ML17053A106

Millstone Power Station, Units 2 & 3 - Response to Request for Additional Information Regarding Proposed Alternative Requests RR-04-24 and IR-3-30 for Elimination of the Reactor Pressure Vessel Threads in Flange Examination

ML17053A106
Person / Time
Site:	Millstone
Issue date:	02/16/2017
From:	Sartain M D Dominion, Dominion Nuclear Connecticut
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
17-048
Download: ML17053A106 (5)

Text

Dominion Nuclear Connecticut, Inc.

• 5000 Dominion Boulevard, Glen Allen, VA 23060 Web Address: www.dom.com U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 February 16, 2017 DOMINION NUCLEAR CONNECTICUT, INC. MILLSTONE POWER STATION UNITS 2 AND 3 Dominion Serial No.17-048 NRA/WDC RO Docket Nos. 50-336/423 . License Nos. DPR-65 NPF-49 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING PROPOSED ALTERNATIVE REQUESTS RR-04-24 and IR 30 FOR ELIMINATION OF THE REACTOR PRESSURE VESSEL THREADS IN FLANGE EXAMINATION By letter dated October 6, 2016, Dominion Nuclear Connecticut, Inc. (DNC) requested Nuclear Regulatory Commission (NRC) approval of Alternative Request RR-04-24, for Millstone Power Station Unit 2 (MPS2) and Alternative Request IR 30 for Millstone Power Station Unit 3 (MPS3). American Society of Mechanical Engineers (ASME) Code,Section XI requires a volumetric examination of Reactor Vessel -Threads in Flange to satisfy nondestructive examination requirements. DNC requested approval to eliminate the volumetric examination for the remainder of the fourth 10-year inservice inspection interval for MPS2 scheduled to end on March 31, 2020 and for the remainder of the third 10-year inservice inspection interval for MPS3 scheduled to end on April 22, 2019. In an email dated February 2, 2017, the NRC transmitted a request for additional information (RAI) related to the alternative requests. DNC agreed to respond to the RAI by March 2, 2017. The attachment to this letter provides the response to the RAI for MPS2 and MPS3. If you have any questions regarding this submittal, please contact Wanda Craft at (804) 273-4687. Sincerely, -Mark D. Sartain Vice President -Nuclear Engineering and Fleet Support

Attachment:

1. Response to Request for Additional Information Regarding Alternative Requests RR-04-24 and IR 30, Proposed Alternative to ASME Section XI for Elimination of Reactor Pressure Vessel Threads in Flange Examination Commitments made in this letter: None cc: U.S. Nuclear Regulatory Commission Region I 2100 Renaissance Blvd Suite 100 King of Prussia, PA 19406-2713 Richard V. Guzman Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08 C 2 11555 Rockville Pike . Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station Serial No.17-048 Docket Nos. 50-336/423 Page 2 of 2 ATTACHMENT Serial No.17-048 Docket Nos. 50-336/423 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING .ALTERNATIVE REQUESTS RR-04-24 AND IR 30, PROPOSED ALTERNATIVE TO ASME SECTION XI FOR ELIMINATION OF REACTOR PRESSURE VESSEL THREADS IN FLANGE EXAMINATION MILLSTONE POWER STATION UNITS 2 AND 3 DOMINION NUCLEAR CONNECTICUT, INC.

Serial No.17-048 Docket Nos. 50-336/423 Attachment, Page 1 of 2 By letter dated October 6, 2016, Dominion Nuclear Connecticut, Inc. (DNC) requested Nuclear Regulatory .Commission (NRC) approval of Alternative Request RR-04-24, for Millstone Power Station Unit 2 (MPS2) and Alternative Request IR 30 for Millstone Power Station Unit 3 (MPS3). American Society of Mechanical Engineers (ASME) Code,Section XI requires a volumetric examination of Reactor Vessel -Threads in Flange to satisfy nondestructive examination requirements. DNC requested approval to eliminate the volumetric examination for the remainder of the fourth 10-year inservice inspection interval for MPS2 scheduled to end on March 31, 2020 and for the remainder of the third 10-year inservice inspection interval for MPS3 scheduled to end on April 22, 2019. In an email dated February 2, 2017, the NRC transmitted a request for additional information (RAI) related to the alternative requests. This attachment provides DNC's response to the NRC's RAI. RAl-1 Table 2 of Attachments 1 and 2 of the submittal shows that most of the load comes from the preload on the bolt (bolt preload), which occurs at low temperature. However, the flaw tolerance evaluation only considers the fracture toughness (K1c) at the upper shelf (operating temperature). The NRG staff requests the licensee to provide a comparison between the calculated Table 2 "Preload" values of Kand the applicable allowable value for K for MPS2 and MPS3 at the head tensioning temperatures. DNC Response The fracture toughness (K1c) during head tensioning is based on the reference temperature for nil ductility transition (RTndt) of the vessel flange materials, the assumed flange temperature at the time of head tensioning, and the correlation for K1c provided in Figure A-4200-1 of ASME Code,Section XI. The RTndt of the vessel flange region is 10 degrees F as reported in FSAR Table 4.6-1 for MPS2 and minus 40 degrees F as reported in FSAR Table 5.3-2 for MPS3. Head tensioning for both units occurs at 70 degrees F or above. For MPS2, which bounds MPS3, the flange -temperature during head tensioning is assumed as the procedural minimum of 70--* degrees F, minus the temperature measurement uncertainty of 13 degrees F, or 57 degrees F. The flange temperature during head tensioning of 57 degrees F compared to the MPS2 RTndt of 10 degrees F, results in a margin of 47 degrees F. For a T-RTndt of 47 degrees, ASME Code Figure A-4200-1 provides a* K1c value of 86.3 ksi-'1inch. This material fracture toughness is conservatively adjusted by dividing by '110, similar to the allowable value used for normal operating temperatures. Denoting Kmax as the maximum K value for preload conditions from Table 2, the requested comparison becomes: Kmax < K1c from ASME Figure A-4200-1 '110 17.4 ksi-'1inch < 86.3 ksi-'1inch '110 17.4 ksi---Jinch < 27.3 ksi---Jinch Serial No.17-048 Docket Nos. 50-336/423 Attachment, Page 2 of 2 The comparison demonstrates that fracture toughness of the vessel flange materials during head tensioning is adequate to withstand the postulated flaws listed in Table 2.