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MONTHYEARML23361A1022023-12-21021 December 2023 Security Rule Exemption Request - ISFSI Docket No. Reference ML23321A1222023-11-17017 November 2023 NRR E-mail Capture - Final RAI - D.C. Cook 1 & 2 - License Amendment Request Regarding Neutron Flux Instrumentation ML23052A1502023-02-21021 February 2023 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 and 2 - Acceptance of License Amendment Request Regarding Neutron Flux Instrumentation ML22307A2532022-11-0303 November 2022 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit No. 2 - Verbal Authorization of Relief Request ISIR-5-06 Regarding Alternative to N-729-6 for RPV Head Visual Examination ML22122A0902022-04-29029 April 2022 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 and 2 - Acceptance of License Amendment Request to Revise Technical Specifications Consistent with TSTF-554, Revision 1 ML22250A6712022-02-16016 February 2022 Outline Submittal Notification Email DC-Cook 2022 ML21341A6252021-12-0707 December 2021 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 and 2 - Acceptance of License Amendment Request to Revise Technical Specifications Consistent with TSTF-577, Revision 1 ML21307A3352021-11-0303 November 2021 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 and 2 - Final RAI - License Amendment Request Regarding Containment Water Level Instrumentation ML21236A0262021-08-23023 August 2021 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit No. 2 - Acceptance of License Amendment Regarding Changes to Reactor Vessel Heatup and Cooldown Curves and Low Temperature Overpressure Protection System Requirements ML21140A3052021-05-20020 May 2021 NRR E-mail Capture - Final RAI - D.C. Cook 1 & 2 - Relief Request ISIR-4-11, Impractical Examinations for the Fourth 10-Year ISI Interval ML21113A2812021-04-23023 April 2021 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 and 2 - Acceptance of License Amendment Request Regarding Containment Water Level Instrumentation ML21089A0222021-03-24024 March 2021 DC Cook Power Operated Valves (POV) Preliminary Request for Information ML21082A0262021-03-22022 March 2021 Acceptance of Relief Request ISIR-4-11, Impractical Examinations for the Fourth 10-Year ISI Interval ML21049A2682021-02-16016 February 2021 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit No. 2 - Final RAI - License Amendment Request for One-Time Extension Containment Type a ILRT ML21026A3472021-01-26026 January 2021 NRR E-mail Capture - Final RAI - D.C. Cook 1 & 2 - Relief Request REL-PP2 for Pump and Valve IST Fifth 10-year Interval ML21008A4742021-01-0808 January 2021 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit No. 2 - Acceptance of License Amendment Request for One-Time Extension Containment Type a ILRT ML20366A1012020-12-31031 December 2020 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit No. 2 - Acceptance of License Amendment Request for One-Time Deferral of Steam Generator Inspection ML20316A0152020-11-0606 November 2020 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 and 2 - Acceptance of Relief Request REL-PP2 for Pump and Valve IST Fifth 10-year Interval ML20318A0202020-10-16016 October 2020 NRR E-mail Capture - Regarding Public Comment on D.C. Cook, Unit 1 Request for Relief from Nozzle Inspections, Code Case N-729 ML20318A0192020-10-15015 October 2020 NRR E-mail Capture - (External_Sender) Supplemental Public Comment on D.C. Cook, Unit 1 Request for Relief from Nozzle Inspections, Code Case N-729 ML20289A7122020-10-15015 October 2020 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit No. 1 - Verbal Authorization of Relief Request ISIR-5-04 Regarding Alternative to N-729-6 for RPV Head Visual Examination ML20290A4252020-10-15015 October 2020 Verbal Authorization of Relief Request ISIR-5-04 Regarding Alternative to N-729-6 for RPV Head Visual Examination ML20318A0182020-10-0909 October 2020 NRR E-mail Capture - (External_Sender) Public Comment on D.C. Cook, Unit 1 Request for Relief from Nozzle Inspections, Code Case N-729 ML20289A1192020-10-0909 October 2020 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 and 2 - Acceptance of Relief Request for Alternative to N-729-4 for RPV Head Visual Examination ML20181A4122020-06-29029 June 2020 NRR E-mail Capture - Final RAI - D.C. Cook 1 - One-Time Extension, Containment Type a ILRT Frequency ML20149K6272020-05-28028 May 2020 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 