ML21284A006

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Authorization and Safety Evaluation for Alternative Request No. RR-05-04 and IR-4-02
ML21284A006
Person / Time
Site: Millstone  Dominion icon.png
Issue date: 10/29/2021
From: James Danna
NRC/NRR/DORL/LPL1
To: Stoddard D
Dominion Energy Nuclear Connecticut
Guzman R
References
EPID L-2020-LLR-0158
Download: ML21284A006 (6)


Text

MILLSTONE POWER STATION, UNIT NOS. 2 AND 3 - AUTHORIZATION AND SAFETY EVALUATION FOR ALTERNATIVE REQUEST NO. RR-05-04 AND IR-4-02 (EPID L-2020-LLR-0158)

LICENSEE INFORMATION Recipients Name and Address: Mr. Daniel G. Stoddard Senior Vice President and Chief Nuclear Officer Dominion Energy Nuclear Connecticut, Inc.

Millstone Power Station Innsbrook Technical Center 5000 Dominion Blvd.

Glen Allen, VA 23060-6711 Licensee:

Dominion Energy Nuclear Connecticut, Inc.

Plant Name and Units:

Millstone Power Station, Unit Nos. 2 and 3 Docket Nos.:

50-336 and 50-423 APPLICATION INFORMATION Application Date: December 17, 2020 Application Agencywide Documents Access and Management System (ADAMS)

Accession No.: ML20352A334 Supplement Date: N/A Applicable Inservice Inspection (ISI) Program Interval and Interval Start/End Dates: For RR-05-04, the alternative is requested for the fifth 10-year ISI interval for Millstone Power Station, Unit No. 2 (MPS2). The MPS2 fifth 10-year ISI interval began April 1, 2020, and is currently scheduled to end on March 31, 2030. For IR-4-02, the alternative is requested for the fourth ten-year ISI interval for Millstone Power Station, Unit No. 3 (MPS3). The MPS4 fourth 10-year ISI interval began February 23, 2019, and is currently scheduled to end on February 22, 2029.

Alternative Provision: The applicant requested an alternative under Title 10 of the Code of Federal Regulations (10 CFR), paragraph 50.55a(z)(2).

ISI Requirements: Section XI, Table IWD-2500-1, Examination Category D-B and IWD-5220 require Class 3 piping receive a system leakage test at the pressure obtained while the system is performing its normal function and a VT-2 visual examination once per inspection period.

Applicable Code Edition and Addenda: 2013 Edition of the American Society of Mechanical Engineers (ASME) Code,Section XI.

ASME Code Components Affected:

Unit 2 MPS2s Service Water System (SWS) supply piping located in the intake structure bays designated as line numbers 24-JGD-1 and 24-KE-1 as shown in the December 17, 2020, submittal.

Unit 3 MPS3s 30 SWS supply piping located in the intake structure bays designated as B train line number 3-SWP-030-3-3 as shown in the December 17, 2020, submittal.

Brief Description of the Proposed Alternative:

The licensee proposes to use a verification of unimpaired flow performed during quarterly SWS flow testing along with internal visual inspection of the piping to be performed every other refueling outage in lieu of the ASME Code-required system leakage test and VT-2 examination for the subject piping. The licensee requested the use of these alternatives for the duration of the MPS2s fifth and MPS3s fourth ten-year interval.

For additional details on the licensees request, please refer to the documents located at the ADAMS Accession Nos. identified above.

STAFF EVALUATION The NRC staff has evaluated Alternative Requests RR-05-04 and IR-4-02 pursuant to 10 CFR 50.55a(z)(2). Specifically, the U.S. Nuclear Regulatory Commission (NRC) staff has reviewed the affected pipe segments, flow test procedures, and internal visual examinations to determine if the alternatives provide reasonable assurance of structural integrity. The NRC staff also reviewed whether complying with the specified requirement would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

Affected Piping Segments Unit 2 The subject piping is the 24 SWS train A and B supply piping located in normally inaccessible confined space areas of the intake structure bays. The nominal wall thickness of the 24"-JGD-1 piping is 0.375 inches. The nominal wall thickness of the 24"-KE-1 piping is 0.410 inches. The normal operating pressure is 45 pounds per square inch gauge (psig). The normal operating temperature range is 33 °F to 80 °F.

The A train piping includes approximately 75 feet of piping running through four intake structure bays. The majority of this piping is A-106, Grade B carbon steel piping which has been internally lined with a cured in-place pipe, epoxy-impregnated material (lnsituform), and externally coated with an epoxy coal tar material (Carbomastic 14), in order to enhance its long-term life. Approximately 10.5 feet of this piping has been upgraded to 6 percent molybdenum stainless steel (UNS N08367), also known as AL6XN.

The B train piping consists of approximately 22 feet of piping running through one intake structure bay. This piping has been upgraded to AL6XN.

The VT-2 visual examination of this piping requires entry into each of the four MPS2 intake structure bays (A, B, C, and D) that are designated as confined spaces.

Unit 3 The subject piping is the 30 common B train SWS header piping located in the normally inaccessible confined space areas of the MPS3 intake structure bays. The nominal wall thickness of the subject piping is 0.375 inches. The normal operating pressure is 44 psig. The normal operating temperature range is 33 °F to 80 °F. The piping material is SB-127 (Monel).

