ML19210D835
| ML19210D835 | |
| Person / Time | |
|---|---|
| Issue date: | 08/04/2019 |
| From: | Nick Melly, Jose Pires, Nathan Siu, Frederick Sock, Jing Xing NRC/RES/DRA |
| To: | |
| Nathan Siu 415-0744 | |
| References | |
| Download: ML19210D835 (18) | |
Text
Qualitative PRA Insights from Seismic Events N. Siu , J. Xing, N. Melly, F. Sock, and J. Pires U.S. Nuclear Regulatory Commission Office of Nuclear Regulatory Research 25th International Conference on Structural Mechanics in Reactor Technology (SMiRT 25)
Charlotte, NC, August 4-9, 2019
- The views expressed in this presentation are not necessarily those of the U.S. Nuclear Regulatory Commission
Outline
- Background
- Project Description
- Data
- Observations
- Concluding Remarks 2
Background
Risk-Informed Decisionmaking NUREG-2150 Risk Information 3
Background
Risk Information is Both Qualitative and Quantitative
- What can go wrong?
- What are the consequences?
- How likely is it?
Risk {si , Ci , pi }
- What can be done?
- What is the story? -
What can happen and why What probably wont Understanding happen and why
- Why we believe this Credibility, trust 4
Background
Project Motivation
- PRA ethos: search for potential scenarios
- Empirical evidence: helps stimulate and temper imagination
- Examples:
- Fire incident reviews (NUREG/CR-6738)
- Post-Fukushima PRA-oriented analyses (PSAM 2013, PSAM 13)
- Exploratory analysis of storm and flooding events (PSAM 14)
- Hypothesis: analogous reviews of seismic incidents could be valuable to
- PRA developers and analysts
- Broader NRC efforts to increase/improve use of risk information 5
Project Description Project Objectives and Scope
- Objectives
- Identify seismic PRA technology* insights
- Provide educational experience for RIDM support
- Identify lessons for intelligent search tool development
- Scope
- Exploratory, qualitative study
- NPP incidents (not conditions)
- Focus on response (recognizing seismic community work on hazard and fragility)
Not
- Quantitative
- Post-event critique (MMQB)
- Technology = Methods, models, tools, data 6
Project Description Approach
- Team: varied experience levels with seismic engineering and PRA; supplemented (human factors, fire) based on early results
- Review considerations
- Chronology
- Hazard, fragility, plant response
- Principal data sources
- Public (e.g., LERs, ETH Zürich event database, papers, event and seismic PRA guidance reports, industry websites)
- IAEA Incident Reporting System (IRS)
- INPO Consolidated Event System (ICES) Proprietary 7
Data Dataset Characterization
- 50 earthquake events* (1975-2019)
- Vast majority are minor (little or no effect on plant operations)
- Some prior to operation or during shutdown; might have triggered a transient
- Minor events => little plant response information available
- Most information from
- July 16, 2007 Niigataken Chuetsu-oki earthquake
- March 11, 2011 Great East Japan earthquake
- August 23, 2011 Mineral (VA) earthquake
- Other notable events
- September 21, 1999 Chi Chi earthquake
- December 26, 2004 Sumatra-Andaman earthquake
- Foreshocks and aftershocks are not treated as separate events.
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Data Dataset Summary (50 Earthquakes, 1975-2019)*
Outside Japan Japan Earthquakes Earthquakes exceeding then-current OBE/SSE 3 7 Earthquakes with large aftershocks (Mw > 6)a 4 3 Earthquakes felt at multiple sites 7 9 Earthquakes causing at least one reactor trip 7 4 Reactor Effects Seismically-induced reactor tripsb 25 7 Seismically-induced complicated transientsc 12d 6 aSomewhat arbitrary value chosen solely for illustrative purposes.
bIncludes trips due to seismically-induced tsunamis.
cInvolves a reactor trip and potentially significant additional failures (e.g., partial or complete LOOP).
dEleven of these transients occurred on March 11, 2011.
- Table only characterizes our dataset.