and 2 - Acceptance of License Amendment and Exemptions Regarding UFSAR 10 CFR 50.71(e)(4) Update Schedule (Epids: L-2020-LLA-0100, L-2020-LLE-0052, L-2020-LLE-0053) ML20149K4332020-05-26026 May 2020 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 and 2 - Acceptance of License Amendment Request to Revise Technical Specifications Consistent with TSTF-567, Revision 1 ML20141L8112020-05-20020 May 2020 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 and 2 - Acceptance of Relief Request Regarding Impracticality for Inservice Inspection for Certain Welds ML20141L6062020-05-20020 May 2020 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 and 2 - Acceptance of License Amendment Request to Revise Technical Specifications Consistent with TSTF-541, Revision 2 ML20136A5162020-05-15015 May 2020 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 and 2 - Acceptance of License Amendment Request to Revise Technical Specifications Consistent with TSTF-412, Revision 3 ML20133J9662020-05-11011 May 2020 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit No. 1 - Acceptance of License Amendment Regarding Changes to Reactor Vessel Heatup and Cooldown Curves and Low Temperature Overpressure Protection System Requirements ML20232B4562020-04-27027 April 2020 Request for Supporting Information for the D.C. Cook SPRA Audit Review - Fragility Questions ML20232B4432020-03-25025 March 2020 Request for Supporting Information for the D.C. Cook SPRA Audit Review - Plant Response Model Questions ML19345F9382019-12-0909 December 2019 D.C. Cook 50.54(f) SPRA Submittal - Completeness Review Done and Path Forward ML19333B8042019-11-29029 November 2019 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 and 2 - Acceptance Review for LAR to Adopt TSTF-569 (L-2019-LLA-0248) ML19309F9212019-11-0505 November 2019 Request for Eportal Access for Audit Review of the DC Cook SPRA Supporting Documents ML19270E7372019-09-26026 September 2019 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 and 2 - Acceptance Review for LAR to Adopt TSTF-421, Reactor Coolant Pump Flywheel Inspection Program ML19207A4642019-07-26026 July 2019 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 and 2 - Acceptance Review for LAR to Delete Diesel Generator Load Test Resistor Banks ML19204A0962019-07-23023 July 2019 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 and 2 - Request for Additional Information Related to Unit 2 Leak Before Break Analysis and Deletion of Containment Humidity Monitors for Unit Nos. 1 and 2 ML19211C3032019-07-0303 July 2019 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 & 2 - Request for Additional Information Related to LAR to Address NSAL-15-1 ML19175A3032019-06-24024 June 2019 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit No. 2 - Acceptance Review for LAR to Revise Battery Monitoring and Maintenance TS ML19092A4802019-04-0202 April 2019 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 and 2 - Acceptance Review for LAR to Adopt TSTF-563 ML19092A4792019-04-0202 April 2019 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 and 2 - Acceptance Review for LAR to Address Issues Identified in Westinghouse Document NSAL-15-1 ML19084A0002019-03-20020 March 2019 NRR E-mail Capture - Resubmitted: Draft Request for Additional Information DC Cook Unit 1 - Leak-Before-Break LAR ML19072A1432019-03-12012 March 2019 NRR E-mail Capture - Resubmitted: Draft Request for Additional Information DC Cook Unit 1 - Leak-Before-Break LAR ML19011A1382019-01-11011 January 2019 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 and 2 - Acceptance Review for LAR to Revise Environmental Technical Specifications (L-2018-LLA-0570) ML19011A3512019-01-11011 January 2019 NRR E-mail Capture - Request for Additional Information DC Cook Unit 1 Leak Before Break Amendment ML19009A5402019-01-0909 January 2019 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 and 2 - Acceptance Review for LAR to Revise Battery Monitoring and Maintenance TS ML18313A0802018-11-0808 November 2018 NRR E-mail Capture - D.C. Cook Units 1 and 2 - RAI for RPV Threads in Flange Alternative ML18275A0532018-10-0101 October 2018 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 and 2 - Acceptance Review for LAR to Revise Battery Monitoring and Maintenance TS 2023-02-21
[Table view] Category:Request for Additional Information (RAI)
