ML12123A150
| ML12123A150 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 04/11/2012 |
| From: | Patrick Boyle Plant Licensing Branch II |
| To: | |
| Boyle P | |
| Shared Package | |
| ML12118A038 | List: |
| References | |
| TAC ME7750 | |
| Download: ML12123A150 (17) | |
Text
Risk Managed Technical Specifications Initiative 4b 1
SNC/NRC MEETING APRIL 11, 2012
Agenda 2
Introduction/Purpose Overview of the Project Technical Issues Discussion Meeting Summary and Action Item Review
Purpose 3
Purpose - Technical discussions on Vogtle pilot Risk Managed Technical Specifications (RMTS) program Treatment of SSCs unavailability included in the scope of 4b Treatment of Seismic Risk Desired Outcome - NRC comments and feedback on SNCs technical approach
SNCs Risk Informed Journey - Fleet 4
Achieve sustainable excellence through transitioning to risk-informed design and operation Improved safety Reduced forced outage rate Enhanced on-line and outage work planning Improved flexibility and regulatory predictability 4b is a key component in our quest of achieving operational excellence Be the change you want to see in the world Gandhi
SNCs Risk Informed Journey - Vogtle 5
Vogtle NRC Pilot for 4b - October 2010 NRC Commissioners Meeting - January 2011 Vogtle Seismic PRA Collaboration with EPRI - May 2011 Vogtle NRC Pilot for 50.69 - June 2011 4b Seismic/External Events treatment strategy submitted -
September 2011 Vogtle fire model peer-reviewed - February 2012 4b LAR - 3rd quarter 2012
Vogtle A4/4B Timeline 6
Enhanced A4 Procedure Changes/Training Initial LCO EOOS 4+ Fire PRA Peer 4B Vogtle LAR Selection Enhancement Review Submittal Mar 2011 Jun 2011 Sep 2011 Dec 2012 Mar 2012 Jun 2012 Sep 2012 Dec 2012 Mar 2013 Jun 2013 Sep 2013 EOOS Integrated 4B Procedure 4B Anticipated Fire + Internal Training NRC Approval PRA Model Key Changes Related to EOOS EOOS Ready for
- P6 to EOOS Automation Site-Specific
- CR Log to EOOS Automation Deployment for
- EOOS 4+ Enhancements Enhanced A4
Treatment of SSCs Unavailability in 4B 7
Final Safety Evaluation for NEI 06-09 requires the LAR to:
Justify any differences between TS functions and PRA functions success criteria Ensure LCO Conditions included are supported by CDF/LERF metrics Demonstrate treatment of SSCs unavailability impacted by LCO Conditions by concluding Has no impact on CDF/LERF Impact bounded by a surrogate SSC modeled in PRA, or Represented by a PRA a basic event(s)
Treatment of SSCs Unavailability in 4B is justified based on the following criteria that reflects the above NEI 06-09 guidelines
Treatment of SSCs Unavailability in 4B-Justification Criteria 8
Criterion 1: The SSC has no core damage or large early release risk impact Criterion 2: The SSC is not modeled in PRA, but the SSC can be directly correlated to a surrogate SSC included in the PRA Criterion 3: The SSC is added to the PRA model
Treatment of SSCs Unavailability in 4B:
Criterion 1 Example 9
Criterion 1: The SSC has no core damage or large early release risk impact Ventilation Systems SSCs TS LCO Condition Example One ESF room cooler and safety-related chiller train Inoperable ESF room cooler and safety-related chiller unavailability is not in PRA logic model because it does not impact CDF/LERF based on documented heat up analysis As a result, EOOS calculates a 30 day Backstop when ESF room cooler and safety-related chiller train become unavailable
Treatment of SSCs Unavailability in 4B -
Criterion 2 Example 10 Criterion 2: The SSC is not modeled in PRA, but the SSC can be directly correlated to a surrogate SSC included in the PRA Nuclear Service Cooling Water (NSCW) basins water temperature and/or water level TS LCO Condition Example One or more Nuclear Service Cooling Water (NSCW) basins with water temperature and/or water level not within limits.
