RS-25-033, Response to NRC Request for Additional Information, Set 1, Dated January 10, 2025 Related to License Renewal Application
| ML25050A041 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 02/19/2025 |
| From: | Wilson C Constellation Energy Generation |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| RS-25-033 | |
| Download: ML25050A041 (1) | |
Text
200 Energy Way Kennett Square, PA 19348 www.ConstellationEnergy.com RS-25-033 10 CFR 50 10 CFR 51 10 CFR 54 February 19, 2025 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Clinton Power Station, Unit 1 Facility Operating License No. NPF-62 NRC Docket No. 50-461
Subject:
Response to NRC Request for Additional Information, Set 1, dated January 10, 2025 related to the Clinton Power Station, Unit 1, License Renewal Application
References:
- 1. Letter from Christopher D. Wilson (Constellation Energy Generation, LLC) to U.S. NRC, Application for Renewed Operating License, dated February 14, 2024 (ML24045A024)
- 2. E-mail from Christopher Tyree (U.S. NRC) to Christopher D. Wilson (Constellation Energy Generation, LLC), dated January 10, 2025, Clinton LRA - Requests for Additional Information - Set 1 (ML25010A350)
- 3. Letter from Christopher D. Wilson (Constellation Energy Generation, LLC) to U.S. NRC, Response to NRC Requests for Additional Information and Request for Confirmation of Information, Set 1, dated January 10, 2025 related to the Clinton Power Station, Unit 1, License Renewal Application, dated January 30, 2025 (ML25030A189)
In Reference 1, Constellation Energy Generation, LLC (CEG) submitted a License Renewal Application (LRA) for Clinton Power Station, Unit 1 (CPS). In Reference 2, the NRC requested additional information and confirmation of information to support staff review of the LRA. As indicated in Reference 2, the schedule for responding to the requests for additional information (RAI) and the request for confirmation of information (RCI) is within 30 days from the date of the email with the exception of RAI 4.3.2-3 which is due within 45 days from the date of the email.
The responses due within 30 days were provided in Reference 3.
Enclosure A provides the response to RAI 4.3.2-3.
There are no new regulatory commitments contained in this letter.
Should you have any questions regarding this submittal, please contact Ms. Lydia S.
Dworakowski, Licensing Lead, CPS License Renewal Project, by email at Lydia.Dworakowski@constellation.com.
Constellation
February 19, 2025 U.S. Nuclear Regulatory Commission Page 2 I declare under penalty of perjury that the foregoing is true and correct. Executed on the 19th day of February 2025.
Respectfully, Christopher D. Wilson License Renewal Director Constellation Energy Generation, LLC
Enclosure:
A. Response to Request for Additional Information cc:
NRC Regional Administrator, Region III NRC Senior Resident Inspector - Clinton Power Station NRC Project Manager (Safety Review), NRR-DNRL NRC Project Manager (Environmental Review), NRR-DNRL NRC Project Manager, NRR-DORL - Clinton Power Station Illinois Emergency Management Agency - Division of Nuclear Safety Wilson, Christopher D Digitally signed by Wilson, Christopher D Date: 2025.02.19 08:40:33 -05'00'
Enclosure A Response to Request for Additional Information Clinton Power Station, Unit 1 License Renewal Application (LRA)
RAI 4.3.2-3
February 19, 2025 Enclosure A Page 1 of 3 RAI 4.3.2-3 Regulatory Basis Pursuant to 10 CFR 54.21(c), the LRA must include an evaluation of time-limited aging analyses (TLAAs). The applicant must demonstrate that (i) the analyses remain valid for the period of extended operation, (ii) the analyses have been projected to the end of the period of extended operation, or (iii) the effects of aging on the intended function(s) will be adequately managed for the period of extended operation.
=
Background===
LRA Section 4.3.2.2 addresses the environmentally assisted fatigue analysis (EAF).
Specifically, the following report describes the EAF analysis for limiting locations (
Reference:
Structural Integrity Associates (SIA) 1701003.305, Environmentally Assisted Fatigue Calculations for Sentinel Locations at Clinton, March 17, 2023). The report indicates that the calculation of the environmental fatigue correction factor (Fen) uses the average temperature of a transient.
Issue NUREG/CR-6909, Revision 1, Section 4.1.4 and related discussions explain that the average temperature of a transient may be used in the Fen calculation for a simple, linear transient.
NUREG/CR-6909, Revision 1 also indicates that, if a transient is complex, justification is needed to use an average temperature rather than the maximum temperature. However, the LRA does not clearly discuss the basis for the use of the average temperature approach.
Request Clarify whether the applicants use of an average temperature is only for simple, linear transients. If not, provide the following information: (1) justification for the average temperature approach and (2) plant-specific demonstration that the conservatism of the applicants approach is comparable to that of the modified rate approach described in NUREG/CR-6909, Revision 1, Section 4.4 in terms of calculating the Fen and environmentally adjusted cumulative usage factor (CUFen).
