RS-21-077, License Amendment to Revise Technical Specification 3.7.9, Ultimate Heat Sink

License Amendment to Revise Technical Specification 3.7.9, Ultimate Heat Sink

ML21214A331
Person / Time
Site:	Braidwood
Issue date:	08/02/2021
From:	Gullott D Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RS-21-077
Download: ML21214A331 (38)

Text

4300 Winfield Road Warrenville , IL 60555 Exelon Generation 630 657 2000 Office RS-21-077 10 CFR 50.90 August2,2021 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Braidwood Station, Units 1 and 2 Renewed Facility Operating License Nos. NPF-72 and NPF-77 NRC Docket Nos. STN 50-456 and STN 50-457

Subject:

License Amendment to Revise Braidwood Station, Units 1 and 2, Technical Specification 3.7.9, "Ultimate Heat Sink" In accordance with 10 CFR 50.90, "Application for amendment of license, construction permit, or early site permit," Exelon Generation Company, LLC (EGC), is submitting a request for amendment to Renewed Facility Operating License Nos. NPF-72 and NPF-77 for Braidwood Station, Units 1 and 2 (Braidwood).

The proposed amendment adds two Required Actions and associated Completion Times to Technical Specification (TS) 3.7.9, "Ultimate Heat Sink," for an inoperable Ultimate Heat Sink (UHS) due to the average water temperature.

The proposed amendment also revises TS 3.7.9 Surveillance Requirement (SR) 3.7.9.2 to delete the temporary allowance for the UHS average water temperature of 102.8°F until September 30, 2021. This temporary change to the SR was implemented by Amendment No.

222 to Renewed Facility Operating License No. NPF-72 and Amendment No. 222 to Renewed Facility Operating License No. NPF-77 for the Braidwood Station , Units 1 and 2, respectively, as documented in NRC Safety Evaluation Report (SER) dated July 13, 2021 . (ADAMS Access No.

ML21154A046). This is an administrative change.

Past meteorological and atmospheric conditions have resulted in the TS UHS temperature being challenged . These conditions include elevated air temperatures, high humidity, and low wind speed. These conditions are not predictable and future occurrence may challenge plant operation.

As discussed in Regulatory Guide (RG) 1.27, Revision 2, "Ultimate Heat Sink for Nuclear Power Plants," the predicted response of the UHS temperature to the design basis event is a function of the historical weather including the diurnal variations. This proposed amendment is consistent with Braidwood Station's licensing basis (i.e., RG 1.27 Revision 2). The purpose of the UHS TS temperature limit is to limit the initial UHS temperature such that the maximum UHS temperature (i.e., the temperature of the cooling water supplied to the plant safety systems from the UHS) experienced during the UHS design basis event would not exceed the design limit of the plant equipment cooled by the UHS.

August2,2021 U.S. Nuclear Regulatory Commission Page 2 The attached amendment request is subdivided as follows :

• Attachment 1 provides an evaluation of the proposed changes.

• Attachment 2 provides the current TS pages with the proposed changes indicated with markups.

• Attachment 3 provides the current TS Bases pages with the proposed changes indicated with markups. The TS Bases pages are provided for information only and do not require NRC approval.

• Attachment 4 provides the revised clean TS pages.

In accordance with 10 CFR 50.91 , "Notice for public comment; State consultation ,"

paragraph (b), EGC is notifying the State of Illinois of this application for license amendment by transmitting a copy of this letter and its attachments to the designated State Official.

EGC requests approval of the proposed license amendment by August 2, 2022 to support plant operation in the Summer 2022 with the potential of hot weather and drought conditions resulting in sustained elevated UHS temperatures. Once approved, the amendment will be implemented within 30 days.

The proposed amendment has been reviewed and approved by the Braidwood Station Plant Operations Review Committee in accordance with the requirements of the EGC Quality Assurance Program.

