The Swedish

radiation protection standard

for geological disposal

Mikael Jensen

Background - Mikael JensenBackground Mikael Jensen

Ph D Univ. of Lund - Cosmic Rays – particle track formation

Swedish Radiation Protection Authority: 1977 SSI Dosimetry (High LET)1980 SSI Emergency Preparedness (Post-TMI and

Chernobyl)Chernobyl)

1990 - SSI Waste Management

Rolf Sievert: SSI’s first Director General and – a unit

SSI and SKI merged 2009 to form the Swedish Radiation Safety Authority with responsibility for radiationresponsibility for radiation protection and nuclear safety

1 1 NPP illi i h bit t1,1 NPP per million inhabitants

45% of Sweden’s electrical energy

SFR - Operational waste

KBS-3KBS-3 (A separate presentation for KBS-3 will be presented later)

History of an emerging standardHistory of an emerging standard

Concepts in the standard– Risk

– Individual exposedIndividual exposed

– Longevity of the compliance period

Optimization and Best available– Optimization and Best available technology

HistoryThe concept of a standardThe concept of a standard

“Standard” does not exist in the Swedish legal framework (regulations do)

Regulations SSI FS 1998:1 now renamed SSM FS 2009:23).

It represents a standard for all radiation protection purposes

The non-quantitative aspect of f tsafety

Safety is a warm and fuzzy feeling !

The concept is open to i t t tiinterpretation

Technical Political A mixture of both in a gray area

History 1The 1977 “stipulation” act

Required a “completely” or “absolutely”Required a completely or absolutely safe disposal method (a condition for the fuelling of the reactor Ringhals 3)It looks naive today, since nothing is absolutely safe, but It was a first attempt in Sweden to applyIt was a first attempt in Sweden to apply the polluter pays, cradle-to-grave control and other important principlesp p p

Sub-system requirementsin standardsin standards

O l i l tOne example is pre-emplacement groundwater travel time (SKI, NRC)In Sweden additional conditions wereIn Sweden, additional conditions were given (as a basis for scientific discussion, not as regulations) that should be satisfied

Subsystem requirementsSubsystem requirements

1. low seismic activityy

2. low frequency of fractures and “deformation zones”

3. sufficient depth to avoid erosion

4. ground water composition, 7 < ph<9

5. temperature increase (as a result of the waste’s ti ) 40 °Cenergy generation) < 40 °C

6. impermeable rock, permeability k< 10-9 /s

7 low hydrostatic gradient I assumed =0 02 (MPa/m ?)7. low hydrostatic gradient I assumed =0.02 (MPa/m ?)

8. ground water travel time > 400 y

9 absence of valuable minerals9. absence of valuable minerals

History 2

The Swedish referendum after the TMI accidentaccidentafter considerable political debate - “unclear in nature for both spectators and those involved”nature for both spectators and those involved - it was decided that a positive vote would also imply that the requirements were fulfilled

People voted and – unknown to most voters –implicitly assessed the rock’s safety features

Observe:

Little international guidance available at the time (end of the 70ties)( )

Within ICRP acceptance of geological disposalWithin ICRP, acceptance of geological disposal was mainly considered a political issue

Difficult issues advised on 15-20 years laterDifficult issues advised on 15 20 years later– Techn. Bases for YM Standards (NAS 1995)

– ICRP 81 (2000) (some guidance in ICRP 46 - 1985)

The present Swedish radiation protection standardradiation protection standard

The work was influenced by the US Nat. Acad. Sciences report 1995. The NAS

Argued against subsystem requirements

Supported a standard using dose or risk (and preferred risk)

Emphasized the probabilistic aspect of future exposures

The Swedish standardThe Swedish standard

Individual risk per year < 10-6

p yThe required use of optimization and Best Available Technique, BATProtection of the natural environment, i.e. non-human species is requiredSome non-quantitative requirements are included relating to reporting of human intrusion scenariosintrusion scenarios

Most countries accept a dose standard in a certain sense

ICRP Publication 81 recommends a dose of less that 0 3 mSv per year implicitlyof less that 0.3 mSv per year, implicitly establishing a dose standard

Interpretation varies (possibly acceptedInterpretation varies (possibly accepted as one of many requirements)

Dose versus risk based regulations 1Dose versus risk based regulations 1“Risk” in IAEA’s Glossary

A multiattribute quantity expressing h d d h f h f lhazard, danger or chance of harmful or injurious consequences associated with actual or potential exposuresactual or potential exposures

Could be quantitative or qualitative

Dose versus risk based regulations 2

Risk – define it when you use it !!!

