ML26076A179
| ML26076A179 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  (NPF-072, NPF-077) |
| Issue date: | 03/17/2026 |
| From: | Scott Wall NRC/NRR/DORL/LPL3 |
| To: | Seawright B Constellation Energy Generation |
| Wall, S | |
| References | |
| EPID L-2024-LLA-0172 | |
| Download: ML26076A179 (0) | |
Text
From:
Scott Wall To:
Seawright, Brian A: (Constellation Nuclear)
Cc:
Steinman, Rebecca L:(Constellation Nuclear)
Subject:
Final RAI - Braidwood, Units 1 and 2 - Amendment to Incorporate a Diurnal Curve (L-2024-LLA-0172)
Date:
Tuesday, March 17, 2026 8:22:54 AM
Dear Mr. Seawright,
By letter dated December 20, 2024 (Agencywide Documents Access and Management System (ADAMS) Accession No.ML24355A058), Constellation Energy Generation, LLC (the licensee) submitted a license amendment request (LAR) for Braidwood Station, Units 1 and 2 (Braidwood). The proposed LAR would modify the Braidwoods Technical Specifications (TSs) to change TS Surveillance Requirement (SR)3.7.9.2 to support an Ultimate Heat Sink (UHS) TS temperature limit that would reflect the diurnal effect that weather conditions have upon the UHS.
The U.S. Nuclear Regulatory Commission (NRC) staff has reviewed the submittal and determined that additional information is needed to complete its review. The specific question is found in the enclosed request for additional information (RAI). On March 13, 2026, the CEG staff indicated that a response to the RAIs would be provided by March 25, 2026.
If you have questions, please contact me at 301-415-2855 or via e mail at Scott.Wall@nrc.gov.
Scott P. Wall Senior Project Manager Plant Licensing Branch III Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation 301.415.2855 Scott.Wall@nrc.gov
Docket Nos.: STN 50-456, STN 50-457
Enclosure:
Request for Additional Information
cc: Listserv
REQUEST FOR ADDITIONAL INFORMATION
REGARDING LICENSE ADMENTMENT REQUEST
TO INCORPORATE A DIURNAL CURVE TO BRAIDWOOD STATION TECHNICAL
SPECIFICATIONS 3.7.9 FOR THE ULTIMATE HEAT SINK
CONSTELLATION ENERGY GENERATION, LLC
BRAIDWOOD STATION, UNITS 1 AND 2
DOCKETNOS.STN50456 AND STN50457
By letter dated December 20, 2024 (Agencywide Documents Access and Management System (ADAMS) Accession No.ML24355A058), Constellation Energy Generation, LLC (the licensee) submitted a license amendment request (LAR) for Braidwood Station, Units 1 and 2 (Braidwood). The proposed LAR would modify the Braidwoods Technical Specifications (TSs) to change TS Surveillance Requirement (SR)3.7.9.2 to support an Ultimate Heat Sink (UHS) TS temperature limit that would reflect the diurnal effect that weather conditions have upon the UHS.
The U.S. Nuclear Regulatory Commission (NRC) staff determined that the following information is needed to complete its review.
Instrumentation & Controls Branch (EICB) Questions
EICB-RAI-1 (Audit Item 1)
Regulatory Requirements
Braidwood is designed in accordance with the Appendix A to Title 10 of the Code of Federal Regulations (10CFR) Part 50, General Design Criteria for Nuclear Power Plants (GDC) as described in updated final safety analysis report (UFSAR), Revision 20, Chapter3 (ML24351A216). The following GDC is applicable:
Criterion 13 - Instrumentation and control. Instrumentation shall be provided to monitor variables and systems over their anticipated ranges for normal operation, for anticipated operational occurrences, and for accident conditions as appropriate to assure adequate safety, including those variables and systems that can affect the fission process, the integrity of the reactor core, the reactor coolant pressure boundary, and the containment and its associated systems. Appropriate controls shall be provided to maintain these variables and systems within prescribed operating ranges.
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Background===
The December 20, 2024, LAR references NRC letter dated July 26, 2016, BRAIDWOOD STATION, UNITS 1 AND 2 - ISSUANCE OF AMENDMENTS RE: ULTIMATE HEAT SINK TEMPERATURE INCREASE (CAC NOS. MF4671 AND MF4672) (ML16133A438), which approved the license amendment request in letter dated August 19, 2014 (ML14231A902).
As part of the staffs review of the August 19, 2014, LAR the NRC staff reviewed calculations and procedures during an audit (ML15232A589) to validate instrument uncertainty relationship to the UHS water temperature change.
Question
Please provide calculation for each value of the UHS diurnal curve temperature in LAR figure 3.7.9-1 which takes into account the precision instruments uncertainties.
In the summary of the calculation, please indicate how the as-left and as-found surveillance test acceptance criteria were determined.
Containment & Plant Systems Branch (SCPB) Questions
SCPB-RAI-1 (Audit Question 4)
Regulatory Requirements
The following GDCs are applicable:
Criterion 2 - Design bases for protection against natural phenomena.
Structures, systems, and components important to safety shall be designed to withstand the effects of natural phenomena such as earthquakes, tornadoes, hurricanes, floods, tsunami, and seiches without loss of capability to perform their safety functions. The design bases for these structures, systems, and components shall reflect: (1) Appropriate consideration of the most severe of the natural phenomena that have been historically reported for the site and surrounding area, with sufficient margin for the limited accuracy, quantity, and period of time in which the historical data have been accumulated, (2) appropriate combinations of the effects of normal and accident conditions with the effects of the natural phenomena and (3) the importance of the safety functions to be performed.
Criterion 44 - Cooling water. A system to transfer heat from structures, systems, and components important to safety, to an ultimate heat sink shall be provided. The system safety function shall be to transfer the combined heat load of these structures, systems, and components under normal operating and accident conditions.