There are no regulatory commitments contained in this letter. Should you have any questions concerning this letter, please contact Mr. Phillip A. Henderson at (630) 657-4727.

I declare under penalty of perjury that the foregoing is true and correct. Executed on the 2nd day of August 2021.

Respectfully, Gui Iott, Digitally signed by Gullett, David M.

David M.

Date: 2021.08.02 13:26:13 -05'00' David M. Gullatt Director Licensing Exelon Generation Company, LLC Attachments :

1. Evaluation of Proposed Changes

2. Mark-up of Proposed Technical Specification Page Change

3. Mark-up of Proposed Technical Specification Bases Pages Changes - For Information Only

4. Revised Clean Technical Specifications Bases Pages

August2,2021 U.S. Nuclear Regulatory Commission Page 3 cc: Illinois Emergency Management Agency - Division of Nuclear Safety NRC Regional Administrator- Region Ill NRC Senior Resident Inspector - Braidwood Station

Attachment 1 Evaluation of Proposed Changes

Subject:

License Amendment to Revise Braidwood Station, Units 1 and 2, Technical Specification 3.7.9, "Ultimate Heat Sink" 1.0

SUMMARY

DESCRIPTION 2.0 DETAILED DESCRIPTION

4.0 REGULATORY EVALUATION

4.1 Applicable Regulatory Requirements/Criteria 4.2 No Significant Hazards Consideration Determination 4.3 Conclusions

6.0 REFERENCES

Page 1 of 24

Attachment 1 Evaluation of Proposed Changes 1.0

SUMMARY

DESCRIPTION In accordance with 10 CFR 50.90, "Application for amendment of license, construction permit, or early site permit," Exelon Generation Company, LLC (EGC), is submitting a request for amendment to Renewed Facility Operating License Nos. NPF-72 and NPF-77 for Braidwood Station, Units 1 and 2 (Braidwood).

Braidwood has little margin between the ultimate heat sink (UHS) temperature limit, which is the limit in the Technical Specification (TS) Surveillance Requirement (SR), and the peak UHS temperatures that can occur during the summer months. Various design and licensing bases must be evaluated to address UHS temperatures which are higher than the 102°F TS SR limit.

The purpose of this LAR describes a process which will support the implementation of a new TS Required Action that would allow the UHS TS SR to be exceeded for a limited period of time, which is 7 days. The process credits engineering evaluations that demonstrate compliance with the safety analyses.

This proposed amendment utilizes existing margin in Design Analysis to offset the increase in the TS SR UHS temperature based on actual or projected plant conditions at the time of entry into the new TS Required Actions A.1.1 and A.1.2.

Past summer meteorological and atmospheric conditions have resulted in the TS UHS temperature limit being challenged . These conditions include elevated air temperatures, high humidity, and low wind speed. The UHS design analysis methodology is based on Regulatory Guide (RG) 1.27, Revision 2, "Ultimate Heat Sink for Nuclear Power Plants," and NUREG-0693, "Analysis of Ultimate Heat Sink Cooling Ponds," dated November 1980.

The proposed amendment would add a new Required Action A.1 .1, "Verify UHS temperature at or below the maximum analyzed temperature limit," with a Completion Time of "Immediately" and "Once every 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> thereafter" to the current Condition A, which states: "UHS inoperable due to average water temperature." This new Required Action provides additional monitoring during which Operations would monitor and trend diurnal cooling effects of the lake until SR 3.7.9.2 is met.

The proposed amendment would also add a new Required Action A.1.2, "Verify UHS average water temperature within SR 3.7.9.2 ," with a Completion Time of 7 days to the current Condition A. This approach is similar to the Pressurized Water Reactor Owners Group (PWROG) conceptual program for temporary relaxation of UHS peak temperature SR (ADAMS Accession No. ML20223A015).

