ML22319A075
| ML22319A075 | |
| Person / Time | |
|---|---|
| Issue date: | 11/16/2022 |
| From: | Siva Lingam Licensing Processes Branch |
| To: | |
| Lingam S | |
| Shared Package | |
| ML22319A085 | List: |
| References | |
| Download: ML22319A075 (24) | |
Text
Public Webinar to Share Risk Insights from the NRC Staff's High Energy Arcing Fault LIC-504 Assessment November 16, 2022
2 Objectives Consistent with the NRC's Principles of Good Regulation and our Be RiskSMART framework, NRC staff will be sharing risk insights from the NRC's regulatory response associated with the evaluation of High Energy Arcing Faults (HEAF).
- Openness Transparent and publicly available information on our evaluations and analysis.
- Clarity Staff's evaluation considered a sample of sites with different design characteristics to understand generic implications to the fleet.
Characteristics were chosen to improve realism to support analysis and gather risk insights that could benefit the overall fleet.
Risk insights can significantly vary based on site, plant design and configuration, and plant operating characteristics.
Public Meeting on Risk Insights Associated with HEAF
Agenda Time Topic Speaker 1:00pm Meeting Kick-Off S. Lingam - 5 mins 1:05pm Opening Remarks M. Franovich - 10 Mins 1:15pm LIC-504 Assessment R. Rodriguez - 15 mins 1:30pm NRC Risk Insights S. Weerakkody - 15 mins 1:45pm Industry Remarks Duke Energy - 15 mins 2:00pm Industry Remarks Constellation - 15 mins 2:15pm Break 15 mins 2:30pm Panel Discussion Industry/NRC - 45 mins 3:15pm Public Comments NRC/Public - 30 mins 3:45pm Adjourn 3
Public Meeting on Risk Insights Associated with HEAF
4 LIC-504 Process Mike Franovich Director Division of Risk Assessment Office of Nuclear Reactor Regulation US NRC Public Meeting on Risk Insights Associated with HEAF
5 Refresher - Integrated Decision-Making Process for Emergent Issues (LIC-504)
- Developed as a lessons learned from Davis-Besse reactor vessel head degradation
- Provides a structured process and expectations to document decisions for issues that may warrant safety orders
- Provides guidance to apply integrated decisionmaking including risk, defense-in-depth, and safety margins considerations
- Has been used frequently for a range of emergent plant-specific and generic issues
- Not a substitute for other NRC processes Public Meeting on Risk Insights Associated with HEAF
6 2
3 4
5 1
Use performance measurement strategies to monitor the change Proposed increases in risk are small and are consistent with the Commissions Safety Goal Policy Statement Maintain sufficient safety margins Change is consistent with defense-in-depth (DiD) philosophy Change meets current regulations unless it is explicitly related to a requested exemption or rule change Integrated Decision-making (RG 1.174)
Radiation exposure to plant workers Enterprise Risk Be RiskSMART framework Factors Considered in LIC-504 Implementation 6
Public Meeting on Risk Insights Associated with HEAF
7 10-6 10-3 10-5 10-4 LIC-504 Graded Recommendations - Examples Change in CDF Regulatory Intensity 10-7 Weigh a Spectrum of Regulatory Options Immediate regulatory action - compensatory measures Formal backfit analysis ( 10-4) 50.54(f) letters Bulletin Information Notice/Outreach Smart inspection samples -
within baseline program No Actions Use RIDM -
Not numbers alone Public Meeting on Risk Insights Associated with HEAF
Public Meeting on Risk Insights Associated with HEAF 8
Reinaldo Rodriguez Reliability and Risk Analyst Division of Risk Assessment Office of Nuclear Reactor Regulation US NRC LIC-504 Assessment
HEAF LIC-504 STEP 1 - NO IMMEDIATE SAFETY CONCERN STEP 2 - DETAILED EVALUATION USING DRAFT METHODOLOGY Public Meeting on Risk Insights Associated with HEAF 9
Scope Copper and aluminum HEAF zones of influenceshould be treatedthe samebased on the current state of knowledge.
The LIC-504 assessment was then focused on examining the change in estimated HEAF risks associated with the use of the new HEAF PRA methodology.
Public Meeting on Risk Insights Associated with HEAF 10
Work Completed Visited one BWR and one PWR Assistance provided by each reference plant licensee was essential and added credibility and realism to the team's analyses The team generated risk-informed insights and recommendations Publicly available memo with WG recommendations was issued on July 22, 2022 (ADAMS Accession No. ML22201A000).
Public Meeting on Risk Insights Associated with HEAF 11
Staff Insights Public Meeting on Risk Insights Associated with HEAF 12 THE RISK OF HEAF COULD BE HIGHER OR LOWER THAN CALCULATED UNDER THE PREVIOUS METHODOLOGY RISK COULD VARY SIGNIFICANTLY BASED ON PLANT CONFIGURATION FOR CERTAIN CONFIGURATIONS, THE ESTIMATED RISK FROM NON-ISO-PHASE BUS DUCTS COULD BE NOTABLY HIGHER THAN PREVIOUSLY MODELED CONCLUDED THERE IS NO SIGNIFICANT INCREASE IN TOTAL HEAF RISK, THAT WARRANTED THE NEED FOR ANY ADDITIONAL REGULATORY REQUIREMENTS
Recommendations Public Meeting on Risk Insights Associated with HEAF 13 Information Notice Issue Risk insights into NRRs ongoing PRA configuration control initiative.
Incorporate Integrating risk insights into NRRs inspection program in accordance with ROPs change control processes.
