LIC-13-0158, Probabilistic Risk Assessment (PRA) RAI Responses 19.01, 24, and 26 - NFPA-805 Transition
| ML13309A634 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 11/04/2013 |
| From: | Cortopassi L Omaha Public Power District |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LIC-13-0158, TAC ME7244 | |
| Download: ML13309A634 (15) | |
Text
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nlllln Omaha PUblic Power District 444 South 16h Street Mall Omaha, NE 68102-2247 LlC-13-0158 November 4,2013 u.s. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Fort Calhoun Station, Unit No.1 Renewed Facility Operating License No. DPR-40 NRC Docket No. 50-285
References:
See Reference List on Page 3
SUBJECT:
Probabilistic Risk Assessment (PRA) RAI Responses 19.01, 24, and 26 - NFPA-805 Transition (ME7244)
The Omaha Public Power District's (OPPD's) response to the Nuclear Regulatory Commission's (NRC's) request for additional information (RAI) regarding the probabilistic risk assessment (PRA) is provided in the attachment to this letter. As noted in the Reference 11 email.this RAI is from the second set of the third round of RAls regarding the license amendment request (LAR) to adopt National Fire Protection Association (NFPA) 805 at the Fort Calhoun Station (FCS).
In the Reference 1 LAR, OPPD requested an amendment to Renewed Facility Operating License No. DPR-40 for FCS, Unit No.1, to adopt NFPA 805, Performance-Based Standard for Fire Protection for Light Water Reactor Generating Plants (2001 Edition). The NRC staff reviewed OPPD's application and determined that additional information was required in order to complete their review and subsequently transmitted RAls via References 2, 6 and 9. OPPD provided responses to these RAls in References 3, 4, 5,7, 8, and 10. The NRC indicated that the staff had reviewed the information provided by the licensee [in References 3, 4, 5, 7, 8, and 10] and determined that additional information specified in the Reference 11 email is needed for the staff to complete its review.
As requested by Reference 11, the attachment to this submittal contains responses to PRA RAls 19.01, 24, and 26, which were to be provided by November 6, 2013. Please note that responses to PRA RAls 07.02 and 25, which were also due November 6,2013, were provided in Reference
- 12.
There are no new regulatory commitments being made in this letter because of the enclosed NFPA 805 RAI responses. Please note, as indicated in References 3, 4, 5, 7, 8, 10, and 12, OPPD plans to supplement the NFPA 805 transition LAR, which will reflect the applicable information delineated in the enclosed RAI responses.
AR 48249 is tracking the LAR supplement.
Employment with Equal Opportunity
U. S. Nuclear Regulatory Commission LlC-13-0158 Page 2 In accordance with 10 CFR 50.91, a copy of this letter, without the attachment, is being provided to the designated State of Nebraska official.
If you should have any questions regarding this submittal or require additional information, please contact Mr. Bill R. Hansher, Supervisor-Nuclear Licensing, at 402-533-6894.
I declare under penalty of perjury that the foregoing is true and correct.