Additionally, the proposed amendment would revise TS Surveillance Requirement (SR) 3.7.9.2 to delete the following text:

" .. _s; 102.8°F until September 30, 2021. After September 30, 2021, verify average water temperature of UHS is ..."

This license amendment is being requested to allow the TS temperature limit of the cooling water supplied to the plant from the UHS to be >102°F for 7 days. During the 7 days period, the maximum UHS temperature will be limited to the value that has been evaluated to ensure the results of the Braidwood Station current licensing basis analyses and evaluations are not exceeded with UHS temperature greater than 102°F. The proposed amendment allows Page 2 of 24

Attachment 1 Evaluation of Proposed Changes sufficient time for the UHS temperature to return below the 102°F TS limit prior to having to perform an evolution to shutdown both Braidwood units and place each unit through an unnecessary transient and thermal cycle.

The current maximum analyzed average UHS water temperature limit is 102.8°F as documented in NRC SER dated July 13, 2021 (ADAMS Access No. ML21154A046).

The average UHS water temperature limit will be documented in controlled station procedures.

2.0 DETAILED DESCRIPTION 2.1 Proposed Changes The proposed changes to TS 3.7.9 are shown in Attachment 2 and are as follows:

The current TS 3.7.9 Actions for Condition A states:

CONDITION REQUIRED ACTION COMPLETION TIME A. UHS inoperable due to A.1 Be in MODE 3. 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> average water temperature. AND A.2 Be in MODE 5. 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> Page 3 of 24

Attachment 1 Evaluation of Proposed Changes The proposed TS 3.7.9 Actions for Condition A would state:

CONDITION REQUIRED ACTION COMPLETION TIME A. UHS inoperable due to A.1.1 Verify UHS average Immediately average water water temperature at temperature. or below the maximum analyzed temperature limit.

AND Once per 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> thereafter AND A.1.2 Verify UHS average 7 days water temperature within SR 3.7.9.2.

OR A. 2.1 Be in MODE 3. 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> AND A. 2.2 Be in MODE 5. 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> The current TS SR 3.7.9.2 states:

Verify average water temperature of UHS is ~ 102.8°F until September 30, 2021. After September 30, 2021, verify average water temperature of UHS is ~ 102°F.

The proposed TS SR 3.7.9.2 would state:

Verify average water temperature of UHS is~ 102°F.

2.2 Background

The UHS consists of an excavated essential cooling pond integral with the main cooling pond.

The excavation is made such that the essential pond remains intact in the event of failure of the Category II retaining dikes impounding the main cooling pond. Under normal circumstances, the essential cooling pond is indistinguishable from the remainder of the Braidwood cooling pond . The essential cooling water intakes and discharges are arranged, however, to extract water from and return water to the cooling pond in that portion which would become the Page 4 of 24

Attachment 1 Evaluation of Proposed Changes essential cooling pond, should failure of the Category II cooling pond retaining dikes occur. The maximum operating level of the essential cooling pond is assumed to be 590 feet above mean sea level.

The main cooling pond has a storage volume of 22,300 acre-feet at the normal water elevation (approximately 596 ft). The essential cooling pond has an analyzed gross volume of 555.8 acre-feet at the 590 ft elevation. The Design Basis of the UHS assumes the dikes around the main cooling pond fail at the start of the event and none of the water volume above the 590 feet elevation is credited as a heat sink.

The volume of the UHS is sized to permit the safe shutdown and cooldown of both Braidwood Station units for a minimum 30-day period during a OBA with no additional makeup water source. The UHS is designed to withstand the separate occurrence of either the safe shutdown earthquake or the probable maximum flood on the cooling pond . The UHS provides a heat sink for process and operating heat from safety related components during a transient or accident, as well as during normal operation. The UHS dissipates residual heat after reactor shutdown and after an accident through the cooling components of the Essential Service Water (SX)

System and the Component Cooling Water (CC) system, which are the principal systems at Braidwood Station that utilize the UHS to dissipate residual heat. The UHS also provides a source of emergency makeup water for the spent fuel pool and can provide water for fire protection equipment. Non-Essential Service Water (WS) pumps and Circulating Water (CW) pumps also take suction from the UHS during normal operation, however, operation for post-accident conditions is not considered since the WS and CW pumps are shut down before the UHS level reaches the minimum required water level for plant operation at 590 feet.

