the risk and the irreversibility of the effects, it is prudent to reduce exposures to the lowest possible level" (ICRP-1950)

The limit is not anymore a guarantee of the absence of risk

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Second stage : justification

In a context of uncertainty taking a risk is justified only if their is a benefit in return

If there is a benefit How far to reduce the risk without endanger the activity?

As low as practicable (ICRP 1-1958)

On which criteria to ground the decision?

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Third phase: economic and social considerations

Recommendation to keep exposures as low as readily achievable, economic and social considerations being taken into account (ICRP 9 -1965)

The reduction of risk must be compared with the effort to achieve it

Need of quantification for practical application

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ALARA: balancing costs and benefits

The adverb ‘readily’ is replaced by ‘reasonably’ (ICRP 22 -1973)

Introduction of the cost-benefit model

The decision process is reduced to a

few parameters and focused on the

avoided dose

Attempt to integrate social values in

the quantitative framework (ICRP 37-

1983)

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to reduce exposures

to the lowest

possible level

(ICRP, 1950)

to keep exposures

as low as practicable (ICRP 1, 1958)

to keep exposures

as low as readily achievable

economic and social considerations being taken into

account

(ICRP 9, 1965)

to keep exposures

as low as reasonably achievable

economic and social considerations being taken into

account

(ICRP 22, 1973)

to keep exposures

as low as reasonably achievable

economic and social factors being taken into account

(ICRP 26, 1977)

Evolution of the ALARA principle wording

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Beyond the cost-benefit model

ICRP 55 - 1988: Return to a more pragmatic approach: the ALARA Procedure

ICRP 60 - 1990: Need to consider "the magnitude of individual exposures, the number of people exposed and the likelihood of incurring exposures where these are not certain to be perceived (= potential exposures)"in the optimisation process

Equity issue and the tolerability of risk model

Introduction of the dose constraint concept for practices to limit the range of options considered in the optimisation process

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The tolerability of risk model

Unacceptable risk

Tolerable risk

Acceptable residual

risk

Dose limit

ALARA level

Individual dose level

Optimisation process

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ICRP 101- 2005: broadening the process

Optimisation of protection is a forward-looking process aimed at preventing exposure before they occur

Optimisation is a frame of mind always questioning whether the best has been done in the prevailing circumstances

Consolidation of the previous publications and broadening the process "to reflect the increasing role of individual equity, safety culture, and stakeholder involvement"

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The ICRP 60 system of protection (1)

Practices•Justification, optimisation, limitation (except for medical exposures)

•Dose limits•Individual dose constraints

Interventions•Justification, optimisation•Intervention levels

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Interventions

"generic" optimisation

Optimisation

Dose limit

Dose constraint Action/intervention level

Practices

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Planned exposure situations: situations involving the deliberate introduction and operation of sources.

• Justification, optimisation with dose constraints, dose limits (except medical exposures)

Emergency exposure situations: situations that may occur during the operation of a planned situation, or from a malicious act, or from any other unexpected situation, and require urgent action in order to avoid or reduce undesirable consequences.

• Justification, optimisation with reference levels Existing exposure situations: exposure situations that

already exist when a decision on control has to be taken, including prolonged exposure situations after emergencies

• Justification, optimisation with reference levels

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Planned exposure situations

Emergency and existing exposure situations

Optimisation

Optimisation

Dose limit

Dose constraint

Reference level

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The individual levels of protection

Dose limitsDose constraints and

reference levels

Protect individuals from public and occupational exposure…

from all regulated sources, in planned

exposure situations

from a source, in all exposure situations

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Dose ranges in ICRP 103 for dose constraints and reference

levels (1)Band of

constraint or reference

level

Characteristics

Greater than 20 to 100

mSv

Individuals exposed by sources that are not controllable, or where actions to reduce doses would be disproportionately disruptive. Exposures are usually controlled by action on the exposure pathways.

Greater than 1 to 20 mSv

Individuals will usually receive benefit from the exposure situation but not necessarily from the exposure itself. Exposures may be controlled at source or, alternatively, by action in the exposure pathways.

1 mSv or less

Individuals are exposed to a source that gives them little or no individual benefit but benefits to society in general. Exposures are usually controlled by action taken directly on the source for which radiological protection requirements can be planned in advance.