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Observations General Observations
- Other than offsite power, no direct damage to major mitigating systems due to ground motion; major effects due to induced hazards (fire, external flood)
- Some reactor trips/safety system actuations for events with very low onsite PGAs
- If one unit affected, typically all units onsite also affected
- Some events affected multiple sites:
Impacts at Multiple Sites # Events Minimal response (e.g., triggered alert) or greater 10 Reactor trip 3 Serious challenge 1 10
Observations PRA Modeling: Human and Organizational Factors Manual Reactor Depressurization HFE = Human Failure Event Operator Fails To Start/Control RCIC Injection 11
Observations A Useful HRA Framework:
Integrated Human Event Analysis System (IDHEAS) 12
Observations Selected Observations: Human and Organizational Factors Macrocognitive Direct Effects (Seismic or Seismically-Induced Hazard)
Function Detection
- Loss of I&C (including seismic event detection)
- Spurious alarms
- Degraded/dangerous site conditions Understanding
- Likely minor effects for most events
- Fukushima Daiichi o Reduced situational awareness (lack of information) o Effects of mismatched expectations, extreme stress?
Decision Making
- Anticipation of future events (e.g., tsunami following EQ)
Action
- Onsite and offsite damage, debris, and other impediments
- Disruption due to follow-on alerts and aftershocks Teamwork
- Off-site center initially non-functional (seismic damage, loss of power, degraded telecommunications, staffing)
- Non-nuclear disaster management needs
- Disaster scale => involvement of multiple organizations 13
Observations Fire PRA and Fire/Seismic Interactions Fire Protection Fire Rapid Detection Safe and Suppression Defense-In-Depth Prevention Shutdown Fire Equipment Plant Fire PRA Frequency Damage Response Analysis Analysis Analysis Fire/Seismic Interactions
- Fire spread from non-Cat I (NUREG/CR-5088, 1989)
- Cable pulling
- Suppression system failures
- Flammable liquid spills
- Spurious suppression
- Flammable gas releases activation
- Degradation of fire recognition and fire fighting 14
Observations Selected Observations: Seismic/Fire Interactions Fire PRA Element Interaction Frequency
- Seismically-induced high energy arc fault (HEAF) due to Analysis differential ground subsidence (Kashiwazaki-Kariwa)
- Seismically-induced HEAF due to shaking (Onagawa)
- No other reported seismically-induced fires at NPPs Equipment
- Failed transformer bushing leaked oil Damage Analysis
- HEAF-induced fire affected entire switchgear cabinet
- Suspended dust => spurious fire detection alarms (operators expected)
- Dense smoke from HEAF hindered detection of fire location, subsequent fire-fighting
- Fire fighting affected by broken underground fire lines
- Coordination with offsite fire department hindered by road damage, possibly also by offsite needs Plant Response
- No major shutdown complications due to seismic/fire Analysis interactions 15
Observations Commentary: Seismic/Fire Interactions No major nuclear safety impacts observed but
- HEAFs can be safety-significant (2-hour station blackout, Maanshan, 2001)
- Review of 24 U.S. HEAF events (all non-seismic):
- Some root causes might be triggered or exacerbated by EQ
- Loose or degraded connections
- Foreign material
- Root causes might not be readily identifiable by non-targeted seismic walkdown
- HEAF-targeted preventative maintenance activities would likely be effective 16
Observations Reactivity Effects
- Neutron flux related trips
- Onagawa 1 (11/27/1993)
- Mw 5.8
- PGA 0.12 g (reactor trip setting 0.20 g)
- North Anna 1 and 2 (8/23/2011)
- Mw 5.8
- CAV marginally exceeded in one direction
- Momentary loss of power to Seismic Monitoring Instrumentation Panel; geometry changes cause under-moderation and oscillatory (but overall decreasing) flux profiles
- Kashiwazaki-Kariwa 7 (2007): Post-event inspection identified stuck control rod (inserted, could not be withdrawn)
- Potential for reactivity effects may not be widely appreciated in PRA community 17
Concluding Remarks
- Exploratory study reinforces value of
- Interdisciplinary analysis (multiple perspectives, gap coverage)
- Detailed information supporting interdisciplinary analysis
- 50 events reviewed likely cover most significant events relevant to U.S.
nuclear industry
- Potential implication for hazard and fragility communities: increase emphasis on
- Offsite effects
- Seismically-induced HEAFs
- Aftershocks
- Next steps
- Compare observations against latest PRA (seismic, fire, HRA) guidance
- Develop knowledge management and knowledge engineering (search tool) findings
- Finalize project report
- Consider follow-on activities (e.g., mining of condition reports, non-nuclear events) 18