The SX system takes suction from intake lines running from Safety Category I essential cooling pond to the auxiliary building where four SX pumps (two per unit) supply safety-related loads and components essential to safe shutdown. These include cubicle coolers, pump coolers, diesel engine coolers, CC heat exchangers, Reactor Containment Fan Coolers (RCFC) and chiller condensers. The CC system provides cooling water to the residual heat removal system, chemical and volume control system, reactor coolant system and process sampling system.

Updated Final Safety Analysis Report (UFSAR) Figure 2.4-47, "Essential Cooling Pond," shows the layout of the SX supply and discharge piping along with the Circulating Water supply and discharge piping. Relevant elevations for the cooling pond are also included in this figure.

The Braidwood limiting UHS OBA (i.e., that event that results in the maximum heat load on the UHS) is one unit undergoing post-Loss of Coolant Accident (LOCA) cooldown concurrent with a Loss of Offsite Power (LOOP), in conjunction with the other unaffected unit undergoing a safe non-accident shutdown. This scenario assumes the worst case single failure of the manmade structure (i.e., the Category II retaining dikes) that encloses the main cooling pond.

The limit on the UHS temperature is meant to restrict the initial UHS temperature such that the maximum temperature of the SX system supplied to the plant safety systems from the UHS experienced during the UHS design basis event would not result in plant equipment cooled by the UHS to operate outside design limits.

This limiting OBA includes three sources of heat energy to be transferred by the SX system after a LOCA:

• Containment heat removal via the RCFCs, Page 5 of 24

Attachment 1 Evaluation of Proposed Changes

• Containment heat and reactor residual heat removal via the containment sumps, and

• Engineered Safety Features (ESF) equipment heat loads (e.g., ESF equipment coolers and room coolers) and the Main Control Room chiller.

The impact of the higher UHS temperature and the method of evaluation for each source of heat energy will be discussed further in Section 3.0 , Technical Evaluation.

Historical information related to the Braidwood UHS temperature limit indicates an increasing trend for the UHS temperature . The conditions that challenge the UHS water temperature limit are not predictable, but future occurrence will challenge plant operation. The allowance to exceed the 102°F limit is permitted as long as the UHS temperature remains below analyzed values. This change allows EGC to control UHS temperature excursions above 102 °F. This request does not have negative consequences as the maximum UHS temperature will be maintained below the analyzed limit.

The Braidwood Station Safety Evaluation Report (NUREG-1002, 1983, Section 2.4) documents the original calculated maximum UHS temperature as 94°F. The NRC found it acceptable considering the design limit temperature was 100°F. The thermal performance of the Braidwood Station UHS was originally developed based on the initial maximum UHS temperature of 98°F. On June 13, 2000 , the U.S . NRC issued an amendment to increase the allowable UHS temperature from 98°F to 100°F. Due to changes in meteorological conditions that resulted in the TS UHS temperature limit being challenged , in 2001 and 2012 EGC submitted and obtained NRC approval for a temporary increase in the temperature limit to 102°F. A license amendment request was submitted in 2014 to permanently increase the UHS allowable temperature to 102°F.

3.0 TECHNICAL EVALUATION

This section discusses the current margins in Braidwood engineering analyses that support a UHS limit higher than 102°F.

The UHS is the heat sink for heat removed from the reactor core following all accidents and anticipated operational occurrences in which the unit is cooled down and placed on Residual Heat Removal (RHR) operation. The operating limits are based on conservative heat transfer analyses for the worst case loss of coolant accident (LOCA). The UHS is designed in accordance with Regulatory Guide (RG) 1.27, "Ultimate Heat Sink for Nuclear Power Plants, "

Revision 2.

