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
2 Outline
- Background
- Project Description
- Data
- Observations
- Concluding Remarks
3 Risk-Informed Decisionmaking Risk Information NUREG-2150
Background
4 Risk Information is Both Qualitative and Quantitative Risk {si, Ci, pi }
What can go wrong?
What are the consequences?
How likely is it?
- What can be done?
- What is the story?
Understanding Credibility, trust What can happen and why What probably wont happen and why Why we believe this
Background
5 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
Background
6 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)
- Technology = Methods, models, tools, data Project Description Not Quantitative Post-event critique (MMQB)
7 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)
Project Description Proprietary
8 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.
Data
9 Dataset Summary (50 Earthquakes, 1975-2019)*
Japan Outside 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.
Data
10 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
Observations
11 PRA Modeling: Human and Organizational Factors Manual Reactor Depressurization Operator Fails To Start/Control RCIC Injection Observations HFE = Human Failure Event
12 A Useful HRA Framework:
Integrated Human Event Analysis System (IDHEAS)
Observations
13 Selected Observations: Human and Organizational Factors Observations Macrocognitive Function Direct Effects (Seismic or Seismically-Induced Hazard)
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
14 Fire PRA and Fire/Seismic Interactions Observations Fire Prevention Rapid Detection and Suppression Safe Shutdown Fire Protection Defense-In-Depth Fire PRA Fire/Seismic Interactions (NUREG/CR-5088, 1989)
Fire Frequency Analysis Equipment Damage Analysis Plant
Response
Analysis
- Cable pulling
- Flammable liquid spills
- Flammable gas releases
- Fire spread from non-Cat I SSCs
- Suppression system failures
- Spurious suppression activation
- Degradation of fire recognition and fire fighting
15 Selected Observations: Seismic/Fire Interactions Observations Fire PRA Element Interaction Frequency Analysis Seismically-induced high energy arc fault (HEAF) due to differential ground subsidence (Kashiwazaki-Kariwa)
Seismically-induced HEAF due to shaking (Onagawa)
No other reported seismically-induced fires at NPPs Equipment Damage Analysis Failed transformer bushing leaked oil 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 Analysis No major shutdown complications due to seismic/fire interactions
16 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 Observations
17 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 Observations
18 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 Showed potential to develop useful lessons for HRA, seismic and fire PRA, and ATWS PRA analysis 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)