Executed on November4,2013. ~
Louis P. Cortopassi Site Vice President and CND LPC/BJV Imle
Attachment:
Response to PRA RAls 19.01, 24, and 26 c:
M. L. Dapas, NRC Regional Administrator, Region IV J. W. Sebrosky, NRC Senior Project Manager L. E. Wilkins, NRC Project Manager J. C. Kirkland, NRC Senior Resident Inspector Manager Radiation Control Program, Nebraska Health & Human Services, R & L Public Health Assurance, State of Nebraska (w/out attachments)
U. S. Nuclear Regulatory Commission LlC-13-0158 Page 3 Reference List
- 1. Letter from OPPD (J. A. Reinhart) to NRC (Document Control Desk), License Amendment Request 10-07, Proposed Changes to Adopt NFPA 80S, Performance-Based Standard for Fire Protection for Light Water Reactor Generating Plants (2001 Edition) at Fort Calhoun Station, dated September 28, 2011 (LlC-11-0099) (ML112760660)
- 2. Letter from the NRC (L. E. Wilkins) to OPPD (David J. Bannister), Fort Calhoun Station, Unit No.1 - Request for Additional Information Re: License Amendment Request to Adopt National Fire Protection Agency Standard NFPA 805 (TAC No. ME7244), dated April 26, 2012 (NRC-12-0041) (ML121040048)
- 3. Letter from OPPD (D. J. Bannister) to NRC (Document Control Desk), Responses to Requests for Additional Information Re: License Amendment Request 10-07 to Adopt NFPA 80S, "Performance-Based Standard for Fire Protection for Light Water Reactor Generating Plants," 2001 Edition, at Fort Calhoun Station, dated July 24, 2012 (LlC-12-0083)
- 4. Letter from OPPD (D. J. Bannister) to NRC (Document Control Desk), Responses to Requests for Additional Information Re: License Amendment Request 10-07 to Adopt NFPA 80S, "Performance-Based Standard for Fire Protection for Light Water Reactor Generating Plants," 2001 Edition, at Fort Calhoun Station, dated August 24, 2012 (LlC-12-0120)
(ML12240A151 )
- 5. Letter from OPPD (L. P. Cortopassi) to NRC (Document Control Desk), Responses to Requests for Additional Information Re: License Amendment Request 10-07 to Adopt NFPA 80S, "Performance-Based Standard for Fire Protection for Light Water Reactor Generating Plants," 2001 Edition, at Fort Calhoun Station, September 27, 2012 (LlC-12-0135)
- 6. Email from NRC (L. E. Wilkins) to OPPD (D. L. Lippy), DRAFT: Fort Calhoun NFPA 805, Second Round (ME7244), dated February 22,2013 (NRC-13-0014)
- 7. Letter from OPPD (M. J. Prospero) to NRC (Document Control Desk), Responses to Second Request for Additional Information Re: License Amendment Request to Adopt NFPA 805 at Fort Calhoun Station (TAC No. ME7244), dated April 23, 2013 (LlC-13-0033)
- 8. Letter from OPPD (L. P. Cortopassi) to NRC (Document Control Desk), Remaining Responses to Second Request for Additional Information Re: License Amendment Request to Adopt NFPA 805 at Fort Calhoun Station (TAC No. ME7244), dated May 21,2013 (LlC 0060)
- 9. Email fromNRC(J.M.Sebrosky)toOPPD(D.L.Lippy).FortCalhounNFPA805.Third Round of RAls (ME7244), dated June 27,2013 (NRC-13-0081)
- 10. Letter from OPPD (L. P. Cortopassi) to NRC (Document Control Desk), Responses to Third Request for Additional Information Regarding License Amendment Request to Adopt NFPA 805 at Fort Calhoun Station (TAC No. ME7244), dated July 29,2013 (LlC-13-0096)
- 11. Email fromNRC(L.E.Wilkins)toOPPD(D.L.Lippy).FortCalhounNFPA805.Third Round, Second Part, of RAls (ME7244), dated August 14, 2013 (NRC-13-0102)
- 12. Letter from OPPD (L. P. Cortopassi) to NRC (Document Control Desk), Probabilistic Risk Assessment (PRA) RAI Response - NFPA-805 Transition (ME7244), dated October 11, 2013 (LlC-13-0142)
LI C-13-0 158 Attachment Page 1 Omaha Public Power District (OPPD)
Response to PRA RAls 19.01, 24, and 26 License Amendment Request to Adopt National Fire Protection Association Standard 805 Performance-Based Standard for Fire Protection for Light Water Reactor Generating Plants at Fort Calhoun Station, Unit 1 (TAC No. ME7244)
By letter dated September 28, 2011 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML112760660), as supplemented by letters dated December 19 and 22, 2011, and March 20, 2012 (ADAMS Accession Nos. MLl13540334, MLl1363A077, and ML12083A147, respectively), Omaha Public Power District, (the Licensee), submitted a license amendment request (LAR) to transition their fire protection licensing basis at the Fort Calhoun Station, Unit 1, from Title 10 of the Code of Federal Regulations (CFR), Section 50.48(b), to 10CFR50.48(c), National Fire Protection Association Standard NFPA 805 (NFPA 805). A review team, consisting of U.S. Nuclear Regulatory Commission (NRC) staff and contractors from Pacific Northwest National Laboratory (PNNL) and the Center for Nuclear Waste Regulatory Analyses (CNWRA) participated in a regulatory audit of Fort Calhoun in Blair, NE from March 5
-9,2012. By letter dated April 26, 2012, (ADAMS Accession No. ML12198A406) the NRC issued requests for additional information (RAls). By letters dated July 24, 2012 (ADAMS Accession No. ML12208A131), August 24,2012 (ADAMS Accession No. ML12240A151), and September 27,2012 (ADAMS Accession No. ML12276A046) the licensee provided responses to the RAls.