MONTHYEARML23352A3502023-12-19019 December 2023 Dc. Cook Nuclear Power Plant, Units 1 Biennial Licensed Operator Requalification Program Inspection and Request for Information ML23310A1152023-11-0606 November 2023 Notification of the NRC Baseline Inspection and Request for Information, Inspection Report 05000316/2024002 ML22264A1112022-09-21021 September 2022 Notification of Post-Approval Site Inspection for License Renewal - Phase IV; IR 05000315/2023010; 05000316/2023010 and RFI ML22230A4362022-08-19019 August 2022 Licensed Operator Positive Fitness-For-Duty Test ML22049B4532022-02-22022 February 2022 Notification of NRC Baseline Inspection and Request for Information Report 05000315/2022002 ML21307A3352021-11-0303 November 2021 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 and 2 - Final RAI - License Amendment Request Regarding Containment Water Level Instrumentation ML21215A1242021-08-0303 August 2021 Information Request to Support Upcoming Temporary Instruction 2515/194 Inspection; Inspection Report 05000315/2021013; 05000316/2021013 ML21140A3052021-05-20020 May 2021 NRR E-mail Capture - Final RAI - D.C. Cook 1 & 2 - Relief Request ISIR-4-11, Impractical Examinations for the Fourth 10-Year ISI Interval ML21049A2682021-02-16016 February 2021 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit No. 2 - Final RAI - License Amendment Request for One-Time Extension Containment Type a ILRT ML21026A3472021-01-26026 January 2021 NRR E-mail Capture - Final RAI - D.C. Cook 1 & 2 - Relief Request REL-PP2 for Pump and Valve IST Fifth 10-year Interval IR 05000315/20200112020-09-17017 September 2020 Information Request to Support Upcoming Temporary Instruction 2515/194 Inspection; Inspection Report 05000315/2020011; 05000316/2020011 ML20181A4122020-06-29029 June 2020 NRR E-mail Capture - Final RAI - D.C. Cook 1 - One-Time Extension, Containment Type a ILRT Frequency ML20232B4562020-04-27027 April 2020 Request for Supporting Information for the D.C. Cook SPRA Audit Review - Fragility Questions IR 05000315/20200202020-04-10010 April 2020 Units 1 and 2 - Information Request for NRC Triennial Evaluation of Changes, Tests, and Experiments (50.59) Baseline Inspection 05000315/2020020 and 05000316/2020020 ML20232B4432020-03-25025 March 2020 Request for Supporting Information for the D.C. Cook SPRA Audit Review - Plant Response Model Questions ML19267A1362019-09-24024 September 2019 NRC Information Request (September 23, 2019) - IP 71111.08 - DC Cook U2 - Documents Selected for Onsite Review (DRS-M.Holmberg) ML19204A0962019-07-23023 July 2019 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 and 2 - Request for Additional Information Related to Unit 2 Leak Before Break Analysis and Deletion of Containment Humidity Monitors for Unit Nos. 1 and 2 ML19211C3032019-07-0303 July 2019 NRR E-mail Capture - D.C. Cook Nuclear Plant Unit Nos. 1 & 2 - Request for Additional Information Related to LAR to Address NSAL-15-1 ML19084A0002019-03-20020 March 2019 NRR E-mail Capture - Resubmitted: Draft Request for Additional Information DC Cook Unit 1 - Leak-Before-Break LAR ML19072A1432019-03-12012 March 2019 NRR E-mail Capture - Resubmitted: Draft Request for Additional Information DC Cook Unit 1 - Leak-Before-Break LAR ML19011A3512019-01-11011 January 2019 NRR E-mail Capture - Request for Additional Information DC Cook Unit 1 Leak Before Break Amendment ML18313A0802018-11-0808 November 2018 NRR E-mail Capture - D.C. Cook Units 1 and 2 - RAI for RPV Threads in Flange Alternative ML18263A1542018-09-14014 September 2018 NRR E-mail Capture - D.C. Cook Unit No. 1 - RAI for Leak-Before-Break LAR ML18204A3722018-07-19019 July 2018 NRR E-mail Capture - D.C. Cook Unit No. 1 - RAI for Leak-Before-Break LAR ML18143B6292018-05-29029 May 2018 Dtf. RAI ML18142B5312018-05-29029 May 2018 Request for Additional Information Concerning 2017 Decommissioning Funding Status Report ML18060A0212018-02-28028 February 2018 Enclosurequest for Additional Information (Request for Additional Information Regarding Indiana Michigan Power Company'S Decommissioning Funding Update for Donald C Cook Nuclear Plant Units 1 and 2 ISFSI) ML18043A0092018-02-0909 February 2018 NRR E-mail Capture - DC Cook, Unit 2 - Request for Additional Information Regarding Reactor Vessel Internals Again Management Program ML17304A0102017-11-0101 November 2017 Unit Nos.1 and 2 - Request for Additional Information Regarding Generic Letter 2016-01, Monitoring of Neutron-Absorbing Materials in Spent Fuel Pools (CAC Nos. MF9444 and MF9445; EPID L-2016-LRC-0001) ML17249A7492017-08-28028 August 2017 