ML23255A286

NRR E-mail Capture - South Texas Project Draft Request for Additional Information License Amendment Request to Revise the Alternate Source Term Dose Calculation (L-2023-LLA-0047)

ML23255A286
Person / Time
Site:	South Texas, 07201041
Issue date:	09/12/2023
From:	Dennis Galvin NRC/NRR/DORL/LPL4
To:	Brost W South Texas
References
L-2023-LLA-0047
Download: ML23255A286 (4)

Text

From: Dennis Galvin Sent: Tuesday, September 12, 2023 9:40 AM To: Wendy Brost (webrost@stpegs.com)

Cc: Tim Hammons (tjhammons@stpegs.com)

Subject:

South Texas Project - Draft Request for Additional Information - License Amendment Request to Revise the Alternate Source Term Dose Calculation (L-2023-LLA-0047)

Attachments: STP LAR to Revise Alternative Source Term Dose Calc - Draft RAI Issued 2023-09-12.pdf

Dear Ms. Brost,

By letter dated March 30, 2023 (ADAMS Accession No. ML23089A204), the STP Nuclear Operating Company submitted a license amendment request for South Texas Project Units 1 and 2 to the U.S. Nuclear Regulatory Commission (NRC). The proposed amendments would authorize revision of the alternate source term dose calculation for the main steam line break (MSLB) and the locked rotor accident (LRA). The reanalysis uses the asymmetric natural circulation cooldown thermohydraulic analyses, various radiation transport assumptions, and the current licensing basis source term and meteorological data to evaluate the dose effects of an extended cooldown on the existing accident analyses.

To complete its review, the NRC staff has prepared a request for additional information (RAI) in DRAFT form. To arrange a clarification call for the draft RAIs and to discuss the due date for the RAI response, please contact me at (301) 415-6256.

Respectfully, Dennis Galvin Project Manager U.S Nuclear Regulatory Commission Office of Nuclear Reactor Regulation Division of Operating Reactor Licensing Licensing Project Branch 4 301-415-6256 Docket Nos. 50-498, 50-499

Hearing Identifier: NRR_DRMA Email Number: 2232 Mail Envelope Properties (SA1PR09MB811101A067961968A7CDC6E6FBF1A)

Subject:

South Texas Project - Draft Request for Additional Information - License Amendment Request to Revise the Alternate Source Term Dose Calculation (L-2023-LLA-0047)

Sent Date: 9/12/2023 9:39:35 AM Received Date: 9/12/2023 9:39:00 AM From: Dennis Galvin Created By: Dennis.Galvin@nrc.gov Recipients:

"Tim Hammons (tjhammons@stpegs.com)" <tjhammons@stpegs.com>

Tracking Status: None "Wendy Brost (webrost@stpegs.com)" <webrost@stpegs.com>

Tracking Status: None Post Office: SA1PR09MB8111.namprd09.prod.outlook.com Files Size Date & Time MESSAGE 1200 9/12/2023 9:39:00 AM STP LAR to Revise Alternative Source Term Dose Calc - Draft RAI Issued 2023-09-12.pdf 191989 Options Priority: Normal Return Notification: No Reply Requested: No Sensitivity: Normal Expiration Date:

DRAFT REQUEST FOR ADDITIONAL INFORMATION LICENSE AMENDMENT REQUEST STP NUCLEAR OPERATING COMPANY SOUTH TEXAS PROJECT, UNITS 1 AND 2 DOCKET NOS. 50-498 AND 50-499 By letter dated March 30, 2023 (ADAMS Accession No. ML23089A204), the STP Nuclear Operating Company (STPNOC, the licensee) submitted a license amendment request (LAR) for South Texas Project (STP), Units 1 and 2 to the U.S. Nuclear Regulatory Commission (NRC).

The proposed amendments would authorize revision of the alternate source term dose calculation for the main steam line break (MSLB) and the locked rotor accident (LRA). The reanalysis uses the asymmetric natural circulation cooldown thermohydraulic analyses, various radiation transport assumptions, and the current licensing basis source term and meteorological data to evaluate the dose effects of an extended cooldown on the existing accident analyses.

Based on a review of the proposed MSLB and LRA asymmetric natural circulation cooldown (ANCC) analysis in Sections 3.2.1 and 3.3.1 of the LAR enclosure, respectively, the NRC staff has identified the following requests for additional information (RAIs).

SNSB-RAI 1 Regulatory Basis 10 CFR 50, Appendix A, GDC 10, as it relates to the reactor coolant system (RCS) being designed with appropriate margin to ensure that the specified acceptable fuel design limits are not exceeded during normal operations including anticipated operational occurrences.

RAI Section 2.3 of the LAR enclosure states:

The MSLB and LRA events are impacted by this change because these events and the assumptions imposed by the analysis require cooling down an intact RCS without all four steam generators during a coincident LOOP [loss-of-offsite power]. Other accidents such as LOCA [loss-of-coolant accident], Steam Generator Tube Rupture, and Rod Ejection all involve some type of break in the RCS, their cooldown timeline is not impacted and they are not re-analyzed.

(a) The LAR indicates that if one or more steam generators were not available for RCS cooldown, an ANCC issue that resulted in a stagnant loop conditions would have an impact on both the thermal-hydraulic analysis and the dose analysis. Sections 3.2.1 and 3.3.1 present assumptions to be used in updated MSLB and LRA ANCC RETRAN analyses, respectively, but the LAR does not explain why these assumptions are suitably conservative or what controls will be put in place to implement these assumptions. For example, a cooldown rate of 15oF/hr is assumed to prevent stagnation. However, the LAR does not explain why a higher or lower cool down rate or permitting stagnation would not be more

conservative, or if controls are in place such that other assumptions do not need to be considered. Explain how the proposed assumptions are suitably conservative or are otherwise appropriate.

(b) LAR Section 2.3 indicates that the non-LOCA events described in Updated Final Safety Analysis Report Sections 15.1 through 15.6, other than MSLB and LRA, are not impacted by the ANCC condition resulting from inactive steam generator(s) caused by the assumed limiting single failure in their analysis without providing a justification. Provide justifications that the other events are not impacted by the ANCC condition.

SNSB-RAI 2 Regulatory Basis:

10 CFR 50, Appendix A, GDC 10, as it relates to the RCS [reactor coolant system] being designed with appropriate margin to ensure that the specified acceptable fuel design limits are not exceeded during normal operations including anticipated operational occurrences.

RAI Sections 3.2.1 and 3.3.1 of the LAR enclosure provide assumptions used in the proposed MSLB and LRA ANCC analysis, respectively. Identify if there are any differences in assumptions and the RETRAN inputs. For the differences (if any), provide justification in case the conservatism is reduced.