The NRC staff reviewed the information provided by the licensee in response to the first set of RAls and determined that additional information was needed for the staff to complete its evaluation. Consequently, the staff issued a second round of RAls on February 22, 2013, (ADAMS Accession No. ML13053A226) and a third round of RAls on June 27, 2013 (ADAMS Accession No. ML13178A035). The licensee responded to these RAls in letters dated April 23, 2013 (ADAMS Accession No. ML13116A015), May 21, 2013 (ADAMS Accession No. ML13144A814), and July 29,2013 (ADAMS Accession No. ML13211A055).
The U.S. NRC staff has reviewed the information provided in your application and determined that additional information is required in order to complete its review. These RAls can be found below. The NRC considers these RAls to be the second set of the third round of RAls.
Based on discussions with you on August 13, 2013, it was agreed that a response to the RAls found below will be provided in accordance with the following schedule:
Safe Shutdown Analysis (SSA) RAI response to be provided by September 13, 2013 PRA RAls 01.i.02, 01.j.02, 01.j.03, 23.01, and 27 responses to be provided by October 7, 2013 PRA RAls 07.02,19.01,24,25, and 26 responses to be provided by November 6,2013.
In addition, as discussed with you during the August 13, 2013, phone call the staff has determined that you no longer need to provide a response to SSA RAI 07.01 that was issued to you on June 27, 2013 (ADAMS Accession No. ML13178A035). The staff determined that SSA RAI 07.01 response is not needed in order for the staff to complete its safety evaluation. The staff also discussed with you during the August 13, 2013, phone call that the response to PRA RAI 24 should include two additional sensitivity studies as a result of issues that were raised during a July 22 through July 24, inspection at your site.
LlC-13-0158 Attachment Page 2 Should the NRC determine that the RAls found below are no longer necessary prior to the dates found above, the request will be withdrawn. If circumstances result in the need to revise the requested response date, please contact me or Joe Sebrosky.
LlC-13-0158 Attachment Page 3 E.1 PRA RAI 19.01 Appendix E: PRA RAI 19.01 By letter dated April 23, 2013 (ADAMS Accession No. ML13116A015) the licensee responded to PRA RAI 19 and stated that high concentrations of conduits were considered when identifying pinch points. However, the highest concentration of cables is not necessarily correlated with the locations with high CCDP which may have fewer cables. Please describe the criteria used to identify high concentrations of conduits and justify how implementation of this criteria ensures that pinch points are identified.
OPPD Response to PRA RA119.01 The FCS fire PRA postulates transient fires in areas where the highest concentrations of cable trays exist within a given compartment, and where the 98th percentile heat release rate of a potential transient fire could damage those cable trays. High concentrations of conduits are also considered in this process.
However, as identified by this RAI, an area with the highest concentration of cables may not necessarily be the area with the highest CCDP or CLERP. For example, failing a high concentration of cables related to the auxiliary boiler might have a lower CCDP than failing a couple cables related to a pressurizer PORV.
