ML17265A014

NRR E-mail Capture - Request for Additional Information - License Amendment Request for Transition to Westinghouse Core Design and Safety Analyses

ML17265A014
Person / Time
Site:	Wolf Creek
Issue date:	09/21/2017
From:	Balwant Singal Plant Licensing Branch IV
To:	Muilenburg W Wolf Creek
References
MF9307
Download: ML17265A014 (5)

Text

1 NRR-PMDAPEm Resource From:

Singal, Balwant Sent:

Thursday, September 21, 2017 2:53 PM To:

Muilenburg William T (wimuile@WCNOC.com)

Cc:

'Good Nicole R'; Pascarelli, Robert

Subject:

Request for Additional Information - License Amendment Request for Transition to Westinghouse Core Design and Safety Analyses (CAC No. MF9307)

Attachments:

MF9307-RAIs-SNPB.docx By letter dated January 17, 2017 (Agencywide Documents Access and Management System (ADAMS)

Accession No. ML17054C103, Package), as supplemented by letter dated May 4, 2017 (ADAMS Accession No. ML17130A915), Wolf Creek Nuclear Operating Corporation (WCNOC) submitted License Amendment Request (LAR) to transition to Westinghouse Core design and Safety Analyses (including adoption of Alternative Source Term) for Wolf Creek Generating Station (WCGS).

The U.S. Nuclear Regulatory Commission (NRC) staff is in the process of reviewing the subject LAR and has identified the need for additional information described in the attachment to this e-mail. Draft Request for Additional Information (RAI) was transmitted on September 13, 2017 and a clarification was held on September 21, 2017. It was agreed that WCNOC will provide response to these RAIs within 30 days from the date of this e-mail. Please treat this e-mail as transmittal of official RAIs.

Please note that several technical branches have been assigned for review of this LAR and this is only a partial request.

Balwant K. Singal Senior Project Manager (Diablo Canyon and Wolf Creek)

Nuclear Regulatory Commission Division of Operating Reactor Licensing Balwant.Singal@nrc.gov Tel: (301) 415-3016 Fax: (301) 415-1222

Hearing Identifier:

NRR_PMDA Email Number:

3739 Mail Envelope Properties (957801e88403480386c18cbd3ff8b5ea)

Subject:

Request for Additional Information - License Amendment Request for Transition to Westinghouse Core Design and Safety Analyses (CAC No. MF9307)

Sent Date:

9/21/2017 2:52:34 PM Received Date:

9/21/2017 2:52:35 PM From:

Singal, Balwant Created By:

Balwant.Singal@nrc.gov Recipients:

"'Good Nicole R'" <nilyon@WCNOC.com>

Tracking Status: None "Pascarelli, Robert" <Robert.Pascarelli@nrc.gov>

Tracking Status: None "Muilenburg William T (wimuile@WCNOC.com)" <wimuile@WCNOC.com>

Tracking Status: None Post Office:

HQPWMSMRS05.nrc.gov Files Size Date & Time MESSAGE 1319 9/21/2017 2:52:35 PM MF9307-RAIs-SNPB.docx 27352 Options Priority:

Standard Return Notification:

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Recipients Received:

ZZZ

NUCLEAR PERFORMANCE AND CODE REVIEW BRANCH REQUEST FOR ADDITIONAL INFORMATION FOR TRANSITION TO WESTINGHOUSE METHODOLOGIES AND SAFETY ANALYSES INCLUDING ADOPTION OF ALTERNATIVE SOURCE TERM WOLF CREEK GENERATING STATION

1. Title 10 of the Code of Federal Regulations (10 CFR) Section 50.46(b)(5) requires that

[a]fter any calculated successful initial operation of the ECCS [emergency core cooling system], the calculated core temperature shall be maintained at an acceptably low value and decay heat shall be removed for the extended period of time required by the long-lived radioactivity remaining in the core. Additional guidance for the performance of long term core cooling (LTCC) analyses was provided in the Nuclear Regulatory Commission (NRC) staff letters dated August 1 and November 23, 2005 letters (References 1 and 2, respectively) to Westinghouse Electric Company, LLC (Westinghouse) listing concerns with, and suspending NRC approval for use of, the Westinghouse LTCC methodology documented in CENPD-254-P-A (Reference 3).

The licensee submitted analyses performed by Westinghouse, documented in Section 2.7.4.2 of WCAP-17658-NP (Reference 4). The analyses seek to demonstrate that LTCC will not be inhibited by precipitation of boric acid. Because the method, code(s),

and assumptions used to calculate core boric acid concentrations following a loss-of-coolant accident (LOCA) are not clearly documented in the licensees submittal, the NRC staff requests the following additional information regarding the method used to demonstrate adequate post-LOCA long term core cooling in compliance with the 10 CFR 50.46(b)(5).

a. Please identify and provide a technical description of the code used to perform the evaluation, which at a minimum should include a basic overview of the modeling, major assumptions, and any pre-or post-processing steps associated with the core boron concentration calculations.

b. Please provide a description of the void model used in the method, including a discussion of the conditions under which it was validated and whether the void calculation is axially dependent.

c. Please provide additional detail on the assumptions regarding reactor coolant system pressure and their impacts on the void calculations. The response should also include a discussion on how the loop pressure drop calculation requested in the NRC staff letters August 1, 2005 and November 23, 2005 (References 1 and 2) has been incorporated into the methodology.

d. Please provide additional detail on the regions of the vessel and core assumed to form the mixing volume, including assumptions regarding voiding in these regions.

e. Please provide a description of the method used to verify that sufficient decay heat removal will be provided after the initial switch to cold leg recirculation and the subsequent switch to hot leg injection.

