ML22038A187

Authorization and Safety Evaluation for Relief Request No. 19 (RR19) - the Use of an Alternative to ASME Code Case N-729-6 for Replacement Reactor Vessel Closure Head Penetration Nozzle 85

ML22038A187
Person / Time
Site:	Saint Lucie
Issue date:	02/09/2022
From:	David Wrona Plant Licensing Branch II
To:	Coffey B Florida Power & Light Co
Jordan, N.
References
EPID L-2021-LLR-0065
Download: ML22038A187 (4)

Text

February 9, 2022 ST. LUCIE NUCLEAR PLANT, UNIT NO. 2 - AUTHORIZATION AND SAFETY EVALUATION FOR RELIEF REQUEST NO. 19 (RR19) - THE USE OF AN ALTERNATIVE TO ASME CODE CASE N-729-6 FOR REPLACEMENT REACTOR VESSEL CLOSURE HEAD PENETRATION NOZZLE 85 (EPID L-2021-LLR-0065)

LICENSEE INFORMATION Recipients Name and Address: Mr. Bob Coffey Executive Vice President, Nuclear and Chief Nuclear Officer Florida Power & Light Company 700 Universe Blvd.

Mail Stop: EX/JB Juno Beach , FL 33408 Licensee: Florida Power and Light Plant Name(s) and Unit(s): St. Lucie Nuclear Plant, Unit 2 Docket No(s).: 50-389 APPLICATION INFORMATION Submittal Date: September 13, 2021 Submittal Agencywide Documents Access and Management System (ADAMS) Accession No.: ML21256A094 Alternative Provision: The licensee requested an alternative under Title 10 of the Code of Federal Regulations (10 CFR), paragraph 50.55a(z)(2)

ISI Requirement: 10 CFR 50.55a(g)(6)(ii)(D); Code Case N-729-6, Paragraphs -3142.2 and -3200 Applicable Code Edition and Addenda: The Fourth Ten Year ISI interval Code of record for St. Lucie Nuclear Plant (St. Lucie) Unit 2 is the 2007 Edition with 2008 Addenda of American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code),Section XI, which ends on August 8, 2023.

Brief Description of the Proposed Alternative: The licensee is requesting relief from ASME Code Case N-729-6 paragraphs -3142.2 & -3200 for performing volumetric and/or surface exams of the St. Lucie Unit 2 Reactor Vessel Closure Head (RVCH) penetration 85. As an alternative, the licensee proposes to perform a bare metal visual examination (VE) of penetration 85 at the next refueling outage after cleaning and documentation of the as left condition (SL2 Spring 2023).

For additional details on the licensees request, please refer to the documents located at the ADAMS Accession No(s) identified above.

STAFF EVALUATION The NRC verbally authorized the licensees proposed alternative on September 14, 2021, for St. Lucie Nuclear Plant, Unit 2 (ADAMS Accession No. ML21258A101). The following provides the documented staff evaluation of the licensees proposed alternative.

The licensee requested authorization for this alternative in accordance with the requirements of 10 CFR 50.55a(z)(2), on the basis that performing the supplemental examinations represents a hardship or unusual difficulty without a compensating increase in the level of quality and safety.

In performance of the current refueling outage bare metal VE of the RVCH, the licensee found a relevant condition on the head surface near RVCH penetration number 85. After light cleaning and evaluation, the licensee took several actions to identify the source of the leakage and confirm it was not active pressure boundary leakage by isotopic analysis. However, the licensee was not able to conclusively identify the source of the leakage. Therefore, the licensee considered the indication on the head surface to be relevant condition of possible nozzle leakage in accordance with Paragraph -3142.1 of ASME Code Case N-729-6. Under these provisions, the licensee is required to perform either a repair/replacement activity or supplemental volumetric examinations in accordance with Paragraph -3200(b) of ASME Code Case N-729-6. Instead of the supplemental volumetric examinations, the licensee stated that it would clean the remaining area of the RVCH surface and verify the structural integrity of the RVCH. During the upcoming cycle of operation, the licensee stated that it would monitor for leakage in a manner which will continue to ensure the structural integrity of the RVCH. Finally, at the end of the current operating cycle 26, the licensee would perform an additional bare metal VE of the RVCH near penetration 85 to ensure no leakage is occurring.

The U. S. Nuclear Regulatory Commission (NRC) staff reviewed the licensees identified hardship and found the licensees estimation of radiological dose to perform the supplemental volumetric examinations during this outage was consistent with estimates at other facilities. The NRC staff finds that the radiological dose estimate of 7.5 person-REM for this work is a hardship on the licensee consistent with 10 CFR 50.55a(z)(2).

The NRC notes that the nozzle and weld material (alloy 690/52/152) of the RVCH at St. Lucie, Unit 2 has demonstrated no cracking in service in pressurized water reactor environments, which supports the conclusion that it is unlikely that cracking is currently present. Further, even if minor leakage of a RVCH penetration was currently occurring, the known resistance of alloy 690/52/152 to crack growth provides additional assurance that any cracking currently present would be unlikely to increase to the point of challenging the structural integrity of the RVCH over one additional operating cycle. This analysis is supported by NRC sponsored alloy 690/52/152 crack growth rate and initiation testing at Argonne National Laboratory (ANL) and Pacific Northwest National Laboratory (PNNL) with latest reports under PNNL Final NUREG/CR:

Pacific Northwest National Laboratory Investigation of Stress Corrosion Cracking in Nickel-Base Alloys: Dissimilar Metal Interface Regions and Assessment of Program Results, NUREG/CR-7103, Volume 5, and ANL 2018 NUREG/CR: Primary Water Stress Corrosion Cracking of High-Chromium Nickel-Base Welds - 2018, NUREG/CR-7276. Finally, the licensees identified leakage monitoring actions enable detection of the onset of, or increase in, leakage through a RVCH penetration prior to it presenting a challenge to structural integrity of the RVCH. Hence, the NRC finds that the licensees proposed alternative provides reasonable assurance of the structural integrity of the RVCH for the next operating cycle at St. Lucie, Unit 2

without requiring the licensee to perform supplemental volumetric examinations during the current refueling outage.

Therefore, the NRC staff finds, given the actions of the licensees proposed alternative, under Relief Request Number 19, there would be limited value in quality and safety in requiring additional supplemental volumetric examinations to verify no indications of cracking in these materials during the current refueling outage. Given the hardship, the NRC staff finds that (1) there is reasonable assurance that the licensees proposed alternative has a minimal impact on quality and safety; and (2) the licensees hardship justification is acceptable.

CONCLUSION The NRC staff has determined that complying with the specified 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 RVCH and penetration nozzle 85 for the next operating cycle 26 at St. Lucie Unit 2. 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 alternative Relief Request Number 19 at St. Lucie Nuclear Plant, Unit 2, until the end of operating cycle 26, which is scheduled to end in Spring 2023.

All other ASME BPV 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(s): J. Collins, NRR/DNRL Date: February 9, 2022 Digitally signed by David J. David J. Wrona Date: 2022.02.09 Wrona 10:28:15 -05'00' David J. Wrona, Chief Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation cc: Listserv

ML22038A187 *By Memo OFFICE NRR/DORL/LPL2-2/PM NRR/DORL/LPL2-2/LA NRR/DNRL/NPHP/BC(A)*

NAME NJordan RButler SCumblidge DATE 2/2/2022 2/7/2022 1/28/2022 OFFICE NRR/DORL/LPL2-2/BC NRR/DORL/LPL2-2/PM NAME DWrona NJordan DATE 2/9/2022 2/9/2022