To assess the implemented process' effectiveness in postulating transient fires at the most conservative locations (i.e., "pinch points"), each transient fire scenario was replaced with a collection of scenarios using a gridded approach, covering the entire floor area of its associated compartment.
The transient fire frequency for the compartment was apportioned to each individual scenario based on the fraction of total compartment floor area that each scenario occupies. With this approach, all potential transient fire locations within a given compartment are considered.
The following table summarizes the transient fire contribution to total plant CDF, total plant LERF, VFDR ~CDF, and VFDR ~LERF for the fire PRA used in response to PRA RAI 07.a (individual scenarios postulated at pinch points) and for the sensitivity study (gridded approach covering entire compartment). The fire PRA model supporting response to PRA RAI 07.a is used here as the base case, since it eliminated Un-reviewed Analysis Methods (UAMs), some of which affect transient fire scenario development.
LI C-13-0 15B Attachment Page 4 Transient Fire Contribution to Total VFDR ACDF for NFPA 805 Transition (/yr)
Transient Fire Contribution to Total VFDR ALERF for NFPA 805 Transition (/yr)
Transient Fire Contribution to Total CDF (internal, flood, fire) (/yr)
Transient Fire Contribution to Total LERF (internal, flood, fire) (/yr)
Base Case Sensitivity Case (Pinch Point Approach)
(Gridded Approach) 6.B5E-07 3.40E-07 5.95E-OB B.13E-09 3.60E-06 1.BBE-06 1.60E-07 1.0BE-07 The gridded approach reduced the transient fire contribution to each of the NFPA B05 risk metrics as compared to the pinch point approach implemented by the base fire PRA. This behavior is generally caused by the base fire PRA, for a given compartment, conservatively applying the entire transient fire frequency to the location with the highest concentration of cables. On the other hand, the more realistic and comprehensive gridded approach apportions the compartment frequency across all possible transient fire locations within the compartment, even those with lower concentrations of cables.
The results of this sensitivity study provide confidence that the base fire PRA transient fire development process is overall conservative in the context of the NFPA B05 risk metrics.
E.3 Supporting Information for PRA RAI 19.01 Supporting information documented in Westinghouse Proprietary Class 2 L TR-RAM-II-13-053 Revision 1.
LlC-13-0158 Attachment Page 5 G.1 PRA RAI 24 Appendix G: PRA RAI 24 Section 2.4.3.3 of NFPA 80S states that the probabilistic safety assessment (PSA) (PSA is also referred to as PRA) approach, methods, and data shall be acceptable to the authority having jurisdiction (AHJ). Section 2.4.4.1 of NFPA-80S states that the change in public health risk from any plant change shall be acceptable to the AHJ. Regulatory Guide (RG) 1.174, "An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis," provides quantitative guidelines on CDF and LERF, and identifies acceptable changes to these frequencies that result from proposed changes to the plants licensing basis and describes a general framework for determine the acceptability of risk-informed changes.
The responses to the following RAls provided sensitivity analyses to show the impact on fire risk of the indicated PRA modeling, and this included PRA upgrades to meet Capability Category II (CC-II) requirements:
LAR Section 4.S.1.2 regarding the use of four methods that are deviations from the guidance in NUREGlCR-68S0 and NRC-approved frequently asked questions (FAQs),
with a composite sensitivity analysis of these four methods provided in Section W.2 of the LAR.
The four methods are 1) generic severity factor/non-suppression probability for electrical cabinets, 2) pump fire frequency apportioning, 3} diesel generator generic severity factor/non-suppression probability, and 4} application of a draft version of FAQ 08-00S0, "Manual Non-Suppression Probability," (ADAMS Accession No. ML092190SSS, closure memo).
PRA RAI 01.e.01 regarding unavailability of the Halon system.
PRA RAI 01.h.i, ii, and iii regarding manual suppression for multi-compartment analysis (MCA) with integration of MCA into the risk estimates.