Nuclear Service Cooling Water (NSCW) basins water temperature and/or water level unavailability is not in PRA logic model because it does not impact mitigation of CDF/LERF or has a negligible impact As a conservative assumption, for calculating RICT, impact on CDF/LERF assumes unavailability of Nuclear Service Cooling Water train as a surrogate in EOOS
Treatment of SSCs Unavailability in 4B -
Criterion 3 Example 11 Criterion 3: The SSC is added to the PRA model RWST Sludge system isolation TS LCO Condition Example:
One or more sludge mixing pump isolation valves inoperable.
Sludge mixing pump isolation valves unavailability is not in PRA logic model but the logic model was revised to include Sludge mixing pump isolation valves Impact of sludge mixing pump isolation valves unavailability on CDF/LERF is calculated by EOOS
Treatment of Seismic Risk 12 When a hazard group is not modeled in the baseline PRA, NEI 06-09 permits use of bounding analyses or other conservative quantitative evaluations to determine risk impacts.
Seismic Risk is not in the PRA for VEGP, and a Bounding Analysis approach is utilized for addressing Seismic risk impacts Internal Fire Seismic Other External Shutdown Events Risk Risk Risk Events Risk Risk Internal Fire Seismic PRA Events PRA PRA Bounding Updated (includes Internal N/A - At
+ Flooding ) Analysis IPEEE Power Only Approach Screening
Treatment of Seismic Risk 13 SNC submitted a Seismic Bounding Analysis Approach to NRC in September 2011 (ML112710169).
ML112710169 categorizes seismic risk into two types of contributions Seismic risk within design basis Seismic risk beyond design basis ML112710169 discusses a Generic approach, and VEGP -specific application for treating the impact of both contributions of seismic risk in RICT calculations
Treatment of Seismic Risk - Within Design Basis 14 Significance of VEGP Seismic risk within design basis Total unrecovered LOSP frequency = 3.3E-02 x 6.5E-02 = 2.1 E-03/yr Total Seismic LOSP frequency (RASP Handbook hazard data) = 9.5 E-05/yr Seismically-induced LOSP < 5% contributor The unrecovered seismically-induced loss of offsite power frequency is a small fraction of the total unrecovered LOSP frequency As a result, within design basis seismic hazard does not significantly impact RICT for removing equipment from service (e.g. diesel generator) and is bounded by the internal events CDF
Treatment of Seismic Risk - Beyond Design Basis 15 Significance of VEGP Seismic risk beyond design basis:
Seismic-induced failures of equipment are assumed to show a high degree of correlation (i.e. if one SSC fails, all similar SSCs will also fail)
Seismic CDF (SCDF) is assumed to depend on the likelihood of a single seismic-induced failure leading to core damage (i.e. single limiting plant fragility convoluted with the seismic hazard).
Therefore, removing equipment from service (RICT calculations) has little impact on SCDF However, to address any potential non-conservatism resulting from the above, the approach estimated seismic risk contribution by a bounding SCDF factor applied to the RICT Calculation
Treatment of Seismic Risk -
Basis for Bounding SCDF factor 16 Staff Report, Implications of Updated Probabilistic Seismic Hazard Estimates in Central and Eastern United States on Existing Plants, Safety/Risk Assessment, ML100270639, August 2010 has three screening values for VEGP Using 1989 EPRI: 2.6E-06 Using 1994 LLNL: 2E-05 Using 2008 USGS: 7.1E-06 Using these surrogate analyses, NRC estimated a bounding total SCDF of 2E-05/yr for VEGP which is the bounding SCDF factor applied to the RICT Calculation
Summary and Action Item Review 17 SNC appreciates the opportunity to work with the NRC on this important RI application pilot project SNC and NRC gained valuable insights on technical issues impacting 4b LAR SNC communicated its commitment for implementing 4b fleet-wide Improved safety Reduced forced outage rate Enhanced on-line and outage work planning Improved flexibility and regulatory predictability Action item review