Nuclear Damage Compensation and Decommissioning Facilitation Corporation

NDF Approach to Risk Assessment
for Fukushima Daiichi NPS
April 11, 2016
Kazuki Hida
Nuclear Damage Compensation &Decommissioning Facilitation Corporation©Nuclear Damage Compensation and Decommissioning Facilitation Corporation

Strategic Plan & Risk Assessment
 NDF’s fundamental policy for decommissioning of FukushimaDaiichi NPS (1F) To reduce continuously and promptly the radiological risks
that resulted from the accident
 Strategic Plan is to design the mid- to long-term risk
reduction strategy
 Risk assessment in 2015 Strategic Plan Identified primary risk sources• Fuel debris, spent fuel, contaminated water, waste
 Prioritized through qualitative risk assessment• Hazard potential– Radioactive inventory and physical form
– Three-grade assessment• Likelihood of containment loss
– Integrity of containment– Three-grade assessment
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Result of Qualitative Risk Assessment
 Prioritized primary risk sources

Hazard potential

Fuel debris

Fuel inpool

To be addressed
To be addressed
as soon as
safely, effectively &practicableContaminatedcarefully withthorough preparation
water
Used& technologies toin buildings,realize more stable
Absorbenttanks andconditions
Columntrenches
To be addressed ona long-term basis
SolidWaste

Waste
SludgeLikelihood of containment loss

 Change in “Mid- to Long-Term Roadmap”
 Speed oriented  Risk reduction oriented
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Risk Management Process
Risk assessment
1. Risk identification: Find, recognize and describe risks(Including risk sources, events and consequences)

2. Risk analysis: Understand nature of risk andestimate level of risk

3. Risk evaluation: Compare level of risk with risk
criteria to determine if risk is acceptable or tolerable

4. Risk treatment: Reduce level of risk (Remove risk
source, reduce likelihood or mitigate consequence)
JIS Q 31000:2010 (ISO 31000:2009) Risk management – Principles and guidelines

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Terminology
Term*

General definition*

Example in Strategic PlanRisk

Effect of uncertainty on
objectives

Radiological effect on people andenvironment

Risk sourceIntrinsic potential to give rise
to risk

Radioactive materials

EventSeries of occurrence andchange in circumstances

Occurrence of earthquake etc.
and resulting change in risk
source and containment

Consequence

Outcome of an event with aneffect on objectives

Exposure to public or workers by
release of radioactive materials

Likelihood

Chance that something may
happenChance that exposure to public
or workers may happen

Level of risk

Magnitude of risk estimatedby combining consequenceand likelihood

Product of consequence andlikelihood

Risk criteria

Reference used to evaluate
the significance of risk

Comparison of risk with variousrisk sources or after treatment* JIS Q 31000:2010 (ISO 31000:2009) Risk management – Principles and guidelines

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Challenges towards Future Strategic Plan (1/2)
1. Risk identification
 Identification of risk sources• Characterization of various risk sources Identification of events and consequences• Requirements for degree of detail and achievability
2. Risk analysis
 Estimation of level of risks• Quantification of consequences and likelihoods under
uncertainty
3. Risk evaluation
 Purposes of risk evaluation• Acceptance or tolerability  Prioritization
 Determination of risk criteria• Relative comparison of level of risk with various risk
sources and after risk treatment
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Challenges towards Future Strategic Plan (2/2)
 Risk treatment
 Creation of options• A wide spectrum of potential options• Time dependence of risk for no action option
 Determination of metrics• Strategic Plan’s 5 guiding principles– Safe, proven, efficient, timely and field-oriented• Consideration of change in facility conditions and events
resulting from operation during treatment
 Selection of best option• Comparison of metrics between the options

 Requirements for risk assessment methodologies
Comprehensive

1. Risk identification
2. Risk analysis
3. Risk evaluation
4. Risk treatment

Quantitative

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Comprehensive Risk Assessment Methodology
 SED score: Safety and Environmental Detriment score
 Developed by U.K. Nuclear Decommissioning Authority (NDA) Used to inform prioritization of its nuclear facilities
Radiological Hazard Potential
 Radioactive Inventory Form Factor
 Gas, liquid, solid, etc.
 Control Factor
 Time the material could
be left without
monitoring/intervention

Safety Management
 Facility Descriptor
 Suitability of a facility tocontain the material
 Waste Uncertainty Descriptor
 Likelihood of deterioration ofthe material such that
retrieval will be more onerous

 NDF is customizing SED score to 1F with consultation from NDA
 Different risk sources and containment conditions than NDA’sfacilities
 Change in interpretation, addition or deletion of the factors

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Quantitative Risk Assessment Methodology
 Probabilistic Risk Assessment (PRA) methodology
 Risk analysis by event, likelihood and consequence Used to assess risks for operating and new power reactors
Initiating
event

Event 1

Event 2…

Success
Success
FailureOccurrence
FailureFinal state(No effect)

Success
Failure(No effect)
Likelihood & consequence
Likelihood & consequence NDF is developing the methodology adapted from PRA jointlywith U.S. DOE’s Pacific Northwest National Laboratory (PNNL) Uncertainty in condition of risk sources, event and likelihood
 Developing with generic information and expert judgement

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Concluding Remarks
 NDF’s mission is to design the risk reduction strategy forcontinuous and prompt reduction of the radiological risks in 1F
 Qualitative risk assessment was carried out for prioritizationin 2015 Strategic Plan
 Towards designing the future risk reduction strategy, new risk
assessment methodologies become necessary Comprehensive methodology for prioritization• Under modification of SED score with consultation fromU.K. NDA
 Quantitative methodology for risk treatment• Under development of the methodology adapted from
PRA in cooperation with U.S. PNNL Using these methodologies, the risk reduction strategy will be
designed and implemented into the future strategic plan
 Note that any decisions should be made not only with risk
information but with various considerations

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