ML21064A408

Correction of Safety Evaluation for License Amendment Nos. 143 and 50 (EPID L-2020-LLA-0005) (Non-Proprietary)

ML21064A408
Person / Time
Site:	Watts Bar
Issue date:	03/10/2021
From:	Kimberly Green Plant Licensing Branch II
To:	Jim Barstow Tennessee Valley Authority
Green K
Shared Package
ML21064A458	List: ML21064A408
References
EPID L-2020-LLA-0005
Download: ML21064A408 (6)

Text

OFFICIAL USE ONLY PROPRIETARY INFORMATION March 10, 2021 Mr. James Barstow Vice President, Nuclear Regulatory Affairs and Support Services Tennessee Valley Authority 1101 Market Street, LP 4A-C Chattanooga, TN 37402-2801

SUBJECT:

WATTS BAR NUCLEAR PLANT, UNITS 1 AND 2 CORRECTION OF SAFETY EVALUATION FOR LICENSE AMENDMENT NOS. 143 AND 50

Dear Mr. Barstow:

On February 26, 2021, the U.S. Nuclear Regulatory Commission (NRC) issued Amendment No. 143 to Facility Operating License No. NPF-90, and Amendment No. 50 to Facility Operating License No. NPF-96, for Watts Bar Nuclear Plant (Watts Bar), Units 1 and 2, respectively (Agencywide Documents Access and Management System (ADAMS) Accession No. ML21034A148 (Proprietary)).

Among other changes, the amendments revised the Watts Bar, Units 1 and 2, Technical Specification (TS) 5.9.5, Core Operating Limits Report, to replace the loss-of-coolant accident (LOCA) analysis evaluation model references with reference to the FULL SPECTRUM' Loss-of-Coolant Accident (FSLOCA') Evaluation Model analysis. The amendments also approved the use the new LOCA-specific tritium producing burnable absorber rod (TPBAR) stress analysis methodology to evaluate the integrity of the TPBARs for the conditions expected during a large-break LOCA and provide a recovery of margin in the post-LOCA criticality evaluation in the presence of assumed TPBAR failures.

A non-proprietary version of the amendments under ADAMS Accession No. ML21034A169 was prepared but not yet released to the public to allow Tennessee Valley Authority (TVA) the opportunity to confirm the proprietary markings in the safety evaluation (SE). On March 3, 2021, TVA staff notified the NRC staff of two statements in the SE that should have been marked as proprietary. These statements on SE pages 11 and 21 have been redacted and are incorporated in the non-proprietary version of Amendment Nos. 143 and 50, dated February 26, 2021, which was released to the public on March 5, 2021.

During its review, TVA identified two additional errors in the SE on pages 5 and 12. TVA indicated that in Section 3.1, Background, the last sentence of the second paragraph, These analyses are necessary to confirm that the amount of energy analyzed during the transient, Enclosure 2 to this letter contains proprietary information. When separated from Enclosure 2, this document is decontrolled.

OFFICIAL USE ONLY PROPRIETARY INFORMATION

OFFICIAL USE ONLY PROPRIETARY INFORMATION J. Barstow using FSLOCA, is valid and realistic, is not correct. Also, in Section 3.2.7, Summary and Conclusion for the LOCA-Specific TPBAR Stress Analysis Methodology, the phrase, which is relied upon in the FSLOCA analysis, in the last sentence of the paragraph is not correct.

Upon further review, the NRC staff determined that the two statements are inaccurate as written because the FSLOCA results are used in combination with the TPBAR stress analysis to evaluate post-LOCA subcriticality. Therefore, the NRC staff has determined these statements can be deleted from the SE without altering the staffs conclusions.

The NRC concludes that these corrections do not change the staffs previous conclusions in the SE, nor do they affect the no significant hazards consideration, as published in the Federal Register on June 2, 2020 (85 FR 33745). Enclosure 1 contains corrected pages 5 and 12 for the non-proprietary SE for Amendment Nos. 143 and 50. Enclosure 2 contains corrected pages 5, 11, 12, and 21 for the proprietary SE for Amendment Nos. 143 and 50. The corrections are denoted by a revision bar in the right margin.