Technical Bases for Yucca Mountain Standards (the US National Academy of Sciences, NAS 95), glossary:

“In the context of this study, risk is probability of an individual receiving anprobability of an individual receiving an adverse health effect and includes the probability of getting the dose”p y g g

P(adverse effects) x P(getting the dose)

Dose versus risk based regulations 3

USNAS 95: Changes in the nominal risk/dose value may change the risk presented by the repository

Year ICRP publ. No. Total

1990 60 7.3 (~20%higher)

(Detriment-adjusted nominal risk coefficients for stochastic effects after

2007 103 5.7

(Detriment-adjusted nominal risk coefficients for stochastic effects after exposure to radiation at low dose rate, whole population, in 10-2 Sv-1, ICRP

publication 103, Table 1)

D i k b d l ti 4Dose versus risk based regulations 4is there a difference?

Type of standard Comment

Dose based Must take into account the probabilistic nature of exposure

D i k b d l ti 5Dose versus risk based regulations 5is there a difference?

Type of standard Comment

Risk based Well prepared for probabilistic p p peffects, but the

regulations forces regulator to search forregulator to search for

objective probability

The alpha and omega of riskp g

Scenario contaminants exposure adverse health effects

A Probability assumptions

Ω1 Ecological assumptions - who gets the dose?

(More generally accepted Ω2 Radiation protection assumptions)

The alpha and omega of riskp g

Al h f i k

Scenario – contaminants - exposure – health effects

Alpha of risk

The scenario probability, the issue of objective probabilitiesprobabilities

The Omega of risk

Issues likeIssues like

– who is at risk, where, with what habits and in what environment?

Al hAlphaProblems with probability in a standard

Probability of adverse effects from a dose

ICRP recommends probabilities as basesICRP recommends probabilities as bases for decisions in radiation protection,

not necessarily for description of absolutenot necessarily for description of absolute truth

(Personal commun. ICRP Chair L-E Holm)( )

This approach is more easy to acceptThis approach is more easy to accept

Problems with probability in a standard

Scenario probabilityWhat is the “starting probability of a

i ”?scenario”?

“The difficult communicability of the riskThe difficult communicability of the risk approach and difficulties in quantifying the entrance probability still limits the use of the risk criterion”risk criterion .

the German Reactor Safety and Radiation Protection Safety Committees (SSK 2002): “Die schwierige Vermittelbarkeit des ( ) gRisikoansatzes und die Schwierigkeit der Quantifizierung von Eintrittswahrscheinlichkeiten schränken die Verwendung von Risikokriterien jedoch ein”.

Problems with probabilityp yin general

Bruno de Finetti has used the mottoBruno de Finetti has used the motto “probability does not exist” Probabilities can, and has been defined by a , ynumber of axioms (Kolmogorov), but“Is there a property of the physical world that is in direct correspondence to the theoretical concept ofdirect correspondence to the theoretical concept of probability”? (Dawid)Radioactive decay perhaps qualifies, but – Decay is only a modest part of the safety analysis and – A single decay does not normally start a scenario

Specific probability-related problems

The clairvoyant test problemAss me e kne the fate of the repositorAssume we knew the fate of the repository throughout the compliance period – helped perhaps by a clairvoyant – no release occurred!The risk could still have been too high, perhaps from an earthquake that luckily didn’t occur –the implementer was then just being luckyt e p e e te as t e just be g uc yThe repository was OK but the risk was still above the regulatory limit!

Intergenerational risk distribution and “risk

Dose

distribution and risk dilution”

”Mean of peaks”

Dose

Annual risk

Conditional risk

Annual risk

Time (yrs)0One lifetime

SubjectiveSubjectivevs. objective i krisk

Subjective probabilityj p y

Consolidated mean subj. prop. density distribution (4 experts) No of earthquakes/100 km 100 ka

Mean of mean = 10 or

0,1 within 10 kmsubj. cumulative prop. distribution No of earthquakes within 100 km - 100 ka

Where is the objective probability?

