ML17318A035

Request for Additional Information

ML17318A035
Person / Time
Site:	Vogtle
Issue date:	11/22/2017
From:	Marshall M Plant Licensing Branch 1
To:	Hutto J Southern Nuclear Operating Co
Orenak, M D, NRR/DORL/LPLII-1, 415-3229
References
CAC MF9685, CAC MF9686, EPID L-2017-TOP-0038
Download: ML17318A035 (6)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 November 22, 2017 Mr. James J. Hutto Regulatory Affairs Director Southern Nuclear Operating Co., Inc.

P.O. Box 1295, Bin 038 Birmingham, AL 35201-1295

SUBJECT:

VOGTLE ELECTRIC GENERATING PLANT, UNITS 1 AND 2 - REQUEST FOR ADDITIONAL INFORMATION (CAC NOS. MF9685 AND MF9686; EPID No. L-2017-TOP-0038)

Dear Mr. Hutto:

By letter dated April 21, 2017 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML17116A096) as supplemented by letters dated July 11, 2017 (ADAMS Accession No. ML17192A245) and November 9, 2017 (ADAMS Accession No. ML17314A014), Southern Nuclear Operating Company, Inc. submitted a plant-specific technical report (TR) for Vogtle Electric Generating Plant, Units 1 and 2 , and requested U.S. Nuclear Regulatory Commission (NRC) approval of the methods and inputs described in the TR. The plant-specific TR describes a risk-informed methodology to evaluate debris effects with the exception of in-vessel fiber limits.

The NRC staff has reviewed the submittal and has determined that additional information is needed to complete its review. Enclosed is the NRC staff's request for additional information (RAI). The RAls were discussed with your staff on November 13, 2017, and it was agreed that your response would be provided within 45 days from the date of this letter.

If you have any questions regarding this request, please contact me at (301) 415-2871 or Michael.Marshall@nrc.gov.

Sincerely, Michael L. Marshall, Jr., Senior Project Manager Plant Licensing Branch I Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-424 and 50-425

Enclosure:

Request for Additional Information

REQUEST FOR ADDITIONAL INFORMATION REGARDING SYSTEMATIC RISK-INFORMED ASSESSMENT OF DEBRIS TECHNICAL REPORT SOUTHERN NUCLEAR OPERATING COMPANY, INC.

VOGTLE ELECTRIC GENERATING PLANT, UNITS 1 AND 2 SOUTHERN NUCLEAR OPERATING COMPANY DOCKET NOS. 50-424 AND 50-425 By letter dated April 21, 2017 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML17116A096) as supplemented by letters dated July 11, 2017 (ADAMS Accession No. ML17192A245) and November 9, 2017 (ADAMS Accession No. ML17314A014), Southern Nuclear Operating Company, Inc. submitted a plant-specific technical report (TR) for Vogtle Electric Generating Plant, Units 1 and 2, (VEGP) and requested U.S. Nuclear Regulatory Commission (NRC) approval of the methods and inputs described in the TR. The plant-specific TR describes a risk-informed methodology to evaluate debris effects with the exception of in-vessel fiber limits.

The NRC staff reviewed the submittal and has determined that the enclosed additional information is needed to complete its review. The requests for additional information (RAls) listed below are not a complete listing of the additional information needed to complete the NRC staff's review. Additional RAls will be provided via separate correspondence. RAls number 1 through 3 were sent in a separate letter dated October 12, 2017 (ADAMS Accession No. ML17264A282). RAls number 4 through 1O were sent in a separate letter dated November 15, 2017 (ADAMS Accession No. ML17275A026).

Unless stated otherwise, all references to enclosures, sections, and page numbers in the RAls are concerning the letter dated April 21, 2017.

(11) It is stated in Enclosure 1, Section 7.0, "Quality Assurance" (QA) that:

... most of the analysis and testing for the risk-informed Generic Safety Issue (GSl)-191 evaluation was performed as safety related under vendor QA programs compliant with Title 10 of the Code of Federal Regulations (10 CFR) Part 50 Appendix B.