If you have any questions regarding this matter, please contact me at (301) 415-1627 or by e-mail at Kimberly.Green@nrc.gov.

Sincerely,

/RA/

Kimberly J. Green, Senior Project Manager Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-390 and 50-391

Enclosures:

1. Correction to Non-Proprietary SE pages 5 and 12

2. Correction to Proprietary SE pages 5, 11, 12, and 21 cc without Enclosure 2: Listserv OFFICIAL USE ONLY PROPRIETARY INFORMATION

ENCLOSURE 1 CORRECTED PAGES 5 AND 12 FOR NON-PROPRIETARY SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 143 TO FACILITY OPERATING LICENSE NO. NPF-90 AND AMENDMENT NO. 50 TO FACILITY OPERATING LICENSE NO. NPF-96 TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT, UNITS 1 AND 2 DOCKET NOS. 50-390 AND 50-391 Proprietary information pursuant to Section 2.390 of Title 10 of the Code of Federal Regulations has been redacted from this document.

Redacted information is identified by blank space enclosed within (( double brackets )).

OFFICIAL USE ONLY PROPRIETARY INFORMATION

3.0 TECHNICAL EVALUATION

The NRC staff evaluated the licensee's LAR to determine whether the proposed changes would continue to meet the regulations and guidance provided in Section 2.2 of this safety evaluation.

The NRC staff reviewed the licensees proposed changes to verify that all limitations and conditions in applicable NRC-approved methods are met, the licensee appropriately applied the LOCA EM to Watts Bar, Units 1 and 2, and the acceptance criteria of 10 CFR 50.46(b)(1) through (4) are satisfied.

3.1 Background

TVA requested approval to use the FSLOCA EM to evaluate the peak cladding temperatures for large-break and small-break LOCAs. In addition, TVA requested approval to use the new TPBAR stress analysis methodology to provide a recovery of margin in the post-LOCA criticality evaluation in the presence of assumed TPBAR failures. TVA proposes to use the new LOCA-specific TPBAR stress analysis methodology to evaluate the integrity of the TPBARs for the conditions expected during a large-break LOCA (LBLOCA).

The presence of TPBARs in Watts Bar, Units 1 and 2 results in positive reactivity insertion following a LOCA in the event of cladding rupture at high temperatures. During a post-LOCA core uncovery, the overheating of fuel rods causes heating of the TPBARs located in adjacent control rod guide tubes. The heating of the TPBARs can result in rupture of the TPBAR cladding due to the increase in internal pressure. As a result of potential TPBAR cladding rupture, Li-6 (Lithium-6) will leak out near the rupture location and the potential for subsequent leaching of Li-6 in the long term. Lithium-6 is a neutron absorbing isotope and the loss of Li-6 results in positive reactivity addition. These TPBAR structural integrity analyses were used to demonstrate that the TPBARs remain intact following a LBLOCA. This demonstration is needed, because if a TPBAR loses its structural integrity, some of the lithium contained within can leach out, causing an increase in the reactivity in the core, and potentially adding heat.

The LOCA-specific TPBAR stress analysis methodology relies on conditions resulting from LBLOCA simulations generated according to the FSLOCA evaluation model. Application of new TPBAR LOCA-specific TPBAR stress analysis methodology requires survival ((

)) survival does not need to be demonstrated.

The following sections describe the LOCA-specific TPBAR stress analysis methodology, TPBAR cladding stress evaluation following an LBLOCA, TPBAR cladding acceptance criteria and methodology conservatisms, and stress analysis results.

3.2 LOCA-Specific TPBAR Stress Analysis Methodology The LOCA-specific TPBAR cladding stress analysis methodology is designed to determine the potential for TPBAR cladding mechanical rupture under LBLOCA temperature and differential pressure conditions. The LBLOCA for Watts Bar, Units 1 and 2 is analyzed using the WCOBRA/TRAC-TF2 thermal hydraulic code using the FSLOCA methodology to predict the response of fuel rods for cladding temperatures and oxidation following a postulated LOCA.