Constellation Response (1) This question is related to the detailed EAF analyses which support the projected 60-year CUFen values in LRA Table 4.3.1-2.
NUREG/CR-6909 Revision 1, Section 4.1.4 states:
For simple, linear transients, an average temperature that considers the threshold temperature of 150°C may be used to calculate Fen for a specific stress cycle or load set pair. Complex thermal transients that have multiple increasing and decreasing temperature excursions should be evaluated using the maximum temperature for the specific stress cycle or load set pair unless information is available to justify the use of an average temperature.
February 19, 2025 Enclosure A Page 2 of 3 Based on this guidance, it is concluded that all but a few of the transients assumed in the detailed EAF analysis are simple linear transients which do not have multiple increasing and decreasing temperature excursions. For these simple transients, the detailed EAF analysis uses the average temperature of these transients to determine the Fen value for specific stress cycles or load pairs.
However, a few of the transients assumed in the detailed EAF analysis are not simple linear transients as described in NUREG/CR-6909 Revision 1. These are transients 10, 11, 20, and 22 in LRA Table 4.3.1-1. Because multiple increasing and decreasing temperature excursions can result in multiple stress peaks and valleys, these complex transients are generally split up in the detailed fatigue analysis, so all the stress peaks and valleys are captured. This effectively turns a complex transient into multiple simple transients for EAF analysis. NUREG/CR-6909 Revision 1, Section 4.1.4 does allow the use of average temperatures for transients that are not simple linear transients if information is available that justifies the use of this approach.
Industry information is available that justifies the use of the average temperature approach for transients that are not simple in a paper entitled Use of Average Temperature in Fen Calculations, Proceedings of the ASME 2020 Pressure Vessel & Piping Conference, PVP2020-21009. This paper compares Fen values based on the modified rate approach with those using the average temperature approach. The paper documents case studies where the modified rate approach and average temperature approach are used on various BWR and PWR reactor pressure vessel components of varying materials. The paper concluded that in every case study, the total CUFen value was greater (more conservative) with a Fen value based on the average temperature approach rather than a Fen value based on the modified rate approach.
(2) To provide additional confirmation that the use of the average temperature approach is comparable for complex thermal transients, as opposed to the modified rate approach, an actual transient associated with the AB feedwater nozzle was evaluated (item number 40 in LRA Table 4.3.1-2). The transient occurred at Clinton during a reactor scram due to a turbine trip (transient 10 in LRA Table 4.3.1-1) on January 31, 2023. This transient is considered a complex thermal transient since the nozzle experienced at least two decreasing temperature excursions and at least one increasing temperature excursion.
At Clinton, the FatigueProTM software monitors the feedwater nozzles (items 38 through 41 in LRA Table 4.3.1-2) using stress based fatigue monitoring methodology. After a transient occurs, FatigueProTM calculates Fen values for these feedwater nozzle components based on the modified rate approach.
For comparison, the Fen value was also calculated using the average temperature value in accordance with the guidance in NUREG/CR-6909 Revision 1 Appendix A, using equation A-8 on page A-2. An input value of 0.29 for the O* value was used to bound all SS materials. The minimum strain rate of 0.0004 (%/sec) is used in all cases, which is conservative because it results in larger Fen values.
The temperature profile of the January 31, 2023 transient is provided in Figure 1 and the Fen results based on the two methodologies are presented in Table 1 below.
February 19, 2025 Enclosure A Page 3 of 3 Table 1 - Results Date Calculated FatigueProTM Fen Value Based on Modified Rate Approach Tmax Tmin Tave Calculated Fen Value Based on Average Temperature Approach January 31, 2023 1.7 530°F 212°F(1) 371°F 2.7 Note 1: For the minimum temperature, the threshold temperature for stainless steel was used instead of the actual temperature as recommended in NUREG/CR-6909 Revision 1.
The Fen value calculated using the average temperature approach is conservative with respect to the Fen value calculated by FatigueProTM using the modified rate approach. This plant specific demonstration provides additional confirmation that the average temperature approach is not only comparable but also conservative when calculating the Fen value and environmentally adjusted cumulative usage factor (CUFen) for complex thermal transients at Clinton.
~
GRW:1 X
0 Read Only IR oc:TNOZA8 a,-ioc:Treactorl 600~-----~-----~ ------~-----~-----~-----~
t
~
E 300t------+-------+------'l~
1--t------+-----111'----+-~ '-------------t t e
~
01/ 31/ 23 02/01/23 02/02/23 02/03/ 23 02/04/ 23 02/05/23 Dote/Time (1/ 31/23.. 2/04/23]
l !;raph~ions... l Figure 1: 1/31/2023 to 2/4/2023 Temperature Data