PRA RAI 01.h.01 regarding inappropriate crediting of gaseous suppression systems in the MCA.
PRA RAI 01.h.02 regarding time available for manual fire suppression for non-rated fire barriers in the MCA.
PRA RAI 01.i.02 regarding credit for MCR abandonment on loss of control PRA RAI 01.j.01 regarding both MCR abandonment, CCDP and main control board (MCB) fire spread that threatens MCR abandonment.
The sensitivity analysis provided in response to RAI 01.j.01 encompassed both of these issues. If the MCR abandonment CCDP is revised in response to RAI 01.j.02, the revised CCDP should be used in response to this RAI.
LlC-13-0158 Attachment Page 6 PRA RAI 01.j.03 regarding use of optical density criterion for abandonment. If the MCR abandonment probability is revised in response to RAI 01.j.03, the revised probability should be used in response to this RAI.
PRA RAI 07.a and b regarding credit for hot work procedural compliance and continuous fire watch of stored combustible material.
PRA RAI 07.02 regarding treatment of transient fires in the CSR (FC41).
If the treatment of transient fires in FC41 is revised in the response to RAI 07.02, the revised treatment should be used in response to this RAI.
PRA RAI 08 regarding credit for Control Power Transformers (CPTs).
PRA RAI lS.c regarding component boundary definitions.
PRA RAI lS.d regarding state-of knowledge correlations (SOKC) including consideration of correlated fire related factors.
PRA RAI 27 on update of fire frequencies with potentially challenging event data.
FM RAI 01.a regarding wall and corner effects.
FM RAI 01.b regarding non-cable intervening combustibles.
FM RAI 01.d.iii regarding use of Beyler's correlation in closed compartments.
FM RAI OS.c.i regarding soot yield.
- a. Consistent with the requirement that the change in risk is developed using acceptable methods and meets the acceptance guidelines, provide the results of a composite sensitivity analysis that shows the integrated impact on the fire risk (CDF, LERF, ~CDF,
~LERF). The composite sensitivity analysis should utilize the accepted method that was substituted for the proposed method in all the above studies. In this composite analysis, for those cases where the individual issues have a synergistic impact on the results, a simultaneous analysis must be performed.
For those cases where no synergy exists, a one at a time analysis may be done.
In addition, an additional composite sensitivity analysis that includes only the sensitivity analyses believed appropriate may be provided.
- b. If the acceptance guidelines are exceeded, please provide justification of how RG 1.174 is nevertheless satisfied and, if applicable, a description of any new modifications or operator actions being credited to reduce /). risk and the associated impacts to the fire protection program (FPP).
Self-approval based on the results of the PRA after transition also requires the use of acceptable methods.
For each of the above methods, identify which method is
LI C-13-0 158 Attachment Page 7 intended to be used in the PRA that will be used to support post-transition change in risk evaluations. Continued use of unacceptable methods will prohibit the staff from completing its review for self approval.
OPPD Response to PRA RAI 24 Part 'a' The base fire PRA supporting LlC-11-0099 was revised to replace the "proposed methods" with "accepted methods" associated with each of the sensitivity studies identified by this RAI, as described in the following table.
Sensitivity Study Treatment LAR Section 4.5.1.2 The electrical cabinet generic severity factor / non-suppression probability was eliminated. All electrical cabinet severity factors and non-suppression probabilities were either set to 1.0 or replaced with calculated values using NUREG/CR-6850 and its Supplement 1.
The pump frequency apportioning based on run-time was replaced with apportioning based on pump count in accordance with NUREG/CR-6850.
Credit to the diesel generator generic severity factor / non-suppression probability was eliminated.
Use of the draft version of FAQ 08-0050, "Manual Non-Suppression Probability," was replaced with use of the final version documented in NUREG/CR-6850 Supplement 1.
PRA 01.e.01 Credit to the Halon systems was revised to included unavailability in accordance with response to PRA 01.e.01.