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Background===
The NRC staff is requesting information that addresses the requirements of GDC 2 regarding the capability of structures housing the UHS and the UHS itself to withstand the effects of natural phenomena will be considered acceptable if the guidance of Regulatory Guide (RG)1.27, Ultimate Heat Sink for Nuclear Power Plants, Revision3 (ML14107A411) are appropriately addressed. In addition, the NRC staff requests information that addresses the requirements of GDC 44 regarding consideration of the cooling water system will be considered acceptable if the guidance of RG 1.27.
RG 1.27 states, in part:
Transient analyses used to predict the maximum intake water temperature to the plant and the maximum 30-day water usage should be based on regional climatological data, with substantiation of the conservatism of the data for
site use. The climatological measurements used for this analysis should be based on a recent period of record at least 30 years in length and should be demonstrated to be representative of conditions that may occur at the site.
Question
The LAR indicates that temperature used in analysis is from pre-2012. A severe weather-related event occurred at Braidwood in 2012 resulting in a Notice of Enforcement Discretion (NOED) (12-3-001) for Braidwood UHS elevated temperature (ML12194A681). The NRC staff is unclear whether current weather data (beyond 2012 to current) conditions were addressed in the analysis. Since the TS change is prompted by recent elevated atmospheric temperatures:
Provide a discussion of more recent elevated ambient temperature conditions and potential impact on bounding UHS analysis.
Confirm pre-2012 weather data used in Braidwood analysis remains representative and bounding of current climate conditions.
SCPB-RAI-2 (Audit Question 15)
Regulatory Requirements
The regulation in 0CFR50.36, Technical specifications, provides the regulatory requirements for the content of the TS. It requires, in part, that a summary statement of the bases for such specifications shall be included by applicants for a license authorizing operation of a production or utilization facility. Specifically, 10 CFR 50.36(c) requires that TS include items in five specific categories related to station operation. These categories are (1) safety limits, limiting safety system settings, and limiting control settings; (2) LCOs; (3) Surveillance requirements; (4)design features; and (5) administrative controls.
The regulation in 10 CFR 50.36(c)(2)(i), Limiting conditions for operation, states, in part, that TS will include LCOs, which are the lowest functional capability or performance levels of equipment required for safe operation of the facility. Section50.36(c)(2)(i) further states that [w]hen a limiting condition for operation of a nuclear reactor is not met, the licensee shall shut down the reactor or follow any remedial action permitted by the technical specifications until the condition can be met.
GDC Criterion44 is applicable.
Issue
Constellations LAR of December 20, 2024, Attachment 1 Section 3.1, UHS Structure and Evaluation, states, in part:
Equipment Heat Load
The heat load on the UHS is determined based on a unit undergoing a LOCA
[Loss-of-coolant accident] concurrent with a LOOP [loss-of-coolant accident]
and the other unit going through a normal shutdown from maximum power.
The proposed UHS temperature limit does not impact the UHS heat load as inputs to the limiting LOCA accident are not affected.
A separate project has the potential to impact the heat load on the UHS. Initial loading of Framatome fuel (GAIA) is scheduled for the fall 2025 refueling outage for Braidwood Unit 1 and spring 2026 refueling outage for Braidwood Unit 2 (Reference 2). Therefore, the new UHS temperature limit curve will be in effect at the time of the GAIA fuel transition. The potential change is due to the heat load to the residual heat removal (RHR) heat exchanger and the RCFCs following a Large Break LOCA (LBLOCA).
The GAIA fuel results in higher core stored energy. The impact of higher energy on the containment pressure, temperature, and recirculation sump temperature following a LBLOCA has been evaluated in support of the GAIA LAR. Additional heat removal from the RHR heat exchanger and RCFCs is not credited in the calculation of the higher containment temperature, pressure, and recirculation sump water temperature. Therefore, the design basis heat load to the CC heat exchanger and RCFCs is not affected, ensuring no impact to the supporting analyses or conclusions of this LAR.
Analysis No. ATD-0109, Revision 5 Thermal Performance of UHS During a Postulated Loss of Coolant Accident has been provided for the NRC staffs review on the Curtis Wright MetaStor e-portal as part of the ongoing staffs audit pertaining to Braidwoods LAR of December20,2024 (i.e., UHS Diurnal Curve review).
Section 4.6 Heat Load to the UHS of ATD-0109, Revision 5 indicates that the heat load rejected to the UHS is taken from ATD-0063, [Ref. 5.2]. Reference 5.2 indicates that ATD0063, Revisions 5 - 5A are dated 2-27-2022.
Constellations LAR of May 28, 2024 (ML24149A126), and the NRC staffs safety evaluation (SE) for the subsequently issued amendments of August 21, 2025 (ML25153A008), both pertain to the transitioning of the Braidwood Units to Framatome GAIA fuel. In neither of these two documents is there any concise discussion with respect to the impact of heat loads on the UHS and compliance with the requirements of Criterion 44.
From its read of Section 3.5, Containment Integrity, and Section 3.5.2, Peak Containment Temperature, of the staff's SE datedAugust 21, 2025, the NRC staff notes that, while the design basis heat load to the CC heat exchanger and RCFCs may not be affected (i.e.
changed) as stated by Constellation in the LAR of December 20, 2024, it appears that the actual heat load ultimately rejected to the UHS would be increased both during a LOCA and most likely during normal operation of the two Braidwood Units.
Question
Provide confirmation that the ATD-0063 revision used in the derivation of the Heat Load to the UHS, as invoked in Section 4.6 Heat Load to the UHS of ATD-0109, fully envelopes any increased UHS heat load values due to Constellations ongoing transition to Framatome GAIA fuel.