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Dose ranges in ICRP 103 for dose constraints and reference

levels (2)Band of

constraint or reference

level

Examples

Greater than 20 to 100

mSv

• Reference level set for the highest planned residual dose from a radiological emergency : 100 mSv

Greater than 1 to 20 mSv

• Constraints set for occupational exposure in planned situations• Constraints set for comforters and carers of patients treated with radiopharmaceuticals• Reference level for the highest planned residual dose from radon in dwellings• Reference level for existing situation resulting from accidents: residual dose of 1 mSv/year

1 mSv or less

• Constraints set for public exposure in planned situations

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The concept of dose constraint

The concept of dose constraint is used in conjunction with the optimisation of protection

A dose constraint is a source-related restriction on the individual dose from a source used prospectively in planned exposure situations which serves as an upper bound in the optimisation of protection from that source

The term “source” refers to any physical entity or procedure that results in a potentially quantifiable radiation dose to a person or group of persons

Dose constraints are defined at the design stage using past experience

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Constraints and planned exposure situations

Occupational exposure Usually set by operator

Small operators may need guidance from regulator

Transient/itinerant workers need special attention

Public exposure Usually set by regulator

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The tolerability of risk model

Unacceptable risk

Tolerable risk

Dose limit

Dose constraint

Individual dose level

ALARA level

Optimisation process

Acceptable residual risk

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Occupational exposure: number of monitored workers (UNSCEAR 2008)

Source 1975-79 1980-84 1985-89 1990-94 1995-99 2000-02

Number of monitored workers (thousands)

Natural radiation

6 500 11 550 11 550

Nuclear fuel cycle

560 800 888 800 670 660

Medical uses

1 280 1 890 2 220 2 320 2 442 2 592

Industrial uses

530 690 560 700 790 869

Military activities

310 350 400 420 378 331

Miscella.

140 180 160 360 476 565

Total 2 820 3 910 4 22811 100(4 600)

*

16 360(4 756)

*

16 567(5 017)

*

Miscellaneous: educational establishment, veterinary medicine, transport…* Without natural radiation (NORMs)

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Occupational exposure: annual collective dose (UNSCEAR 2008)

Source 1975-79 1980-84 1985-89 1990-94 1995-99 2000-02

Annual collective effective dose (man.Sv)

Natural radiation

11 700 27 500 27 500

Nuclear fuel cycle

2 300 3 000 2 500 1 400 1 000 800

Medical uses

1 000 1 140 1 030 760 803 850

Industrial uses

870 940 510 360 315 289

Military activities

420 250 250 100 52 45

Miscella.

70 40 20 40 53 56

Total 4 660 5 370 4 31014 360(2 660)

*

29 723(2 223)

*

29 540(2 040)

*


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Occupational exposure : annual average dose (UNSCEAR 2008 )

Source 1975-79 1980-84 1985-89 1990-94 1995-99 2000-02

Annual average effective dose (mSv)

Natural radiation

1,8 2,4 2,4

Nuclear fuel cycle

4,4 3,7 2,6 1,8 1,4 1,0

Medical uses

0,8 0,6 0,5 0,3 0,3 0,3

Industrial uses

1,6 1,4 0,9 0,5 0,4 0,3

Military activities

1,3 0,7 0,7 0,2 0,1 0,1

Miscella.

0,5 0,3 0,2 0,1 0,1 0,1

Total 1,7 1,3 1,00,8

(0,6)*0,8

(0,5)*0,7

(0,4)*


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Occupational exposure: distribution of individual doses

(ESOREX)

Dose range Medical Industry NPP NORM

< 0,1 353 553 44 953 45 324 762

0,1 - 0,2 22 450 6 066 11 375 591

0,2 - 0,5 36 288 5 824 16 843 1 190

0,5 - 1,0 31 194 4 709 7 973 2 551

1,0 - 2,0 11 549 3 267 6 197 11 188

2,0 - 5,0 7 333 5 962 11 073 10 714

5,0 - 10,0 2 058 1 369 1 529 653

10,0 - 15,0 928 1 412 1 545 80

15,0 - 20,0 311 104 141 32

20,0 - 50,0 384 53 45 23

> 50,0 30 8 2 0Study on Occupational Radiation Exposure of Workers in Europe, ESOREX 2005K. Petrova, G. Frasch, K. Schnuer, S. Mundigl