PRA 01.h.i, ii, iii Credit to manual suppression within the mUlti-compartment analysis was revised to be consistent with response to PRA 01.h.i, ii, and iii.
The risk metrics resulting from this composite sensitivity study include the contribution of the multi-compartment analysis.
PRA 01.h.01 Credit to gaseous suppression within the multi-compartment analysis was eliminated.
PRA 01.h.02 The time available for manual suppression within the multi-compartment analysis was revised to be consistent with response to PRA 01.h.02.
PRA 01.i.02 Credit to the alternate shutdown process upon control room abandonment due to loss of control was eliminated.
PRA 01.j.01 Replaced the base fire PRA CCDP and CLERP associated with alternate shutdown (0.1 and 0.01, respectively) with the values calculated in response to PRA 01.j.01, which were developed based on human reliability analysis and consideration of equipment reliability. Note that this analysis did not require revision as a result of PRA 01.j.02.
Included contribution of control room abandonment due to main control board fires consistent with response to PRA 01.j.01.
LlC-13-0158 Attachment Page 8 Sensitivity Study PRA 01.j.03 PRA 07.a, b PRA07.02 PRA08 PRA 15.c PRA 15.d PRA27 FM 01.a FM 01.b FM 01.d.iii FM 05.c.i 480 VAC Crosstie 125 VDC Crosstie Treatment Implemented the optical density abandonment criterion (3.0 m-1) used in response to PRA 01.j.03. Note that this analysis did not require revision as a result of PRA 01.j.03.
Eliminated credit to the hot work procedural compliance factor, and revised credit to continuous fire watch of stored combustible material, in accordance with response to PRA 07.a and 07.b.
Treatment of FC41 transient fires did not require revision as a result of PRA 07.02 Conservatively removed all credit to conditional wire-to-wire short probabilities in accordance with response to PRA 08.
Incorporated component boundary definitions in accordance with response to PRA 15.c.
Addressed the state-of-knowledge correlation in accordance with response to PRA 15.d.
Incorporated Bayesian updated fire frequencies in accordance with response to PRA 27.
Addressed wall and corner effects in accordance with response to FM 01.a.
Incorporated treatment of non-cable intervening combustibles in accordance with response to FM 01.b.
Addressed modeling of closed compartments in accordance with response to FM 01.d.iii.
Implemented soot yields that conservatively bounded the values used in response to FM OS.c.i.
Per NRC request, included in this composite sensitivity study the potential for 480 VAC and 125 VDC crosstie breaker random failure to trip on over-current.
FCS initially exceeded the R.G. 1.174 Revision 1 numerical acceptance guidelines when all of the above items were aggregated into a single composite sensitivity study. To restore margin against the numerical acceptance guidelines, the following fire PRA model refinements were implemented:
incorporation of revised station battery depletion times, elimination of erroneous failure mapping for three switchgear room fire scenarios, elimination of double-counting issues, and crediting suppression (in accordance with NUREG/CR-6850 Supplement 1) for fire scenarios in which suppression was originally not credited. All of the refinements were within the guidance of NUREG/CR-6850 and its Supplement 1.
Note that the erroneous mapping was identified in 2010 and was a result of a drawing inaccuracy.
CR2010-3418 was initiated to correct the drawing.
The following table summarizes the total plant CDF, total plant LERF, VFDR f1CDF, and VFDR f1LERF for the base fire PRA (Reference LlC-11-0099) and for the composite sensitivity study.
LlC-13-01S8 Attachment Page 9 Net VFDR ~CDF for NFPA 805 Transition (/yr)
Net VFDR ~LERF for NFPA 805 Transition (/yr)
Total CDF (internal, flood, fire) (/yr)
Total LERF (internal, flood, fire) (/yr)
Base Fire PRA Composite (LlC-11-0099)
Sensitivity Study S.72E-06 6.02E-06 6.67E-07 8.10E-07 6.01 E-OS 9.99E-OS 4.82E-06 8.S3E-06 In conclusion, the total CDF, total LERF, VFDR boCDF, and VFDR boLERF remain within RG 1.174, Revision 1, Region " when the base fire PRA supporting LlC-11-0099 is revised to replace the "proposed methods" with "accepted methods" associated with each of the sensitivity studies identified by this RAI.
