ML20143A169
| ML20143A169 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 05/28/2020 |
| From: | Kimberly Green Plant Licensing Branch II |
| To: | Jim Barstow Tennessee Valley Authority |
| Green K | |
| References | |
| EPID L-2020-LRM-0030 | |
| Download: ML20143A169 (4) | |
Text
May 28, 2020 LICENSEE:
Tennessee Valley Authority FACILITY:
Watts Bar Nuclear Plant, Unit 2
SUBJECT:
SUMMARY
OF MAY 14, 2020, TELECONFERENCE CALL WITH TENNESSEE VALLEY AUTHORITY REGARDING A PLANNED LICENSE AMENDMENT REQUEST FOR WATTS BAR NUCLEAR PLANT, UNIT 2 (EPID L-2020-LRM-0030)
On May 14, 2020, a Category 1 public teleconference call was held between the U.S. Nuclear Regulatory Commission (NRC) staff and representatives of Tennessee Valley Authority (TVA).
The purpose of the meeting was to discuss TVAs planned license amendment request (LAR) for Watts Bar Nuclear Plant (WBN), Unit 2. The LAR would seek to revise WBN Unit 2 Technical Specification (TS) 5.9.6, Reactor Coolant System (RCS) Pressure and Temperature Limits Report (PTLR), to add WCAP-18124-NP-A, Revision 0, Fluence Determination with RAPTOR-M3G and FERRET, as a neutron fluence calculational methodology for the evaluation of reactor vessel specimens to support determination of RCS pressure and temperature limits.
The meeting notice and agenda, dated April 24, 2020, are available at Agencywide Documents Access and Management System (ADAMS) Accession No. ML20134J090. TVAs slides for the meeting are available at ADAMS Accession No. ML20134J010. A list of participants is provided as an enclosure to this summary. No regulatory decisions were made at this meeting.
TVA began its presentation by providing a background on the regulations and regulatory guidance for fracture toughness requirements for reactor coolant pressure boundary materials.
TVA explained that the previous generation of computer codes for determining neutron fluence required extensive computational resources, that often resulted in the use of overly conservative simplifying assumptions. Therefore, to address the computational limitations, Westinghouse developed the RAPTOR-M3G computer code, which is described in WCAP-18124-NP-A, Revision 0. The NRC found this methodology acceptable for use in calculating reactor pressure vessel (RPV) neutron fluence provided that two limitations listed in Section 4.0 of the safety evaluation are met (ADAMS Accession No. ML18156A066).
TVA stated that WBN Unit 2 is a PTLR plant; therefore, the methods used for future changes to the PTLR must be approved for use by the NRC staff and listed in TS 5.9.6. TVA used the RAPTOR-M3G computer code to determine fluence values from the analysis of WBN Unit 2 Capsule U (ADAMS Accession No. ML20107F717). In accordance with Title10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix H, Item IV.A, TVA submitted the required report, which stated that a license amendment to incorporate this computer code into the WBN Unit 2 licensing basis was planned for submission later this year, which is the subject of this meeting.
Limitation 4.1 in the SE for WCAP-18124-NP-A, Revision 0, states that WCAP-18124-NP, Revision 0, is limited to the RPV region near the active height of the core based on the uncertainty analysis performed and the measurement data provided, and that additional justification should be provided via additional benchmarking, fluence sensitivity analysis, margin assessment, or a combination thereof. TVA stated that Limitation 4.1 has been addressed with additional justification provided by benchmarking and a margin assessment. The benchmarking was performed by comparing RAPTOR-M3G calculated fluence values to ex-vessel neutron dosimetry (EVND) measurements at another Westinghouse 4-loop plant. The EVND capsules were placed in the vicinity of the RPV supports in a comparable geometry to the region of interest for WBN Unit 2. TVA stated that a margin assessment was performed by taking RAPTOR-M3G calculated fluences for WBN Unit 2, increasing these values by appropriate factors based on benchmarking, and validating that the appropriate extended beltline materials have been identified for evaluation of fracture toughness embrittlement effect. The NRC staff asked what factor TVA increased the fluence by and what angular quadrature was used. TVA said that both values would be provided in the LAR.
Limitation 4.2 states that least squares adjustment is acceptable if the adjustments to the measured-to-calculated ratios and to the calculated spectra values are within the assigned uncertainties of the calculated spectra, the dosimetry measured reaction rates, and the dosimetry reaction cross sections. This limitation applies in situations where the least squares analysis is used to adjust the calculated values of neutron exposure. TVA stated that Limitation 4.2 does not apply because in the most recent analysis of a WBN Unit 2 surveillance capsule, the least squares analysis was used only as a supplemental check on the results of the dosimetry evaluation and not to modify the calculated surveillance capsule or reactor pressure vessel neutron exposure.
TVA stated that it will propose a revision to TS 5.9.6 to add WCAP-18124-NP-A, Revision 0, as an analytical method used to calculate RCS pressure and temperature limits and cold overpressure mitigation system setpoints. The NRC staff suggested that TVA may want to ensure that the proposed TS 5.9.6 references specify what WCAP-18124-NP-A is being used to calculate because Chapter 2 of WCAP-14040-A, Revision 4, Methodology Used to Develop Cold Overpressure Mitigating System Setpoints and RCS Heatup and Cooldown Limit Curves, which is referenced in TS 5.9.6, describes different transport methods to determine the fluence.
The staff suggested that identifying, in TS 5.9.6, that WCAP-18124-NP-A may be used in lieu of Chapter 2 of WCAP-14040-A would result in a clearer description of the overall methods used to create PTLRs in the future. TVA stated that it will consider the NRC staffs suggestion.
TVA plans to submit the LAR in June 2020 and will request approval within one year.
No comments or public meeting feedback were received.
Please direct any inquiries to me at 301-415-1627, or Kimberly.Green@nrc.gov.
/RA/
Kimberly J. Green, Senior Project Manager Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-391
Enclosure:
List of Participants cc: Listserv
Enclosure LIST OF PARTICIPANTS MAY 14, 2020, PUBLIC TELECONFERENCE CALL TENNESSEE VALLEY AUTHORITY REGARDING PLANNED LICENSE AMENDMENT REQUEST WATTS BAR NUCLEAR PLANT, UNIT 2 Name Organization Kim Green U.S. Nuclear Regulatory Commission (NRC)
Bob Lukes NRC Ben Parks NRC Kevin Heller NRC Ashley Smith NRC Josh Kaizer NRC John Lehning NRC Ravi Grover NRC Josh Wilson NRC Andy Taylor Tennessee Valley Authority (TVA)
Dean Baker TVA Charles Menke TVA Andrew Taylor TVA Russ Wells TVA Gordon Williams TVA
- via e-mail OFFICE NRR/DORL/LPL2-2/PM* NRR/DORL/LPL2-2/LA* NRR/DORL/LPL2-2/BC* NRR/DORL/LPL2-2/PM*
NAME KGreen BAbeywickrama UShoop KGreen DATE 05/26/2020 05/26/2020 05/27/2020 05/28/2020