2CAN032303, Responses to Request for Additional Information Concerning the Request for Alternative Regarding the Half-Nozzle Repair of Reactor Vessel Closure Head Penetration 46
| ML23088A198 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 03/29/2023 |
| From: | Couture P Entergy Nuclear Operations |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| 2CAN032303 | |
| Download: ML23088A198 (1) | |
Text
Entergy Operations, Inc., 1340 Echelon Parkway, Jackson, MS 39213 2CAN032303 10 CFR 50.55a March 29, 2023 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555
Subject:
Responses to Request for Additional Information Concerning The Request for Alternative Regarding the Half-Nozzle Repair of Reactor Vessel Closure Head Penetration #46 Arkansas Nuclear One, Unit 2 NRC Docket No. 50-368 Renewed Facility Operating License No. NPF-6 By letter dated January 20, 2023 (Reference 1), Entergy Operations, Inc. (Entergy) submitted a proposed alternative request in accordance with 10 CFR 50.55a(z)(1) for Arkansas Nuclear One, Unit 2 (ANO-2). The proposed alternative submittal includes the fracture mechanics evaluations of the triple point anomaly of the repair weld and the as-left flaw in the original J-groove weld to demonstrate the continued acceptability of previously repaired ANO-2 Reactor Vessel Closure Head Penetration Nozzle No. 46, through the remainder of the current renewed license (July 17, 2038). Entergy performed the nozzle repair, which had been authorized by the Nuclear Regulatory Commission (NRC) for one cycle of operation, during Refueling Outage 2R28 (Fall 2021) (Reference 2).
The NRC staff has reviewed the request and determined that additional information was required to complete their review (Reference 3).
The Request for Additional Information (RAI) and the associated responses are provided in the Enclosure.
There are no new regulatory commitments established in this submittal.
Phil Couture Senior Manager Fleet Regulatory Assurance - Licensing Tel 601-368-5102
2CAN032303 Page 2 of 2 If there are any questions or if additional information is needed, please contact Riley Keele, Manager, Regulatory Assurance, Arkansas Nuclear One, at 479-858-7826.
Respectfully, Phil Couture PC/rwc
Enclosure:
Responses to Request for Additional Information for Request for Alternative ANO2-RR-23-001
References:
- 1. Entergy Operations, Inc. (Entergy) letter to the U. S. Nuclear Regulatory Commission (NRC), " Relief Request ANO2-RR-23-001, Half-Nozzle Repair of Reactor Vessel Closure Head Penetration #46," (2CAN012302),
ML23020A941, dated January 20, 2023.
- 2. NRC letter to Entergy, "Arkansas Nuclear One, Unit 2 - Approval of Request for Alternative from Certain Requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (EPID L-2021-LLR-0084)," (2CNA042201), ML22073A095, dated April 7, 2022.
- 3. NRC email to Riley Keele (Entergy) "ANO-2 Final RAI RE: Alternative Request for Life-of-Repair of RVCH Pen. #46 (EPID L-2023-LLR-0000),"
(2CNA032301), dated March 10, 2023 cc:
NRC Region IV Regional Administrator NRC Senior Resident Inspector - Arkansas Nuclear One NRC Project Manager - Arkansas Nuclear One Philip Couture Digitally signed by Philip Couture Date: 2023.03.29 10:04:55 -05'00'
ENCLOSURE 2CAN032303 RESPONSES TO REQUEST FOR ADDITIONAL INFORMATION FOR REQUEST FOR ALTERNATIVE ANO2-RR-23-001
2CAN032303 Enclosure Page 1 of 3 RESPONSES TO REQUEST FOR ADDITIONAL INFORMATION FOR REQUEST FOR ALTERNATIVE ANO2-RR-23-001 By letter dated January 20, 2023 (Reference 1), Entergy Operations, Inc. (Entergy, licensee) submitted a proposed alternative request in accordance with 10 CFR 50.55a(z)(1) for Arkansas Nuclear One, Unit 2 (ANO-2). The proposed alternative submittal includes the fracture mechanics evaluations of the triple point anomaly of the repair weld and the as-left flaw in the original J-groove weld to demonstrate the continued acceptability of previously repaired ANO-2 Reactor Vessel Closure Head Penetration Nozzle No. 46, through the remainder of the current renewed license (July 17, 2038). Entergy performed the nozzle repair, which had been authorized by the Nuclear Regulatory Commission (NRC) for one cycle of operation, during Refueling Outage 2R28 (fall 2021) (Reference 2).
The NRC staff has reviewed the request and determined that additional information was required to complete their review (Reference 3).
Below is the Request for Additional Information (RAI) and the associated responses.
NRC REQUEST (RAI 1)
In the triple anomaly analysis, the licensee identified an analysis limitation regarding the minimum fluid temperature for certain transients (refer to nonpublic enclosure 1 of the letter dated January 20, 2023, Section 5.3, Item 5, Subitem a). In the as-left J-groove weld flaw evaluation, the licensee identified a similar analysis limitation regarding the minimum fluid temperature for certain transients (refer to nonpublic enclosure 1 of the letter, Section 5.4, Item 1 for analysis limitations). Clarify whether the licensee will control these transients during plant operation in such a manner to ensure that the actual transients meet these analysis limitations. If not, provide justification for why such control of the transients is not necessary, even though the analyses are based on the analysis limitations on the transients.
