The Swedish radiation protection standard for geological...
Transcript of The Swedish radiation protection standard for geological...
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