The inaccessible piping consists of approximately 99 feet of piping running through the five MPS3 intake structure bays. The licensee stated that no repairs or upgrades to this piping section have been performed and the service history of this piping has shown no significant degradation.

The staff notes the required VT-2 visual examinations would continue to be performed on the remaining accessible portions of the MPS2 and MPS3 SWS piping not covered by this alternative request, when conducting the system leakage test in accordance with ASME Code,Section XI, IWD-5000 and IWA-5244(b)(2) for buried components.

Additionally, the intake structure is walked down once per shift during plant equipment operator rounds. Any significant leakage in the inaccessible piping would likely be audible to the operators during these rounds.

Flow Test Procedures The flow testing of the MPS2 and MPS3 SWS pumps is performed quarterly and uses an established minimum flow rate specified in the IST procedures as the acceptance criteria for the pressure testing of the subject piping segments. Once the reference flow rate is established, pump performance parameters are recorded (e.g., suction pressure, discharge pressure, and flow). If the flow rate cannot be achieved or the associated differential pressure at the reference conditions is not achieved, the test is considered to be unsatisfactory. The Corrective Action Program (CAP) would be used to determine the cause and return the pumps to operable status.

The CAP would initiate additional activities, such as pump maintenance and additional system walkdowns/inspections, to determine the cause of the issue. If during the investigation it is suspected that there may be leakage occurring from the subject piping addressed by this request, actions would be taken to gain access to this normally inaccessible piping for visual inspection, as necessary.

The NRC staff finds that the licensee's flow testing program is adequate to determine potential through wall leakage from the affected pipe segments because the licensee's CAP contains procedures requiring corrective actions to be performed to determine the source of the leakage, regardless of the source. Additionally, the plant equipment operator performs walkdowns of accessible areas of the intake structure once each shift. Any significant flow from leakage of the subject piping would likely be audible to the operator during these rounds. Therefore, the NRC staff finds that the licensee will properly identify the pipe through wall leakage, if it occurred, and take corrective actions in accordance with its CAP.

Piping Internal Inspections The licensee stated that each of the subject piping segments inside surface is visually inspected using a robotic crawler at an approximately 3-year frequency. The robotic crawler is fitted with a high-resolution camera. The licensee stated that any identified conditions such as erosion corrosion, fouling or any other degraded piping conditions are evaluated for acceptance or corrective action. Inspections performed over the last two MPS2 and MPS3 refueling outages have identified no unsatisfactory conditions.

The NRC staff notes that the 3-year frequency for performing the internal visual inspection is essentially equivalent to the timing of the ASME Code-required system leakage test and, therefore, is acceptable. The NRC staff finds that, in addition to the flow test, the periodic internal visual inspection will provide additional assurance on the structural integrity of the affected piping.

Hardship Justification In the December 17, 2020, submittal, the licensee described that personnel entry into the confined space of the intake bays with equipment operational is considered a personnel safety hazard. Therefore, equipment is required to be removed from service and tagged out prior to entry. Additionally, due to the physical configuration of the intake structure, seven of the nine bays require draining to erect the scaffolding needed to access these bays. Draining the bays also requires equipment to be removed from service to preclude damage to the service water pumps that could occur with the bays drained. The licensee explained that unavailability of safety-related service water pumps places the station at a greater operational risk since it removes the availability of redundant equipment, introducing a reduction in the safety margin of the plant. Placing the plant in a condition where safety-related service water is out of service for an extended period of time, resulting in increased operational risk, is considered a hardship without a compensating increase in the level of quality and safety.

The NRC staff finds that the licensee has provided valid arguments to demonstrate that complying with the specified ASME Code requirement would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

Based on information provided, the NRC staff finds that the proposed alternatives RR-05-04 and IR-4-02 will provide reasonable assurance of the structural integrity and leak tightness of the affected SWS piping segments because: (1) the flow test procedures will be able to detect potential leakage in the affected pipe segments in the intake structure bays; (2) the licensee performs visual examinations on the inside surface of the affected pipe segments approximately every three years which would detect potential pipe degradation; and (3) the plant operator walkdowns of the accessible areas of the intake structure during every shift which will identify significant leakage in the inaccessible areas. The NRC staff also finds the licensees hardship justification is acceptable and that complying with the specified ASME Code requirement would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

CONCLUSION The NRC staff has determined that complying with the specified ASME Code requirements described in the licensees request referenced above would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

The proposed alternative provides reasonable assurance of structural integrity of the subject piping segments.

The NRC staff concludes that the licensee has adequately addressed the regulatory requirements set forth in 10 CFR 50.55a(z)(2).

The NRC staff authorizes the use of proposed alternatives RR-05-04 and IR-4-02 at Millstone Power Station, Units 2 and 3, for the fifth and fourth 10-year intervals, respectively.

All other ASME Code,Section XI, requirements for which an alternative was not specifically requested and authorized remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.

Principal Contributor: Keith Hoffman Date: October 29, 2021 James G. Danna, Chief Plant Licensing Branch I Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation cc: Listserv James G.

Danna Digitally signed by James G. Danna Date: 2021.10.29 13:45:20 -04'00'

ML21284A006 OFFICE NRR/DORL/LPL1/PM NRR/DO - L/LPL1/LA NRR/DNRL/NPHP/BC NAME RGuzman KEntz MMitchell DATE 10/13/2021 10/12/2021 8/9/2021 OFFICE NRR/DORL/LPL1/PM NAME JDanna DATE 10/29/2021