ML19066A292
| ML19066A292 | |
| Person / Time | |
|---|---|
| Issue date: | 03/07/2019 |
| From: | Cj Fong NRC/NRR/DRA/APOB |
| To: | Mike Franovich NRC/NRR/DRA |
| References | |
| Download: ML19066A292 (3) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 March 7, 2019 MEMORANDUM TO: Michael X. Franovich, Director Division of Risk Assessment Office of Nuclear Reactor Regulation FROM: Christopher J Fong, Chief /RA/
PRA Oversight Branch (APOB)
Division of Risk Assessment Office of Nuclear Reactor Regulation
SUBJECT:
PATH FORWARD REGARDING COMMON CAUSE FAILURE FOR THE SIGNIFICANCE DETERMINATION PROCESS The purpose of this memorandum is to document the path forward regarding the development and implementation of additional common cause failure (CCF) guidance for the Significance Determination Process (SDP).
In January 2018, the Nuclear Energy Institute provided the U.S. Nuclear Regulatory Commission (NRC) with revision 1 of a White Paper for Addressing Common Cause Failure Impact within the Significance Determination Process (Agencywide Documents Access and Management System Accession No. ML18016A125), which suggested a methodology allowing qualitative assessment of CCF for the SDP.
Specifically, the paper called for detailed risk evaluations (DREs) to include: (1) sensitivity studies to compare baseline or nominal CCF calculation and the conditional CCF calculation to illustrate CCF impact, and (2) application of an adjustment factor (less than or equal to 1.0) to reduce the conditional CCF based on the purported strength of CCF defense strategies1 used by individual licensees.
NRC staff in headquarters and the regional offices provided PRA Oversight Branch (APOB) with the following comments about the paper:
- Current CCF quantitative assessment and its bases are well-documented and supported by empirical data.
CONTACT: Christopher J. Fong, NRR/DRA 301-415-8474 1
Examples of defense strategies cited in the white paper included but were not limited to design control, use of qualified equipment, testing and preventative maintenance programs, personnel training, quality control, and diversity.
M. Franovich
- Defenses against CCF are already a standard licensee practice and their effectiveness is empirically reflected in the current data collection. Additional credit for CCF defense strategies should only be considered for cases that go beyond traditional practices (and these would be difficult to define).
- The NRCs current CCF approach makes some simplifications (e.g., omission of inter-system dependencies) that should also be addressed.
APOB engaged external stakeholders during the September 2018 Reactor Oversight Process Monthly Public Meeting. APOB also conducted a standalone Category 2 public meeting on December 12, 2018 to share internal stakeholder comments and to solicit feedback from external stakeholders.
Informed by the insights gained from these interactions, APOB proposes a three-pronged approach to address internal and external stakeholders comments about the impact of CCF on the SDP. Subject to your approval, I recommend that the following approach be used on a trial-basis for one calendar year, beginning on April 1, 2019:
- i. When conducting DREs, risk analysts and senior reactor analysts will perform sensitivity studies to evaluate the impact of CCF. This is already a common practice and is consistent with RASP guidance2.
ii. Consistent with RASP CCF Ground Rule #3, licensees can provide specific information on whether plant-specific unique CCF defense strategies warrant the adjustment of the conditional CCF values. However, the burden will be on the licensees to demonstrate that their defense strategies go above and beyond what is already reflected in the current data and therefore warrant additional credit.
A common misconception in the application of this ground rule is that success of the other components in the common cause component group (CCCG) demonstrates a unique successful defensive strategy. However - as discussed in NUREG-2225 - the lack of observed degradation on the other components in the CCCG is not - by itself - indicative of a unique CCF defense strategy in probabilistic analysis.
iii. Using an existing User Need Request, the Office of Nuclear Reactor Regulation will ask RES to examine the quantitative aspect of causal alpha factors, which would categorize the effects of CCF based on the cause of the failure. To the extent practicable, APOB intends to share the results of this study with industry and other stakeholders.
APOB will perform these activities in parallel to gain efficiency. After the trial period ends, APOB - with support from the Office of Nuclear Regulatory Research (RES) and the Regional Offices - will examine the insights gained and will evaluate whether more durable changes to NRC guidance (e.g., RASP Manual) are appropriate.
2 Appendix A to Volume 1 of the RASP Handbook identifies sensitivity studies as one way to address known areas of uncertainties such as CCF modeling and human reliability analysis modeling
M. Franovich
SUBJECT:
PATH FORWARD REGARDING COMMON CAUSE FAILURE FOR THE SIGNIFICANCE DETERMINATION PROCESS DATED:
DISTRIBUTION:
RidsNrrDra RidsNrrDraAphb Nrr_Dra_Aphb MFranovich, NRR RLorson, RI JMunday, RII PLouden, RIII AVegel, RIV MThaggard, RES JNakoski, RES AZoulis, NRR RFelts, NRR MCheok, RES FArner, RI CCahill, RI CFong, NRR JYerokun, RI MFranke, RII GMacdonald, RII SFreeman, RII LKozak, RIII JHanna, RIII JLara RIII MHay, RIV RDeese, RIV DLoveless, RIV CNg, NRR JHanna, RIII ADAMS Accession No: ML19066A292 NRR-106 OFFICE NRR/DRA/APOB NRR/DRA/APOB NRR/DRA: D NAME CNg CFong MFranovich DATE 3/ /2019 3/ /2019 3/ /2019 OFFICIAL AGENCY RECORD