While the total plant CDF and LERF acceptance guidelines (1.00E-04 /yr and 1.00E-OS /yr, respectively) are met with little margin, various conservatisms remain in the fire PRA supporting this composite sensitivity study.
Several of the individual sensitivity studies were intentionally very conservative for the purpose of demonstrating margin against the particular issue in question. For example, PRA 08 questions the credit afforded by control power transformers when calculating conditional wire-to-wire short probabilities. The sensitivity study in response to PRA 08 conservatively removed all credit to conditional wire-to-wire short probabilities from the FPRA, as opposed to applying a reduced credit only for those circuits involving control power transformers. As another example, the sensitivity study response to PRA 01.j.01 conservatively assumed that any fire spread within the main control board would be sufficient to cause abandonment, as opposed to performing fire modeling to assess the extent of fire spread required to threaten habitability.
In addition to conservatisms within the sensitivity studies, various conservatisms also remain within the base fire PRA.
This conservative composite sensitivity study, in addition to conservatisms remaining within the base fire PRA, provide confidence that the Fort Calhoun Station is well within RG 1.174, Revision 1, Region
" for the NFPA 80S transition.
Part Ib' The RG 1.174, Revision 1, Region " numerical acceptance guidelines were not exceeded as a result of this sensitivity study. The total CDF, total LERF, VFDR boCDF, and VFDR boLERF remain within RG 1.174, Revision 1, Region II when the base fire PRA supporting LlC-11-0099 is revised to replace the "proposed methods" with "accepted methods" associated with each of the sensitivity studies identified by this RAI.
LlC-13-0158 Attachment Page 10 Part 'c' The post-transition FCS NFPA 805 program will initially use the fire PRA supporting this composite sensitivity study, which replaces the "proposed methods" with "accepted methods" associated with each of the sensitivity studies identified by this RAI.
Treatment of these methods may be revised or superseded by analysis within the guidance of NUREG/CR-6850 or other reports documenting methods acceptable to the NRC for the purpose of NFPA 805. As an example, where the sensitivity study conservatively assumed that a scenario involving non-cable intervening combustibles would cause a damaging hot gas layer, OPPD may choose to replace that conservative assumption with fire modeling using the guidance of NUREG/CR-6850. The intent is that the FCS NFPA 805 fire PRA will use methods acceptable to the NRC, and this RAI response is not intended to limit or prevent future revision to the fire PRA using methods acceptable to the NRC.
G.3 Supporting Information for PRA RAI 24 Supporting information documented in Westinghouse Proprietary Class 2 L TR-RAM-II-13-053 Revision 1.
LlC-13-0158 Attachment Page 11 1.1 PRA RAI 26 Appendix I: PRA RAI 26 Section 2.4.3.3 of NFPA 805 states that the PSA (PSA is also referred to as PRA) approach, methods, and data shall be acceptable to the AHJ. Section 2.4.4.1 of NFPA-805 states that the change in public health risk from any plant change shall be acceptable to the AHJ. RG 1.174, provides quantitative guidelines on CDF and LERF, and identifies acceptable changes to these frequencies that result from proposed changes to the plants licensing basis and describes a general framework for determine the acceptability of risk-informed changes.
With regard to the responses to PRA RAI 01.i (July 24, 2012, ADAMS Accession No. ML12208A131) and PRA RAI 01.i.01.a (April 23, 2013, ADAMS Accession No. ML13116A015),
regarding use of fire ignition frequencies from NUREG/CR-6850, Supplement 1, indicate if the acceptance guidelines of RG 1.174 may be exceeded when this sensitivity study is applied to the integrated sensitivity study of PRA RAI 24 (above). If these guidelines may be exceeded, provide a description of fire protection, or related, measures that can be taken to provide additional DID, as directed in the resolution of FAQ 08-0048, "Revised Fire Ignition Frequencies," (ADAMS Accession No. ML092190457, closure memo).