Consider Risk insights with internal and external stakeholders.
Communicate
Next Steps Public Meeting on Risk Insights Associated with HEAF 14 Info Notice Information Notice (Winter 2022)
Complete Supporting technical assessments (RES/EPRI)
(December 2022)
15 Sunil Weerakkody Senior Level Advisor Division of Risk Assessment Office of Nuclear Reactor Regulation US NRC Public Meeting on Risk Insights Associated with HEAF NRC HEAF-Related Risk Insights
16 Be clear about the problem Public Meeting on Risk Insights Associated with HEAF
17 Use of Teaching and Managing Elements to Generate Recommendations During LIC-504 Review What are the risk insights that could enhance plant safety?
Public Meeting on Risk Insights Associated with HEAF
18 Sources of Operating Experience: IN 2017-4 and NEA/CNIR(2013)(6) 48 HEAF events described in the OECD report entitled Fire Protection Topical Report No. 1, Analysis of High Energy Arcing Faults, June 2013.
Six HEAF events are discussed in NRC Information Notice (IN) 2017-04, High Energy Arcing Faults in Electrical Equipment Containing Aluminum Components, August 2017.
HEAF events, even those that are not initially risk significant have the potential to cause subsequent failures due to explosion effects, smoke, and ionized gases. These subsequent failures can create a chain of consequential events that could pose special challenges to operators.
Therefore, public health and safety and enterprise risk is best served by increased focus on preventing HEAF events (as opposed to mitigation).
Public Meeting on Risk Insights Associated with HEAF
19 Sources of Operating Experience -
HEAF Event at Maanshan Nuclear Power Plant NRC report entitled, Operating Experience Assessment: Energetic Faults in 4.16 kV to 13.8 kV Switchgear and Bus Ducts That Caused Fires in Nuclear Power Plants
[NPPs]1986-2001, February 2002 (ADAMS Accession No. ML021290364) provides details regarding the Maanshan nuclear power plant HEAF event which is the most risk-significant (when Conditional Core Damage Probability is used as the metric) relevant to US LWRs.
HEAFs that can lead to SBOs are likely to initiate at buses or switchgear that are essential to supply alternating current power from both offsite power and emergency diesels (or other emergency supply).
Resources focused to minimize the likelihood of HEAF occurrence at those switchgear and buses (e.g., improved preventive and predictive electrical maintenance) can significantly reduce HEAF related risks.
Measures taken to minimize the possibility of a HEAF at one emergency bus, causing failure of the redundant electrical train, due to consequential failures (e.g., due to smoke, or design deficiencies), will also minimize the SBO related HEAF risks.
Public Meeting on Risk Insights Associated with HEAF
20 Sources of Operating Experience - NRC/RES Accident Sequence Precursor Database Plant/
Event Date (ADAMS Accession No.)
Risk Metric and Impact on Plant 1
Maanshan (ML021290364)
Fort Calhoun (ML12101A193)
CDP = 4x10-4 The issue was modeled as a degraded condition that considered the potential for common cause failures of other breakers associated with the degraded condition.
3 Robinson 3/28/10 (ML112411359)
CCDP = 4x10-4 Partial LOOP and potential loss of reactor coolant pump (RCP) seal cooling 4
Diablo Canyon, Unit 1 (ML20112H532)
Brunswick, Unit 1 (ML17109A269)
Waterford (ML20140A222)
Cooper (ML18068A724)
This event was evaluated as concurrent degraded conditions and, therefore, used a CDP as the metric.
8 Shearon Harris (ML20156A243)
CCDP = 4x10-6 Reactor and turbine trip 9
Turkey Point 3 (ML18038B063)
CCDP = 3x10-6 Loss of a 4kV Bus 10 Arkansas Nuclear One 2
,(ML15238B714)
CCDP = 2x10-6 Partial LOOP The ASP program evaluates potentially risk-significant events and degraded conditions that occur at US nuclear power plants (NPPs) and documents details of a subset of events that are characterized as accident sequence precursors in their database. These accident sequence precursors provide relevant risk-informed insights because they constitute the small subset of US HEAF events that were of relative high-risk significance.
Public Meeting on Risk Insights Associated with HEAF
21 Sources of Operating Experience - EPRI Report No. 3002015459, Critical Maintenance Insights on Preventing HEAF Maintenance of the Unit Auxiliary Transformer breakers is particularly important because their failure could lead to an extended duration generator-fed fault at the first switchgear bus. Operating experience has shown that this breaker is more likely to fail during automatic bus transfers.
For critical switchgear, such as feeder circuit breakers that carry higher currents, and switchgear that is part of a bus transfer scheme, proper maintenance of connections on both the bus side and the circuit breaker side is especially important.
Public Meeting on Risk Insights Associated with HEAF
22 Risk from all fire PRA scenarios HEAF Scenarios in Fire PRA Risk from HEAF Scenarios Risk from top three HEAF scenarios Risk from HEAF Scenarios Public Meeting on Risk Insights Associated with HEAF
23 Reducing Risk Associated with Risk-Significant HEAF Events, If They Occur In general, HEAFs leading to station blackouts (SBOs) constitute the highest HEAF related risks.
Therefore, effective use of plant design and operational changes that have been adopted to enhance the mitigation of beyond design basis accidents (10 CFR 50.155, Mitigation of beyond-design-basis events rule) are likely to reduce HEAF related risks.
Public Meeting on Risk Insights Associated with HEAF
Q&As and Comments Public Meeting on Risk Insights Associated with HEAF