2. Footnote 11 of Regulatory Guide (RG) 1.183 (Reference 5) contains acceptable gap release fractions for LOCA and non-LOCA transients in Section 3.2, Tables 2 and 3 (for pressurized water reactors). The gap fractions reported in this table assume a linear heat generation rate (LHGR) of 6.2 kilowatts per foot (kW/ft) for peak burnups beyond 54 gigawatt-days per metric ton of uranium (GWd/MTU). However, the footnote allows licensees to perform fission gas release calculations for the NRC staff to review on a case-by-case basis, provided that the calculations use a power history that bounds the limiting plant-specific power history.

The licensees fuel handling accident analysis methodology (reported in Reference 6),

stated that the assumed gap release fractions were based on values reported in NUREG/CR-5009 (Reference 7) for high burnup fuel. As discussed in a response to an NRC request for additional information (RAI), the licensee considers these gap fractions to be applicable up to a peak LHGR of 20.5 kW/ft for burnups exceeding 50 GWd/MTU (Reference 8). In Reference 9, the licensee justified the use of NUREG/CR-5009 gap fractions by comparing them to calculations performed using the ANSI/ANS-5.4-2011 standard for fission gas release, as documented in Reference 10.

However, Appendix A to Reference 10 indicates that the calculations the licensee compared the NUREG/CR-5009 gap fractions to, were performed using a maximum LHGR of 12.2 kW/ft that decreases with burnup to 7.0 kW/ft. The NRC staff is concerned that an assumed LHGR of 20.5 kW/ft for burnups up to 62 GWd/MTU is unrealistically high and that the gap fractions provided in NUREG/CR-5009 will not be applicable at such high power densities. Please provide further justification for the gap fractions assumed in the fuel handling accident analysis. The justification should provide an analysis using NRC-approved methodologies and a power history that bounds limiting plant-specific power histories at Wolf Creek, per RG 1.183 Footnote 11. One example of such an analysis that was recently accepted by the NRC is documented in Reference 11.

References

1. Gramm R., U. S. Nuclear Regulatory Commission, letter to J.A. Gresham, Westinghouse Electric Company, Suspension of NRC Approval for Use of Westinghouse Topical Report CENPD-254-P, Post-LOCA Long-Term Cooling Model, Due to Discovery of Non-Conservative Modeling Assumptions during Calculations Audit, dated August 1, 2005 (ADAMS Accession No. ML051920310).

2. Collins D., U. S. Nuclear Regulatory Commission, letter to J.A. Gresham, Westinghouse, Clarification of NRC Letter Dated August 1, 2005, Suspension of NRC Approval for Use of Westinghouse Topical Report CENPD-254-P, Post-LOCA Long-Term Cooling Model, Due to Discovery of Non-Conservative Modeling Assumptions during Calculations Audit, dated November 23, 2005 (ADAMS Accession No. ML052930272).

3. Scherer A., C-E Power Systems, Combustion Engineering, Inc., letter to U.S. Nuclear Regulatory Commission, Post-LOCA Long Term Cooling Evaluation Model, dated August 4, 1980, transmitting CENPD-254-P-A, June 1980 (ADAMS Accession No. ML15358A220, non-publicly available).

4. Westinghouse WCAP-17658-NP, September 2016, Revision 1-C, Wolf Creek Generating Station Transition of Methods for Core Design and Safety Analyses -

Licensing Report, (ADAMS Accession No. ML17054C224).

5. Regulatory Guide 1.183, Alternative Radiological Source Terms for Evaluating Design Basis Accidents at Nuclear Power Reactors, July 2000 (ADAMS Accession No. ML003716792).

6. Westinghouse Report, Full Scope Implementation of Alternative Source Term, November 2016, (ADAMS Accession No. ML17054C227).

7. NUREG/CR-5009 (PNL-6258), Assessment of the Use of Extended Burnup Fuel in Light Water Power Reactors, February 1988 (Legacy Accession No. 8802240276).

8. McCoy J., Wolf Creek Nuclear Operating Corporation, letter to U. S. Nuclear Regulatory Commission, Docket No. 50-482: Response to Supplemental Information Needed for Acceptance of Requested Licensing Action Re: Transition to Westinghouse Core Design and Safety Analyses, dated May 4, 2017 (ADAMS Accession No. ML17130A915).

9. Westinghouse document LTR-OPB-PMO-MEP-16-017, Revision 2, Responses to NRC RAIs on August 2013 Methodology Transition LAR Submittal (Non-Proprietary),

November 2016 (ADAMS Accession No. ML17054C229).

10. Pacific Northwest National Laboratory Report PNNL-18212, Revision 1, Update of Gap Release Fractions for Non-LOCA Events Utilizing the Revised ANS 5.4 Standard, June 2011 (ADAMS Accession No. ML112070118).

11. Hall J., U. S. Nuclear Regulatory Commission, letter to R.T. Repko, Duke Energy, Catawba Nuclear Station, Units 1 and 2; McGuire Nuclear Station, Units 1 and 2; and Oconee Nuclear Station, Units 1, 2, and 3 - Issuance of Amendments Regarding Request to Use an Alternate Fission Gas Gap Release Fraction, dated July 19, 2016, (ADAMS Accession No. ML16159A336).