E-Mail Sent August 28, 2017, Request for Information for Donald C. Cook Nuclear Power Plant, Unit 1 (Part B); Inspection Report 05000315/2017004 (Msh) ML17108A7772017-04-18018 April 2017 17 Donald C. Cook Nuclear Power Plant, Unit 1 - Notification of NRC Baseline Inspection and Request for Information (05000315/2017003; 05000316/2017003) (Msh) ML17068A0652017-03-0808 March 2017 Ltr 03/08/17 Donald C. Cook Nuclear Power Plant, Unit 2 - Information Request for an NRC Post-Approval Site Inspection for License Renewal 05000316/2017009 (Bxj) ML17027A0192017-01-26026 January 2017 NRR E-mail Capture - D.C. Cook Units 1 and 2 - RAI Regarding LAR to Revise TS 5.5.14 (MF8483 and MF8484) ML16211A0152016-08-0101 August 2016 Follow-Up Request for Additional Information Regarding License Amendment Request to Relocate Surveillance Frequencies to Licensee Control IR 05000315/20160042016-07-11011 July 2016 Donald C. Cook Nuclear Power Plant, Unit 2 - Notification of NRC Inspection and Request for Information; Inspection Report 05000315/2016004; 05000316/2016004 ML16193A6542016-07-11011 July 2016 Notification of NRC Inspection and Request for Information; Inspection Report 05000315/2016004; 05000316/2016004 ML16154A1822016-06-0909 June 2016 Request for Additional Information Regarding License Amendment Request to Relocate Surveillance Frequencies to Licensee Control (CAC Nos. MF7114 and MF7115) ML16127A0792016-05-11011 May 2016 Request for Additional Information Regarding License Amendment Request to Relocate Surveillance Frequencies to Licensee Control ML16025A0552016-01-22022 January 2016 Ltr. 01/22/16 Donald C. Cook Nuclear Power Plant, Units 1 and 2 - Request for Information for an NRC Pilot Design Bases Inspection on the Implementation of the Environmental Qualification Program Inspection Report 05000315/2016008; 05000316 ML15267A6832015-10-0505 October 2015 Second Request for Additional Information Regarding License Amendment Request to Revise Technical Specification 3.8.1 ML15231A5542015-08-18018 August 2015 Ltr. 08/18/15 Donald C. Cook Nuclear Power Plant, Units 1 and 2 - Request for Information for an NRC Triennial Pilot Baseline Component Design Bases Inspection (Inspection Report 05000315/2015008; 05000316/2015008) (Axd) ML15225A5772015-08-13013 August 2015 Information Request to Support Upcoming Problem Identification and Resolution Inspection at D.C. Cook, Units 1 and 2 ML15163A1672015-06-15015 June 2015 Request for Additional Information Regarding License Amendment Request to Revise Technical Specification 3.8.1 ML15149A3832015-05-28028 May 2015 Information Request to Support NRC Annual Baseline Emergency Action Level and Emergency Plan Changes Inspection (Mxg) ML15119A3392015-05-0505 May 2015 Follow-up Request for Additional Information Concerning the Reactor Vessel Internals Aging Management Program Submittal ML15055A5702015-02-24024 February 2015 Cyber Security RFI Temporary Instruction 2201/004 ML15022A1532015-01-21021 January 2015 Dccook ISI Request for Information ML14363A4912015-01-16016 January 2015 DC Cook Nuclear Plant, Units 1 and 2 - Supplemental Information Needed for Acceptance of Requested Licensing Action to Adopt TSTF-490, Rev.0, Deletion of E-Bar Definition and Revision to Reactor Coolant System Specific Activity Technical Sp ML14246A4992014-08-26026 August 2014 NRR E-mail Capture - Donald C. Cook Nuclear Plant, Units 1 and 2 - Draft Requests for Additional Information (Scvb) Change to TS 5.5.14 by Adopting NEI 94-01, Revision 3-A ML14135A3202014-06-0606 June 2014 Request for Additional Information Concerning the Reactor Vessel Internals Afing Management Program Submittal 2023-12-19
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Text
From: Philpott, Stephen To: David L Williams Cc: Valentin-Olmeda, Milton
Subject:
Request for Supporting Information for the D.C. Cook SPRA Audit Review Date: Wednesday, March 25, 2020 11:24:00 AM Good morning Dave, The purpose of this email is to request the following information to support the audit review of the Donald C. Cook Nuclear Plant, Units 1 and 2 (CNP) 50.54(f) seismic probabilistic risk assessment (SPRA) submittal dated November 4, 2019 (ADAMS Accession No. ML19310D805). The NRC staff is using a technical checklist (see ADAMS Accession No. ML18173A017) to guide this review. The following audit questions will support this effort. Please provide your responses to the following questions via your Scientech (OneCWCloud) e-Portal SPRA audit site.
