ML20143A077
| ML20143A077 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 05/26/2020 |
| From: | Dominion Energy Nuclear Connecticut |
| To: | NRC/NRR/DORL/LPL1 |
| Guzman R | |
| References | |
| EPID L-2020-LRM-0040) | |
| Download: ML20143A077 (9) | |
Text
Millstone Power Station Unit 2 (MPS2)
Inspection Interval Extension Alternative Request for Steam Generator Pressure Retaining Welds and Full Penetration Welded Nozzles NRC Pre-Submittal Meeting May 26, 2020 May 26, 2020 1
- Dominion Energy Nuclear Connecticut, Inc. (DENC) will be requesting approval of an alternative request for MPS2 to increase the inspection interval for steam generator Class 1 and 2 pressure-retaining welds and full penetration welded nozzles
- Key Goals for This Meeting:
Brief NRC on proposed alternative request, supporting information, and proposed timeline Discuss the request prior to formal submittal Ensure common understanding of the MPS2 request, technical scope and regulatory expectations Meeting Objectives May 26, 2020 2
- Steam generator Class 1 and 2 pressure-retaining welds and full penetration welded nozzles (2 loop CE unit)
- ASME Section XI IWB-2500(a), Table IWB-2500-1 and IWC-2500(a), Table IWC-2500-1 Affected Components May 26, 2020 3
ASME Category Item No.
Description B-B B2.31 Steam generators (primary side), head welds, circumferential B-B B2.40 Steam generators (primary side), tubesheet-to-head weld B-D B3.130 Steam generators (primary side), nozzle-to-vessel welds C-A C1.10 Shell circumferential welds C-A C1.20 Head circumferential welds C-A C1.30 Tubesheet-to-shell weld C-B C2.21 Nozzle-to-shell (nozzle to head or nozzle to nozzle) welds C-B C2.22 Nozzle inside radius sections
- Increase the inspection interval for these examination items to 30 years (from the current ASME Code Section XI 10-year requirement) for the remainder of the fifth and through the following sixth 10-year inspection interval o
The duration of the proposed alternative would end on March 31, 2040, pending MPS2 subsequent license renewal beyond July 31, 2035
- Proposed alternative will demonstrate an acceptable level of quality and safety in accordance with 10 CFR 50.55a(z)(1)
Proposed Alternative May 26, 2020 4
EPRI Report 3002015906, Technical Bases for Inspection Requirements for PWR Steam Generator Class 1 Nozzle-to-Vessel Welds and Class 1 and Class 2 Vessel Head, Shell, Tubesheet-to-Head and Tubesheet-to-Shell Welds, October 2019 (publicly available)
Applicable to Category B-B, B-D, and C-A items EPRI Report 3002014590, Technical Bases for Inspection requirements for PWR Steam Generator Feedwater and Main Steam Nozzle-to-Shell Welds and Inside Radius Sections, April 2019 (publicly available)
Applicable to Category C-B items No approved precedents for this type of request at present A similar alternative request is currently under review for Vogtle 1 and 2 (ML19347B105) - for examination category C-B components (using EPRI Report 3002014590) only Basis for Request & Precedent May 26, 2020 5
The EPRI reports provide the following technical justification:
Industry examination history and previous industry initiatives have optimized examination requirements for similar components Degradation mechanism, probabilistic fracture mechanics (PFM), and deterministic fracture mechanics (DFM) evaluations for these welds and nozzles conclude that no other inspections are required until 80 years to meet the NRC safety goal of 10-6 failures per reactor year All welds and components considered in these reports are very flaw-tolerant The probabilistic fracture mechanics software used to compile the EPRI reports is consistent with the PFM White Paper provided by EPRI to the NRC Technical Justification May 26, 2020 6
- MPS2 request will demonstrate that plant specific configurations and operating conditions are bounded by the criteria of the EPRI technical justification reports
- MPS2 inspection history shows that no flaws exceeding the ASME Section XI acceptance standards were identified during any examinations
Conclusion:
ASME Section XI inspection schedules can be optimized (to at least 30 years) while continuing to provide an acceptable level of quality and safety Applicability & Inspection History May 26, 2020 7
- Submittal of alternative request to the NRC expected by end of June 2020
- NRC approval requested by no later than August 1, 2021, to support the fall 2021 MPS2 refueling outage Schedule May 26, 2020 8
Questions?
May 26, 2020 9