ENTERGYS RESPONSE (RAI 1)
There will be no new controls put in place for the analytical limitations as discussed in Reference 1. In regard to the Heat up and Cooldown transients, the current Low Temperature Overpressure Protection (LTOP) settings prevent the Reactor Coolant System (RCS) from ever reaching/exceeding these analytical limitations.
ANO-2 Technical Specification 3.4.12, "Low Temperature Overpressure Protection (LTOP),"
controls the settings. Limiting Condition for Operation 3.4.12.a requires the lift setpoint for the LTOP valves to be less than or equal to 430 psig. The Applicability of this TS is MODE 4 when the RCS cold leg temperature is less than or equal to 220 °F (including a 20 °F uncertainty),
MODE 5, and MODE 6 with reactor vessel head in place. When starting the first reactor coolant pump, the pressurizer water volume will be < 910 ft3. The LTOP enable temperature of 220 °F ensures the analytical limitations listed in Reference 1 are addressed. The peak mass addition LTOP transient pressure at the pressurizer location is 498.0 psia. The peak pressure at the pressurizer location for the limiting energy addition LTOP event is 497.5 psia. These peak pressures are less than the analytical limitation pressure listed in Reference 1.
2CAN032303 Enclosure Page 2 of 3 These settings are based on the Pressure-Temperature limits (ANO-2 TS 3.4.4.9) which are valid until 54 Effective Full Power Years (EFPY). The 54 EFPY time period will bound the operation of ANO-2 until the end of the current period of extended operation (i.e., 60 calendar years). Entergy has assumed that the unit would operate with an average capacity factor of 90% over this time period.
In regard to the Inservice Hydrostatic and Leak Test transients, although Entergy did include these transients in the analysis, it was later determined that these transients are not required to be considered for fatigue analysis (Reference 4).
NRC REQUEST (RAI 2)
In the triple anomaly analysis and as-left J-groove weld flaw evaluation, the licensee included weld residual stresses as part of the applied stresses. Provide a summary description of how the licensee estimated the weld residual stresses. In addition, if applicable, discuss any weld residual stress measurement data, other analysis results (e.g., benchmark results), or the conservatisms associated with the weld residual stress estimation that support the adequacy of the estimation.
ENTERGYS RESPONSE (RAI 2)
The weld residual stresses (WRS) used as part of the applied stresses in the triple anomaly analysis and as-left J-groove weld flaw evaluation were simulated using thermoplastic 3-dimensional finite element analysis. The finite element analyses consist of sequential thermal and structural analyses. Transient thermal analysis is performed first using multi-pass weld deposition with temperature dependent material properties and heat input to generate the temperature history in the welded components that is produced by the welding process. The temperature history from the thermal analysis is used as input to the multi-pass weld deposition in the subsequent structural analysis that predicts the residual stress distribution in the welded components. The structural analysis uses the time dependent multi-linear kinematic stress-strain relation for the simulated material. The finite element welding simulation procedure complies with the general recommendations of industry WRS modeling guidance documents such as MRP-317 (Reference 5). The various stages of the welding processes simulated by the 3-dimensional finite element model for the structural components include the buttering, J-groove weld, and the temper bead weld.
For WRS simulation validation purpose, Framatome (formerly known as AREVA NP Inc.)
participated in the finite element (FE) round robin study coordinated by the NRC and documented in NUREG-2228 (Reference 6). NUREG-2228 provided FE modeling guidance aimed at reducing analyst-to-analyst scatter. The round robin study involved modeling a pressurizer surge nozzle dissimilar metal weld as representative geometry. WRS measurements were also performed as documented in NUREG-2228. Participation in the NUREG-2228 round robin study demonstrated that the WRS prediction capability of Framatome's weld simulation procedure is consistent with other participants, and it provides assurance that the WRS simulation procedure follows the industry recommended practices.
2CAN032303 Enclosure Page 3 of 3 REFERENCES
- 1. Entergy Operations, Inc. (Entergy) letter to the U. S. Nuclear Regulatory Commission (NRC), " Relief Request ANO2-RR-23-001, Half-Nozzle Repair of Reactor Vessel Closure Head Penetration #46," (2CAN012302), ML23020A941, dated January 20, 2023.
- 2. NRC letter to Entergy, "Arkansas Nuclear One, Unit 2 - Approval of Request for Alternative from Certain Requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (EPID L-2021-LLR-0084)," (2CNA042201), ML22073A095, dated April 7, 2022.
- 3. NRC email to Riley Keele (Entergy) "ANO-2 Final RAI RE: Alternative Request for Life-of-Repair of RVCH Pen. #46 (EPID L-2023-LLR-0000)," (2CNA032301), dated March 10, 2023.
- 4. Entergy - CALC-86-E-0036-110, "Design Basis for ANO-2 Transients Used for Structural Design," Revision 0, Approved October 21, 2000.
- 5. Materials Reliability Program: Welding Residual Stress Dissimilar Metal Butt-Weld Finite Element Modeling Handbook (MRP-317, Revision 1). EPRI, Palo Alto, CA: 2015.
3002005499.
- 6. NUREG-2228, Weld Residual Stress Finite Element Analysis Validation Part IIProposed Validation Procedure, Final Report, ML20212L592, July 2020.