Donald C. Cook Nuclear Plant, Units 1 and 2 (CNP)
Plant-Response Model Questions Question 1 - Topic #12 - Selection of Dominant Risk Contributors that Require Fragility Analysis Using the Separation of Variables Methodology (SPID Section 6.4.1)
Section 4.4.1 of the submittal states that once dominant contributors were identified they were subject to refined analysis methods detailed in EPRI TR-103959 using the separation of variables (SOV) approach.However, the fragilities for over one-half of the top 10 seismic-induced failures reported in Tables 5.4-2 and 5.5-2 of the submittal used refined CDFM, judgement, and screened fragilities. This issue was the topic of SPRA peer review Facts and Observations (F&Os) 22-2 and 22-5. The recommended closeout of F&Os 22-2 and 22-5 requested a fragility sensitivity analyses on SCDF and SLERF be performed for the remaining risk important SSCs that do not have a refined analysis. The NRC staff reviewed the sensitivities provided in Section 5.7 of the submittal where Am values were increased by 50 percent for these SSCs (Case 14c). It is unclear to the NRC staff whether the modeling of these SSCs is masking the risk importance of other SSCs. In light of these observations, provide Tables 5.4-2 and 5.5-2 for the case 14.c sensitivity study and discuss the significance of these results to the SPRA submittals conclusion.
Question 2 - Topic #12 - Selection of Dominant Risk Contributors that Require Fragility Analysis Using the Separation of Variables Methodology (SPID Section 6.4.1)
Tables 5.4-2 and 5.5-2 provide risk significant SSCs for Unit 1. However, no Unit 2 risk-significant SSC results were provided. The licensee states in Sections 5.4 and 5.5 of the submittal that even though there are small numerical differences, the risk insights from Unit 1 are applicable to Unit 2.
However, Section 8.2 of the CNP SPRA Quantification Notebook details the modeling differences between Units 1 and 2. Some examples are that the same relay fragility groups have different failure probabilities, there are several asymmetries in the instrument air and 600vDC systems, differences in fire impacts, and additional differences in safe shutdown seal failures. In addition, Section 5.3 of the CNP SPRA Quantification Notebook states that Unit 2 SCDF and SLERF Fussell-Veseley (F-V) are within 2 and 4 percent of Unit 1.In light of these observations, identify any risk-significant Unit 2 SSCs that are not on the Unit 1 list, provide F-Vs for these SSCs, and discuss the impact of these SSCs to the SPRA submittals conclusions.
Question 3 - Topic #14 - Peer Review of the Seismic PRA, Accounting for NEI 12-13 (SPID Section 6.7)
Section 5.1 of the submittal states that the internal events F&O dispositions are provided in Appendix B of the CNP SPRA Model Notebook. In reviewing this appendix and open F&Os 2-10 and HR-B2-01, regarding Pre-initiator HRA, it was determined that several updates were made to the IEPRA HRA and that they were incorporated into the SPRA model used for the submittal.
However, Section 5.1 of the CNP SPRA HRA Notebook states that all internal events pre-initiator Human Failure Events (HFEs) were screened from the SPRA model. Therefore, it is unclear to the NRC staff the status of the pre-initiator HFEs in the SPRA model and if they were screened out or used.In light of these observations:
- a. Provide clarification on the status of the internal events PRA pre-initiator HFEs in the SPRA model.