OFFICIAL USE ONLY PROPRIETARY INFORMATION

OFFICIAL USE ONLY PROPRIETARY INFORMATION In summary, the licensee stated that the 95/95 tolerance limits for (1) the primary membrane and bending stress safety factor, and (2) the creep damage ratio maintain significant margin to the burst stress failure criteria, and as such, there is very high confidence that the TPBARs will not rupture following a postulated LBLOCA.

Sensitivity studies for PWR parameters derived from a subset uncertainty analysis covering various designs and fuel were examined to determine the sensitivity of the analysis results to the error correction. The error correction was found to be different for different transient phases, blowdown versus reflood. Based on the results from the PWR sensitivity studies, the correction of the error is estimated to result in a fuel cladding temperature increase for the time period relevant to TPBAR structural integrity, which is assumed to also lead to a TPBAR cladding temperature increase. TPBAR structural integrity calculations were performed with an assumed increase in TPBAR temperature throughout the transient. The updated TPBAR structural integrity analysis results in acceptable 95/95 primary membrane and bending stress safety factor and 95/95 cumulative creep damage ratio as indicated in Table 4.3.2-1 of the LAR.

The NRC staff reviewed the results of TPBAR structural integrity analysis, including the sensitivity studies, and has determined that TPBARs will not rupture with 95/95 probability and confidence.

3.2.7 Summary and Conclusion for the LOCA-Specific TPBAR Stress Analysis Methodology The licensee has performed a TPBAR structural integrity analysis following a LOCA. The LOCA-specific TPBAR stress analysis methodology relies on conditions resulting from LBLOCA simulations according to the FSLOCA methodology. The NRC staff reviewed all the aspects of the TPBAR stress analysis for structural integrity such as the Watts Bar units core model, cladding stress analysis acceptance criteria, conservatism built into the integrity analysis, post-LOCA criticality analysis, and uncertainty analysis. The NRC staff also has determined that the licensees assumption that the TPBARs remain intact post-LOCA is acceptable.

3.3 Limitations and Conditions The safety evaluation for WCAP-16996-P-A, Revision 1 (Reference 17) contains 15 limitations and conditions that must be met in order for a licensee to be permitted to implement the NRC-approved FSLOCA EM.

A summary of each limitation and condition and how it has been met as stated by the licensee in its corrected application dated January 26, 2021, and the associated NRC staff findings are provided below.

3.3.1 Limitation and Condition Number 1 - Applicability with Regard to LOCA Transient Phases Condition The FSLOCA EM is not approved to demonstrate compliance with 10 CFR 50.46 acceptance criterion (b)(5) related to the long-term cooling.

OFFICIAL USE ONLY PROPRIETARY INFORMATION

OFFICIAL USE ONLY - PROPRIETARY INFORMATION J. Barstow

SUBJECT:

WATTS BAR NUCLEAR PLANT, UNITS 1 AND 2 - CORRECTION OF SAFETY EVALUATION FOR LICENSE AMENDMENT NOS. 143 AND 50 DATED MARCH 10, 2021 DISTRIBUTION:

PUBLIC/NON-PUBLIC PM File Copy RidsACRS_MailCTR Resource RidsNrrDorlLpl2-2 Resource RidsNrrPMWattsBar Resource RidsNrrLARButler Resource RidsRgn2MailCenter Resource RidsNrrDssSfnb Resource ADAMS Accession Nos.:

Package ML21064A458 Proprietary ML21064A406 Non-Proprietary ML21064A408 OFFICE NRR/DORL/LPL2-2/PM NRR/DORL/LPL2-2/LA NRR/DSS/SFNB/BC NAME KGreen RButler RLukes DATE 03/04/2021 3/8/2021 03/05/2021 OFFICE NRR/DORL/LPL2-2/BC NRR/DORL/LPL2-2/PM NAME UShoop KGreen DATE 03/09/2021 03/10/2021 OFFICIAL USE ONLY - PROPRIETARY INFORMATION