OPPD Response to PRA RAI 26 NUREG/CR-6850 Supplement 1 requires a sensitivity study be performed for ignition source bins characterized by an alpha value less than or equal to 1.0, indicative of relatively large uncertainty in the fire frequency due to sparsity of data. This includes Bins 1, 4, 9, 11, 13, 15.1, 22, and 31.
Bins 1, 4, 13, and 15.1 are relevant to this RAI response.
Regarding Bin 9, NUREG/CR-6850 Supplement 1 states that a sensitivity study need not be performed for Bin 9, as the reported alpha value appears to be in error. Regarding Bins 11 and 31, the composite sensitivity study performed for PRA 24 used the frequencies superseding NUREG/CR-6850 Supplement 1 and endorsed by the NRC via ML12172A406. Regarding Bin 22, FCS does not have reactor protection system motor generator sets.
The RG 1.174, Revision 1, Region II numerical acceptance guidelines are exceeded when the NUREG/CR-6850 frequencies for Bins 1, 4, 13, and 15.1 are used in place of the more current NUREG/CR-6850 Supplement 1 values.
The Bin 1 station batteries are not fire risk significant in the sense that they are neither within the top 95% of total fire CDF or LERF nor do they individually contribute greater than 1% of CDF or LERF.
While the Bin 13 dryers are relatively low contributors to total CDF and LERF (approximately 0.32%
and 0.24%, respectively), they are "significanf' in the sense that they are within the top 95% of total fire CDF and LERF (93% and 94%, respectively). However, this is largely due to their conservative modeling as failing all targets within their respective compartment.
LlC-13-0158 Attachment Page 12 The Bin 4 Main Control Board (MCB) is a dominant contributor to overall fire risk. The FCS MCB includes a major defense-in-depth element that is not credited by the fire PRA. Specifically, using the alternate shutdown process to recover from abandonment upon loss of control is not credited, primarily because a method acceptable to the NRC has not yet been developed.
Nonetheless, recovery using the alternate shutdown process for severe MCB fires is proceduralized and periodically trained upon at FCS. It is anticipated that once an acceptable method is developed, the calculated risk decrease will offset the calculated increase caused by using the NUREG/CR-6850 Bin 4 frequency, which is about a factor of three higher than the more current Supplement 1 value.
Bin 15 Electrical Cabinets are also dominant contributors to overall fire risk. While electrical cabinets are installed throughout the plant, their fire risk contribution is particularly concentrated in the switchgear rooms (FC36A and FC36B), MCC area (FC34C), and electrical penetration area (FC34B-1).
The higher risk fire scenarios in these areas broadly impact the safety-related electrical distribution system, and along with random failures can lead to station blackout. As an additional defense-in-depth measure to compensate for uncertainty in the Bin 15.1 fire frequency, OPPD plans to station a breathing apparatus, flashlight, relevant procedure(s), and tools in the vicinity of these areas.
This defense-in-depth measure will increase the reliability of station blackout mitigating actions, including the minimization of DC loads, obtaining steam generator water level measurement outside the control room, and operating an auxiliary feedwater pump.
OPPD may also pursue crediting an alternate steam generator level monitoring system, such as the distributed control system (DCS), or remote indication independent of the fire-affected area, which provides a redundant source of steam generator level indication. Credit will require verification that this system is electrically independent of the areas for which it is credited and may require procedural enhancements to notify operators of its availability during fire events. If credit for this system is viable to mitigate significant fire sequences involving station blackout, then this credit may be implemented in addition to, or in lieu of, stationing the breathing apparatus and other equipment as described above. If credit for this system is not viable, then OPPD will station the breathing apparatus and other equipment as described above.