Probabilities are easier to accept when derived from frequency but not necessarilyfrom frequency, but not necessarily

when input data exist only from analogue ( f fsituations (solubility of mineral A→ solubility of

mineral B)

when scaling up is not a simple process (scalingwhen scaling up is not a simple process (scaling of mean values is simpler than scaling uncertainties))

Comment on scenario probabilityComment on scenario probability

In the so-called safety/performanceIn the so called safety/performance assessment community, objective probability is hardly ever discussed As opposed to the reactor safety area (e.g. Apostolakis)See also NRC’s term “risk informed”See also NRC’s term “risk-informed”

Ω of riskΩ of riskBiosphere assumptions

The Brundtland commission’s definition f t i bl d l tof sustainable development

“development that meets the needs of the present without compromising the ability of future generations to meet their own needs”

Ω of risk 1Ω of risk 1Sustainable development A

(S di h t d d)(Swedish standard)

50 f l t b ll t “ t t ” th50 years of nuclear power cannot be allow to “saturate” the exposure of the site (1 mSv/y)

1 All sources originating from all time 1 mSv/y

2 One source (limited lifetime) → 1mSv/N(=10) = 0,1 mSv/y( ) ( ) , y

3 A repository over 100 000y → 0,01mSv/y

=10 µSv/y → 10-6

per year

Ω f i k 1Ω of risk 1Yearly risk burden

10 – 4 All sources (ICRP)10 All sources (ICRP)

10 510 – 5 1 source short time

10 ‐ 6 1 source 100 000 y

Ω of risk 2Ω of risk 2Sustainable development B

(S )(Swedish standard)

What is the probability of a person living at theWhat is the probability of a person living at the point of maximum release (and hence dose)?

The repository must allow for all types of possible ecosystems (biosphere in need of decisions, notecosystems (biosphere in need of decisions, not predictions)

Equal to requiring P(land occupation) =1Equal to requiring P(land occupation) 1

Ω f i k 3Ω of risk 3

Guidance on exposed test individual

ICRP

Publication 43: representative person

P blication 81 critical gro pPublication 81: critical group

Publication 101: representative person

The rationale behind this often presents problems: T Pigford took exception to the p g pother members’ view in the NAS group

Risk summation and completenesscompleteness

Probability of releases

Σ P(release scenarios)

An impossible question:An impossible question:

What is the probability that I p yforgot something important ?

Risk at the end of the day ( i k ti SR CAN)(risk summation SR CAN)

With some reservations

The length of compliance periodSome philosophical principles

We might wish for eternal safety, butThe impossibility to make a safety assessment over all eternity was a circumstance at hand at the time the practice was startedWaste management is not a free-standing practice. We have already taken the risks of our inability to make assessments in cosmic scale,

billi ( d f d d l )a billion years, (and a few decades lower)Conclusion:

It is too late now to ask for eternal safetyy

Human vs geological time scalesHuman vs. geological time scalesNo complete consensus on time scales

ICRP 81: 1000 to 10 000 yearsICRP 81: 1000 to 10 000 years

”... the risks associated with cataclysmic geologic changes such as glaciation andgeologic changes such as glaciation and tectonic movements may obscure risks associated with the waste disposal system

Geologists tend to favor long time periods

Optimization and BAT

In some cases (e.g. landfills) we may have confidence in risk calculated in the safety assessment. Risk may be sufficient for judging regulatory compliance

But we concluded that assessments for long lived waste in geological repositories suffer from g g pinevitable uncertainties. The risk criterion has therefore been complemented by Optimization and Best Available Technique BATand Best Available Technique, BAT

Optimization & ALARAOptimization & ALARA(As Low As Reasonably Achievable)

Old cost-benefit optimization from ICRP 27 (1977)R f (1977)

Optimization

Room for improvement

Improvements at great costs not justified

68

10

p not justified

Ref cost (10) + Cost of dose reducing

S10246of dose reducing

technique - “Dose reduction value” (0 1M$/Sv) 1 2 3 4 5 6 7 8 9 10

S1

Dose reduction

(0.1M$/Sv)

ICRP’s later formulation of optimizationICRP s later formulation of optimization

A more general formulation

Have I done all I can to reduce doses?

Th USNASThe USNASYM Report p 125

8 sentences on Optimization

USNAS - no stranger to optimization

The NAS recognizes that the multiple barrier requirement originates from the Nuclear Waste Policy Act of 1988.

Last optimization-related sentence on page 125:

The Swedish regulationsas explained in the guidance document

Optimization: Taking measures to limit doses p gand risk using risk calculations as a tool

Applying BAT: Taking measures to limit dose and risk by activities that may prevent, limit or delay releases from the repository's barriersdelay releases from the repository s barriers

Taking measures to limit doses and risk using riskdoses and risk using risk calculations as a toolNB reservations!

Summaryywe have:

L k d t th t f f t tiLooked at the concept of safety, sometimes a quantitative and sometimes non-quantitative concept –its regulation in Sweden

Been taking good advice where we can find it (NAS)

Seen the value of a (dose/risk) quantitative standard

Discussed elements in a standardDiscussed elements in a standard– Some theoretical limitations of risk

– Time scales

Optimization and BAT– Optimization and BAT

– The applications in a safety assessment report