While this section describes exceptions regarding specific equations within the NARWHAL software, explicit discussion of quality assurance measures associated with the software development was not included.

a. Please describe quality assurance procedures taken (e.g., validation and verification processes) to ensure the NARWHAL software produces high fidelity results.

Enclosure

b. Please describe tests of BADGER software performed to verify that the total debris monotonically increases with break size.

(12) Enclosure 3, Section 13.1, "NARWHAL Software," states that the plant, at any given time, can be defined by a state vector (i.e., collection of parameters). A series of marching algorithms, constituting the core framework of NARWHAL software, are used to update the state vector by determining the amount of change in each variable given a change in time. While the submittal describes certain assumptions regarding parameters over times (e.g., instantaneous, 7.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />, etc.), the computer time step associated with the marching algorithms is not stated, nor is the dependence of the results on computer time-stepping.

Please describe the time step(s) used in executing the marching algorithms and whether those time steps are sufficient to ensure convergence of the results to capture the pertinent GSl-191 phenomena modeled properly (e.g., time evolution of head loss and in-core fiber penetration).

(13) Table 3-5 of Enclosure 3, Section 14.1, "VEGP NARWHAL CFP Evaluaion," provides NARWHAL software conditional failure probability (CFP) values for Strainer A and B, Strainer A only, and Strainer B only. Given that asymmetric transport may actually occur, but is not modeled in NARWHAL (page E2-51, Enclosure 5) demonstrate that NARWHAL calculations of CFP yield conservative values of (or have a negligible impact on) delta Core Damage Frequency (CDF) (i.e., ~CDF) and Large Early Release Frequency (LEAF).

(14) It is described in Enclosure 3, Section 14.2, "NARWHAL Uncertainty and Sensitivity," that competing factors affecting delta CDF (i.e., ~CDF), as summarized in the tornado diagram in Figure 3-9 and in Tables 3-13 and 3-14.

Please explain the competing physical processes that determine the "bounding direction" for the following entries:

• Tables 3 pool volume, pool temperature, secure containment spray time, pH.

• Table 3 pool volume, pool temperature, emergency core cooling system flow rate, pH.

(15) Enclosure 1, Attachment 3, "Resolution of the VEGP Seismic PRA Peer Review Findings,"

provides a description of peer review facts and observations (F&Os) and their disposition to support the application of the seismic probabilistic risk assessment (SPRA) to risk-informed systematic assessment of debris.

a. The VEGP SPRA peer review was performed using the process defined in Nuclear Energy Institute (NEI) 12-13, August 2012, "External Hazards PRA Peer Review Process Guidelines," (ADAMS Accession No. ML12240A027). While NEI 12-13 follows a process, which is similar to NRC endorsed peer review processes, NEI 12-13 has not been endorsed by the NRC. The NRC staff provided comments on NEI 12-13 via a letter dated November 16, 2012 (ADAMS Accession No. ML12321A280). Further, the letter stated that the NRC staff's comments on NEI 12-13:

... could impact the integrity and quality of the peer-review process, which could also affect the confidence the NRC has in establishing the technical

adequacy of licensee probabilistic risk assessments (PRAs) using this guidance ...

Please provide the following additional information to justify the use of NEI 12-13:

i. Please describe how the qualifications of the VEGP SPRA peer review team comply with the peer review requirements in Sections 1-6.2 and 5-3.2 of the American Society of Mechanical Engineers (ASME)/American Nuclear Society (ANS) PAA Standard (RA-Sa-2009) as endorsed in Regulatory Guide (RG) 1.200, Revision 2, "An Approach for Determining the Technical Adequacy of Probabilistic Risk Assessment Results for Risk-Informed Activities" (ADAMS Accession No. ML090410014).

ii. Please identify the unreviewed analysis methods (UAMs) used in the VEGP SPRA as determined by the peer review team and describe each UAM, including bases and any supporting analyses.