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Occupational exposure in the nuclear fuel cycle (UNSCEAR 2008)

Period

Monitored workers

(thousands)

Average annual

Collective dose (man.Sv)

Annual effective dose (mSv)

NR15

1975 - 1979

560 2300 4,4 0,63

1980 - 1984

800 3000 3,7 -

1985 - 1989

880 2500 2,8 0,42

1990 - 1994

800 1400 1,8 0,11

1995 - 1999

700 1000 1,4 0,07

2000 - 2002

660 800 1,2 0,07NR15: fraction of workers with effective dose higher than 15 mSv.

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Risk associated with ionising radiation

- Adult workers -

Detriment per sievert

Cancers 4.1 x 10-2

Heritable effects 0,1 x 10-2

Total 4,2 x 10-2

ICRP 103 (2007)

Assuming 25 years at work at the limit of 20 mSv the lifetime risk of developing a cancer is

increased by 2 %

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Occupational exposures in electricity generation (PWR)

PeriodMonitored workers

(thousands)

Annual Collective

dose (man.Sv)

Annual effective dose (mSv)

1975 - 1979

63 220 3,5

1980 - 1984

140 450 3,1

1985 - 1989

230 500 2,2

1990 - 1994

310 415 1,3

1995 - 1999

265 506 1,9

2000 - 2002

283 415 1,7Source: UNSCEAR 2008

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Annual risk associated with the average exposure in PWRs

Annual risk associated with 1.7 mSv (late cancer after exposure using ICRP 103 coefficient):

D = 1,7.10-3*4,2*10-2 = 7,14.10-5

Annual risk of lethal occupational accident (immediate death): France: 2.86.10-5 (2005), USA: 4.10-5 (2006).

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Detriment associated to radiation exposure and annual risk of fatal

occupational injury

0,0E+00

2,0E-05

4,0E-05

6,0E-05

8,0E-05

1,0E-04

1,2E-04

1,4E-04

1,6E-04

1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005

Risk of lethal work accident

0,0E+00

2,0E-05

4,0E-05

6,0E-05

8,0E-05

1,0E-04

1,2E-04

1,4E-04

1,6E-04

Detriment associated with ionising radiation exposure

Risk of lethal occupational accident in France Risk of lethal occupational accident in USADetriment associated with ionising exposure

3,5 mSv

3,1 mSv

2,2 mSv

1,3 mSv

1,9 mSv1,7 mSv

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Radiation risk in perspective

The average level of radiation risk in the workplace is in the same order of magnitude than other risks for workers

The upper exposure levels, particularly those close to the limits, are significantly deviating from the main trends as far as quantitative risk estimate is concerned

Need to pursue efforts to reduce further the exposure of the most exposed workers in all domains = systematic implementation of ALARA

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The way forward for further improvements in occupational

radiation protection Engaging a reflection on potential exposures (use of incident data basis)

Developing ALARA procedures and tools for dismantling operations

Sharing experience to diffuse the use of dose constraints

Enhancing radiation protection culture Strengthening existing ALARA networks Favouring stakeholders engagement in the decision making process

A remaining issue: the situation of transient workers

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ALARA and dismantling in France

The first dismantling operations at French nuclear installations and NPPs have shown:

A lack of ALARA culture, notably at the level of the formalisation of the process

A weakness of dose estimations for the preparation of the work

A lack of reactivity of the teams when the first data become available at the beginning of the operations

Missing records concerning the description of the installations and their life time history

The non adaptation of "classical" technical procedures used for operation and maintenance

The lack of commitment and engagement of all concerned parties

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The way forward for further improvements in occupational

radiation protection Engaging a reflection on potential exposures (use of incident data basis)

Developing ALARA procedures and tools for dismantling operations

Sharing experience to diffuse the use of dose constraints

Enhancing radiation protection culture Strengthening existing ALARA networks Favouring stakeholders engagement in the decision making process

A remaining issue: the situation of transient workers

alara and occupational exposures: experience and challenges

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