ML17258A638
| ML17258A638 | |
| Person / Time | |
|---|---|
| Issue date: | 09/25/2017 |
| From: | Casto G Office of Nuclear Reactor Regulation |
| To: | |
| Robinson J | |
| Shared Package | |
| ML17258A687 | List: |
| References | |
| NUREG/CR-6850 | |
| Download: ML17258A638 (3) | |
Text
September 25, 2017 MEMORANDUM TO: APLB Files FROM: Greg A. Casto, Chief /RA/
PRA Licensing Branch B Division of Risk Assessment Office of Nuclear Reactor Regulation
SUBJECT:
CLOSE-OUT OF FIRE PROBABILISTIC RISK ASSESSMENT FREQUENTLY ASKED QUESTION 16-0010 ON ALTERNATIVE METHODOLOGY TO NUREG/CR-6850 FOR MAINTAINING FIRE PROBABALISTIC RISK ASSESSMENT IGNITION FREQUENCIES WEIGHTING FACTORS
Background
During industry peer reviews and Nuclear Regulatory Commission (NRC) staff review of Fire Probabilistic Risk Assessments (FPRAs) related to license amendment requests (LARs) to implement National Fire Protection Association Performance-Based Standard for Fire Protection for Light-Water Reactor Electric Generating Plants (NFPA 805, 10 CFR 50.48(c)),
methods and approaches different from the accepted methods were encountered. NRC staff, the Nuclear Energy Institute (NEI), and representatives from the nuclear industry worked to identify these methods, approaches, and factors in current LARs (including but not limited to NFPA 805 LARs), and to address them through a frequently asked question (FAQ) process.
This FAQ process is only one NRC process whereby a new FPRA method can be reviewed or developed.
NUREG/CR-6850, EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities, Final Report, includes a general method for calculating fire ignition frequencies. Essentially, the plant wide fire ignition frequency for a location as defined in Task 6 of NUREG/CR-6850 is distributed equally to all ignition sources within that location. If an ignition source in a location is added or removed, the ignition frequency for all ignition sources of the same type within that location should be recalculated.
FPRA FAQ 16-0010, Alternative Methodology to NUREG/CR-6850 for Maintaining FPRA Ignition Frequencies Weighting Factors, (enclosed), provides an alternative method to NUREG/CR-6850 for maintaining FPRA ignition source fire frequencies. This FAQ simplifies the change to the FPRA upon the addition or removal of a fire ignition source.
CONTACTS: J.S. Hyslop, NRR/DRA (301) 415-4107 Jay Robinson, NRR/DRA (301) 415-2878
G. Casto 2 September 25, 2017 Discussion and Conclusion The NRC staff and the nuclear industry held a series of public meetings to discuss the resolution of FPRA FAQ 16-0010.
The guidance in this FAQ establishes a simplified, component based fire ignition frequency from the overall plant fire ignition frequency (rather than an industry-wide component based fire ignition frequency), and eliminates the need to recount components to recalculate the NUREG/CR-6850 fire ignition frequency results for existing fire scenarios unaffected by the removal or addition of an ignition source. Instead, the calculation of fire ignition frequency due to an added or removed ignition source is simplified with this FAQ, and provides a more pragmatic approach for evaluating its addition or removal. To account for an additional fire ignition source, the additional FPRA ignition source is attributed the same fire ignition frequency as those same ignition sources existing in the appropriate location per Task 6 of NUREG/CR-6850. For a removed fire ignition source, the fire scenario is removed with no effect on the remaining fire scenarios. Cable loading is maintained for fire ignition frequency unless a specified change in cable loading occurs.
However, this FAQ does provide guidance for the licensee to reestablish their fire ignition frequencies, consistent with the actual component count and amount of cable loading when new generic fire ignition frequencies are developed and made available. This realignment is done consistent with the licensees PRA maintenance and upgrade process, as indicated in the FAQ.
The guidance in FPRA FAQ 16-0010 is acceptable for use by licensees.
Enclosure
- 1. FAQ 16-0010 Alt. Method
G. Casto 3 September 25, 2017
SUBJECT:
CLOSE-OUT OF FIRE PROBABILISTIC RISK ASSESSMENT FREQUENTLY ASKED QUESTION 16-0010 ON ALTERNATIVE METHODOLOGY TO NUREG/CR-6850 FOR MAINTAINING FIRE PROBABALISTIC RISK ASSESSMENT IGNITION FREQUENCIES WEIGHTING FACTORS DISTRIBUTION:
SRosenberg, NRR MSalley, RES RidsNrrDraAplb RidsNrrDraApla RidsNrrDra vka@nei.org ADAMS Package Accession: ML17258A687 ADAMS Memo Accession: ML17258A638 ADAMS Enclosure Accession No.: ML17258A686 OFFICE DRA/APLB DRA/APLB DRA/APLB NAME JRobinson JHyslop GCasto DATE 09 /15 /17 09 / 21 /17 09 / 25 /17 OFFICIAL RECORD COPY