- b. If not included in the SPRA model, provide justification for excluding
pre-initiator HFEs from the seismic analysis.Also provide justification, such as a sensitivity study, that the exclusion of the pre-initiator HFEs does not impact the results of the submittal.
Question 4 - Topic #15 - Documentation of the Seismic PRA (SPID Section 6.8)
Tables 5.4-1 and 5.5-1 of the submittal summarize the top ten SCDF and SLERF cutsets, respectively. During the review it was noted that the multiplication of the basic event (BE) probabilities in the cutset did not match the cutset probability. During the audit, Section 8.1 of the CNP SPRA Quantification Notebook was reviewed, which states that BEs that begin with a hyphen - are complement events and that the BE probability for the complements presented in the cutset are the failure probabilities. Therefore, the success probability used in the cutset requires an additional calculation (e.g., success probability = 1 - failure probability). The NRC staff was able to confirm the cutset probabilities when using the success probabilities based on the cutset descriptions provided in the SPRA Quantification Notebook.
However, there appears to be inconsistencies with the application of the success logic. Section 5.2.3.3 of the CNP SPRA Modeling Notebook states that seismic failure of either the screenhouse, main control boards, reactor coolant system (RCS) piping and significant LOCAs, RCS accumulators, reactor coolant pumps, or the polar crane lead directly to core damage (D-CD).
One SCDF cutset, Cutset #2 in Table 5.4-1 of the Submittal, contains only the seismic failure of the auxiliary building that leads directly to core damage and contains no success BEs. This appears to be contrary to the D-CD scenarios listed in the CNP SPRA Modeling Notebook. But the corresponding SLERF cutset is in accordance with the CNP SPRA Modeling Notebook since it identifies direct large early release (D-LER) failures that include the auxiliary and containment buildings seismic failures. The screenhouse cutset (Cutset #1), which is stated as a D-CD event, contains three seismic success BEs, and this also appears to be contrary to the CNP SPRA Modeling Notebook criteria. The turbine building seismic failure cutset (Cutset #3) only has one failure event, which the staff understands would represent a D-CD, but the cutset contains fourteen success BEs. The other remaining cutsets have two to four failures and contain the same fourteen success BEs as seen in the turbine building failure cutset.
The application of success criteria for the screenhouse and turbine building appears to have been forwarded to the SLERF results (SLERF Cutsets #9 and 10, respectively).
Regarding SLERF, Table 7 of the CNP SPRA Modeling Notebook explains that, with the exception of direct-LERF items mapped in the seismic initiator event tree, the internal events LERF event tree remains untouched. During the review of Section 8.1.2 of the CNP SPRA Quantification Notebook that corresponded to Table 5.5-1 of the submittal, with the exception of D-LER events (Cutsets #1, 2, 4, 7, and 8), the following failures are apparently required for large early release (Cutsets #3, 5, 6, 9, and 10): containment failure due to early RCS pressure high with late depressurization, pressurizer PORV or safety valve stuck open, and RCS depressurized prior to vessel breach (note: these three BEs do not appear in any SCDF cutset in Section 8.1.1).When reviewing SLERF Cutset #3, after removing the three LERF failure, initiator, and power availability events, the only remaining failures are the seismic-induced failure of both offsite power and the supplemental diesel.However, during the review of Section 8.1.1, no cutset had only those two failures leading to core damage.For example, SCDF Cutset
- 79, which represents the same seismic bin initiator and the same seismic failure of the supplemental diesel generator, also contained the seismic failures of Relay Groups B_2_U1 and B_5_U1. In applying the same approach to SLERF Cutsets #5 and 6, the path to core damage is seismic failure of offsite power and the ESW alignment being either east or west. It appears that SCDF Cutsets #22 and #23 are a match to these LERF sequences, but they require the additional seismic failures of Relay Groups D_1 and D_2. It is unclear to the NRC staff if the SLERF event tree, D-CD, and D-LER guidance of CNP SPRA Modeling Notebook is being appropriately implemented in the SPRA model.
