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
2 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
3 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
4 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
5 Incidents Reviewed External Floods*
- Hinkley Point, 1981
- Dresden, 1982
- Blayais, 1999
- Cruas, 2009
- St. Lucie, 2014 Storms*
- Turkey Point, 1992
- Maanshan, 2001
- Browns Ferry, 2011
- Pilgrim, 2013
- LaSalle, 2013
- Categories are not exclusive.
6 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 0400 Hurricane Andrew passed directly over Turkey Point, with sustained winds of 145 mph and gusts of at least 175 mph. Spurious alarms received for the spent fuel pool low level and instrument air pressure low.
7 Example: PRA-Oriented Review Category Sub-Category Summary Hazard Conditions Exceptionally strong storm (985 hPa; 180-200 km/h); high tide, storm surge, wind-driven waves at site.
Protection Dikes (5.7 m) insufficient height and inadequate shape, upgrade suggested by earlier study not done. Also, problems with detection and warning systems.
Onsite Impact
Fragility Safe Shutdown SSCs Exposed
Safe Shutdown SSCs Affected
Barrier SSCs Affected
Response
Functions Lost
Safe Shutdown Path
Recovery
Operator Actions
Other Incident Management
Offsite Impact
Long-Term Post-Event Changes (Plant)
Post-Event Changes (Fleet)
8 Observations: PRA Technology Confirmatory Multiple hazards Asymmetrical multi-unit impacts Less-than-extreme hazards Hazard persistence Failure of mitigation SSCs Failure of implicitly considered SSCs Warning times and precautionary measures HRA and emergency response complexities Less-Discussed Multiple shocks Scenario dynamics Geographical extent and potential for multi-site impacts
9 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
10 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
11 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