ML19156A484
| ML19156A484 | |
| Person / Time | |
|---|---|
| Issue date: | 06/11/2019 |
| From: | M'Lita Carr, Ian Gifford, Joseph Kanney, Nathan Siu, Zeechung Wang Office of Nuclear Regulatory Research |
| To: | |
| M. Carr 415-6322 | |
| Shared Package | |
| ML19156A446 | List: |
| References | |
| Download: ML19156A484 (11) | |
Text
Qualitative PRA Insights from Operational Events N. Siu, I. Gifford, Z. Wang, M. Carr, and J. Kanney U.S. Nuclear Regulatory Commission Office of Nuclear Regulatory Research Presented at 4th Annual Probabilistic Flood Hazard Assessment Workshop U.S. NRC Headquarters, Rockville, MD April 30 - May 2, 2019
Background
- Part of the PRA process involves searching for potential scenarios (What can go wrong?)
- Empirical evidence (operating experience) helps stimulate and temper imagination
- Example: 1975 Browns Ferry fire incident reviews (NUREG/CR-6738)
- Hypothesis - analogous reviews of other incidents could be valuable to:
- PRA developers and analysts
- Broader NRC efforts to increase/improve the use of risk information 2
Project Objectives and Scope
- Objectives
- Identify PRA technology* insights
- Provide educational experience for risk-informed decisionmaking support
- Identify lessons for intelligent search tool development
- Scope
- Exploratory, qualitative study
- Limited number of incidents
- Technology = Methods, models, tools, data 3
Approach
- General
- Review team with varied PRA experience levels and areas of interest
- Informal event selection, considering:
- Information availability
- Personal interest
- Review structure
- Chronological
- Hazard, fragility, plant response
- Principal data sources
- Publicly available (e.g., LERs, papers, technical reports)
- IAEA Incident Reporting System 4
Incidents Reviewed External Floods* Storms*
- Hinkley Point, 1981
- Turkey Point, 1992
- Dresden, 1982
- Maanshan, 2001
- Blayais, 1999
- Browns Ferry, 2011
- Cruas, 2009
- Pilgrim, 2013
- St. Lucie, 2014
- LaSalle, 2013
- Categories are not exclusive.
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Example: Chronological Review Date/Time Event or Step Description August 17 Turkey Point staff began tracking Tropical Storm Andrew in the control room.
August 21 Plant staff began implementing the Emergency Plan Implementing Procedure (EPIP), including moving equipment inside, tying down equipment, and preparing for storm surge. Equipment was moved from the Unit 3 diesel fuel oil tank, which did not have missile protection.
August 23 An Unusual Event was declared due to hurricane warning issued by the National Hurricane Center.
1800 Unit 3 began shutting down. Turkey Point operators estimated that it would take 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> to complete an orderly shutdown and wanted to stagger the shutdown on each unit by 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />.
There was concern over the main turbines and balance of plant supporting equipment being located on an open air deck (risking personnel if they needed to be outside). Unit 3 reached Mode 3 at 1940 and Mode 4 at 0213 on Aug 24th.
2000 Unit 4 began shutting down. Both units were kept in Mode 4, rather than Mode 5, to retain steam-driven auxiliary feedwater pumps as an option for removing decay heat. Unit 4 reached Mode 3 at 2245 and Mode 4 at 0405 on Aug. 24th.
August 24 Hurricane Andrew passed directly over Turkey Point, with sustained winds of 145 mph and 0400 gusts of at least 175 mph. Spurious alarms received for the spent fuel pool low level and instrument air pressure low.
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Example: PRA-Oriented Review Category Sub-Category Summary Exceptionally strong storm (985 hPa; 180-200 km/h); high tide, Conditions storm surge, wind-driven waves at site.
Dikes (5.7 m) insufficient height and inadequate shape, Protection upgrade suggested by earlier study not done. Also, problems Hazard with detection and warning systems.
Onsite Impact Safe Shutdown SSCs Exposed Fragility Safe Shutdown SSCs Affected Barrier SSCs Affected Functions Lost Safe Shutdown Path Recovery
Response
Operator Actions Other Incident Management Offsite Impact Post-Event Changes (Plant)
Long-Term 7 Post-Event Changes (Fleet)
Observations: PRA Technology Confirmatory Less-Discussed
- Multiple hazards
- Multiple shocks
- Asymmetrical multi-unit
- Scenario dynamics impacts
- Less-than-extreme hazards
- Geographical extent and
- Hazard persistence potential for multi-site impacts
- Failure of mitigation SSCs
- Failure of implicitly considered SSCs
- Warning times and precautionary measures
- HRA and emergency response complexities 8
Observations: Knowledge Management and Engineering
- Educational benefits
- Improved understanding of specific events and mechanisms
- Improved understanding of external hazards PRA modeling challenges
- Challenges for intelligent search tools
- Limitations with current event significance measures
- Limitations with analytics-based approaches
- Database concerns (e.g., errors, multiple sources, evolution over time, volatility)
- Need for multidisciplinary interpretation and analysis 9
Concluding Remarks
- Limited scope, exploratory study achieved project objectives
- Old events can still provide useful lessons
- Conservative PRA analysis assumptions can bound many observed complexities, but
- might mask important risk contributors
- might not motivate useful risk management activities (e.g.,
preparation for asymmetrical impacts)
- Follow-on activities (additional PRA-oriented incident reviews, event catalogs) are underway 10
Questions?
Additional information about the project can be found here:
http://psam14.org/proceedings/paper/paper_164_1.pdf NRC Agencywide Documents Access and Management System (ADAMS)
Accession No. ML18135A109 11