In addition, these fourteen BEs represent seismic failure of the following SSCs:
RCS accumulators, main control room boards, small and medium LOCAs, polar crane, pressurizer supports, reactor coolant pump support system room, reactor pressure vessel, auxiliary building, screenhouse, containment, steam generators, containment elevation 625, and the auxiliary building valves.The NRC staff notes that most of the fourteen success BEs appear to be related to the D-CD seismic failure SSCs described in the CNP SPRA Modeling Notebook.
Given that the success BEs basically represent that this SSC did not seismically fail in an event tree logic sequence, this implies that the survival of that structure is required to implement a mitigation strategy used in the event tree.For many of the sequences there does not appear to be a causal relationship between the survival of a structure (or room) providing any mitigation of the initiator.In some cases, mitigation strategies are not available since the supporting operator action is not considered feasible (e.g., HEP is set to 1.). For example, the seismic failure of the turbine building that causes both a main steam line break and loss of mitigating strategies (submittal states that the mitigating operator actions are failed) appears to be a D-CD
event (Cutset #3),but the cutset includes the seismic survival of the same fourteen SSCs.However, with regard to other cutsets (that include seismic-induced loss of offsite power), structures that enclose the 250VDC and group B-2 relays and are impacted by internal flooding would have to survive the seismic event, but it is not apparent that the survival of these SSCs would depend on all fourteen SSCs surviving.
Section 5.2.8.1 of the CNP SPRA Modeling Notebook states that the two-top model is assembled by PRAQuant using the A AND not B logic structures where the A side represents the failures and the B side represents the success. The staff notes that this logic structure usually deletes from the resultant cutset file an A cutset sequence that matches a B sequence. In addition, the B side basic events would not appear in the results (similar to mutually exclusive logic). The staff is knowledgeable of the industry practice to include success probabilities to address the FTREX conservatism in using min cut upper bound (MCUB) calculations. However, the software program ACUBE was developed to address this issue and as stated in Section 5.3.2.3 of the submittal this program was used to quantify the SPRA model. It is unclear to the staff if this was the intended purpose of using success criteria logic.If application of the ACUBE software already accounts for the large overestimation of SCDF/SLERF from using MCUB on cutsets having success BEs, then the use of success BEs would appear to further lower the risk value (e.g., double counting) for the same issue. In light of these observations:
- a. Describe how success probabilities were determined and utilized in both the PRAQuant/CAFTA and ACUBE quantification.
- b. Provide the purpose, reasoning, and application of the use of success BE logic in the SPRA model. Include in this discussion how the guidance of the SPRA Modeling Notebook regarding D-CD and D-LER is reflected in the success logic of the SPRA model.
- c. Provide clarification of how core damage accident sequences, including their failure probabilities, are reflected in the quantified SLERF cutsets.
- d. Provide justification for the use of success BEs that appear to be unrelated to the mitigation of the specific seismic accident sequence.Include in this discussion a description of the event
tree(s) that represents the use of success logic.
- e. Provide clarification if the use of success BEs in the SPRA model is to address MCUB issues and/or given the A AND not B logic, to ensure success sequences do not appear in the final results.Include in this discussion, related to the AND not logic, why do the success BEs appear in the cutset and effect the overall risk value. If used to address MCUB conservatisms, then provide justification that the use of success BEs does not impact the SPRA results when ACUBE is used for quantification.
- f. Alternatively, if either the use of success BEs cannot be justified, is not appropriately applied, or is no longer required, then appropriately update the SPRA model logic and provide updated SPRA results.
Question 5 - Topic #16 - Review of Plant Modifications and Licensee Actions, If Any Section 6 of the submittal states that I&M plans to develop and implement a plant modification that will provide supplemental power to the containment DIS (hydrogen igniters) that mitigates loss of offsite power (LOOP). However, no details were provided in the submittal about this modification.
Provide the implementation schedule for this modification, details of the plant modification, assumptions that went into the sensitivity for the 50% SLERF risk reduction, and how the design will ensure the validity of the assumptions associated with this modification.
Please let me know when the responses are made available so that we can proceed with the audit review. If a conference call would be helpful to clarify or further explain any of these audit question, please let me know and I will be happy to arrange a call.
Also, we may have additional questions related to the fragility aspects of the SPRA, which I will send later.
Thank you, Steve Steve Philpott Project Manager Nuclear Regulatory Commission (NRR/DORL/LPMB) phone: 301-415-2365 e-mail:Stephen.Philpott@nrc.gov