iii. Please describe if the VEGP SPRA relies on expert judgement to meet any supporting requirement (SR) and if so, demonstrate conformance to the expert judgment requirements of Section 1-4.3 of the 2009 ASME/ANS PAA Standard (RA-Sa-2009). Cite any information from the peer review report related to the evaluation of the use of expert judgment by the peer review team and whether the peer review team found the use of expert judgment to be appropriate.

iv. Please clarify whether VEGP SPRA was reviewed against Capability Category (CC) I for any SR. Provide a list of all SRs that were reviewed against CC I or found to meet only CC I without an associated finding. For each such SR, justify why not meeting the SR at CC II does not impact this application of VEGP SPRA to the risk-informed systematic assessment of debris.

v. Please clarify whether an "in-process" peer review was performed for the VEGP SPRA. If an "in-process" peer review was utilized, confirm that:

1. The approach met the requirements for an independent peer review as stated in ASME/ANS PAA Standard (RA-Sa-2009) and as endorsed in RG 1.200, Revision 2, and the process described in NEI 12-13.

2. A final review by the entire peer review team occurred after the completion of the SPRA.

3. Peer reviewers remained independent throughout the PAA development activity.

b. In RG 1.200, Revision 2, the NRC states:

For each application that calls upon this regulatory guide, the applicant identifies the key assumptions and approximations relevant to that

application. This will be used to identify sensitivity studies as input to the decision-making associated with the application.

Enclosure 3, Section 14.3, describes the SPRA models assumptions and sources of uncertainty. Table 3-19 in Enclosure 3 does not describe any specific uncertainty that was considered for the application of the SPRA to support the risk-informed systematic assessment of debris or the impact on this application.

Please describe the key assumptions and sources of uncertainties associated with the VEGP SPRA that were considered for this application and how their impact on the GSl-191 results was addressed.

c. In Attachment 3 of Enclosure 1, F&O 16-11, states that the review of the potential for additional dependencies introduced by the SPRA model is missing. The resolution states that the dependency analysis has been performed using the Electric Power Research Institute (EPRI) human reliability analysis (HRA) Calculator. The "Suggested Finding Resolution" states that the licensee plans to transition to a different dependency analysis method based on the EPRI HRA calculator. The 2009 ASME/ANS PRA Standard (RA-Sa-2009) defines a PRA upgrade as:

... incorporation into a PRA model of a new methodology or significant changes in scope or capability that impact the significant accident sequences or the significant accident progression sequences.

Non-mandatory Appendix 1-A of ASME/ANS PRA Standard (RA-Sa-2009) identifies "a different HRA approach to human error analysis ... " as a potential PRA upgrade. Based on Section 1-5, "PRA Configuration Control," of ASME/ANS PRA Standard (RA-Sa-2009) and RG 1.200, Revision 2, Regulatory Position 1.4, "PRA Development, Maintenance, and Upgrade," performance of a peer review of a PRA upgrade is identified as one of the characteristics and attributes of an acceptable process for maintaining and upgrading a PRA.

i. Please justify why the use of the EPRI HRA Calculator in the VEGP SPRA is not considered a PRA upgrade requiring a focused-scope peer review. In the justification, include a comparison of the implemented methods and base values for the top 25 human error probabilities (HEPs), as well as HRA dependencies.

ii. If not part of the top 25 HEPs, pre- and post-Calculator, please demonstrate that the same methods, steps, and sequence that had been used in the pre-existing, manual HRA calculations were exactly mirrored when adopting the HRA Calculator.

iii. If this change qualifies as an upgrade, please provide the results from of the focused-scope peer review addressing the associated F&Os and their resolutions.

ML17318A035

• via email OFFICE NRR/DORL/LPL 1/PM NRR/DORL/LPL2-1/PM NRR/DORL/LPL2-1 /LA NRR/DSS/APLB/TL(A)*

NAME MMarshall MOrenak KGoldstein Slyons DATE 11/16/2017 11/20/2017 11/16/17 10/12/2017 OFFICE NRR/DORL/LPL2-1/BC NRR/DORL/LPL 1/PM NAME MMarkley MMarshall DATE 11/22/2017 11/22/2017