The current design basis analyses use an initial SX temperature of 102°F. This basis is documented and approved as part of the NRC's approval of TS amendments 189 and 189 (ADAMS Accession No. ML16209A218). On July 26, 2016, the U.S . NRC approved the increase of allowable TS UHS temperature from 100°F to 102°F. An additional evaluation was completed in 2020 to support a temporary increase to 102.8°F as documented in NRC SER dated September 24 , 2020 (ADAMS Access ML20245E419). The average UHS water temperature limit was temporarily increased to 102.8°F until September 30, 2021 as documented in NRC SER dated July 13, 2021 (ADAMS Access ML21154A046). The value of 102.8°F is the current maximum average UHS temperature that has been evaluated.

Page 6 of 24

Attachment 1 Evaluation of Proposed Changes The technical discussion that follows outlines the scope of formal evaluations that will be performed to support a higher analyzed UHS temperature limit under proposed TS Required Action A.1 .1.

The conditions that challenge the UHS water temperature limit are not predictable, but future meteorological conditions may challenge plant operation. The allowance to exceed the current TS SR 102°F limit is permitted as long as the UHS temperature remains below the Required Action A.1 .1 value as determined by Engineering. This value will be documented in an engineering evaluation prior to summer periods where extreme temperatures are expected to persist for several days. This change allows EGC to control UHS temperature excursions above 102°F based on current plant conditions and external weather events. This request does not have negative consequences as the maximum UHS temperature will be maintained below the value determined by the conservative engineering evaluations to ensure SSCs can perform their design basis functions and analyses continue to meet current acceptance criteria. The current design analyses discussed in this LAR have considerable margins in several areas. The new TS Required Action A.1.1 engineering analysis will demonstrate that the design basis and equipment operations will be ensured .

This proposed change would allow the natural diurnal cooling behavior of the lake to occur in restoring the UHS temperature below the TS SR limit without having to shutdown both Braidwood units and place each unit through an unnecessary thermal cycle evolution.

The UHS supplies water to the SX system, therefore, the UHS and SX for certain circumstances, can be used interchangeably in this LAR.

3.1 UHS Temperature Profile As discussed in the basis for TS amendments 189, EGC determined that with UHS starting at a temperature of 102°F, the highest UHS temperature during a worst case LOCA would be 105.2°F. Figure 1 below shows the temperature response for this worst case LOCA at a start time of 0300. In support of TS amendment 189, EGC used 106°F to analyze the post-accident performance of the equipment served by SX except for the Reactor Containment Fan Coolers (RCFC) which used 104°F. For higher initial temperatures, the profile is expected to be typical with higher peaks. The UHS temperature remains below the initial temperature for over 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> from the start of the event, except for a short and small (< 0.5 °F) excursion at about 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.

Page 7 of 24

Attachment 1 Evaluation of Proposed Changes Figure 1 UHS Te mperature Profile - Limiting Case 3 SX Pumps - Event Start 3 AM 106

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0.0 0 .5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Days Following Accident 3.2 Equipment Supported by SX The Essential Service Water System (SX) takes suction from the UHS to the Auxiliary Building where the SX pumps supply the safety related loads and components required for safe shutdown. These include cubicle coolers, pump coolers , diesel engine coolers, containment coolers, Component Cooling (CC) water heat exchangers and chillers' condensers. The SX system is divided into two redundant trains per unit. SX is required for normal operation, Loss of Coolant Accident (LOCA), Loss of Off-site Power (LOOP) and shutdown modes of operation.

The current post-accident performance of the equipment served by SX has been analyzed for an SX temperature of up to 106°F. These analyses use design fouling values and tube plugging limiting criteria. The actual tube plugging is lower than analyzed and the fouling values are lower in Summer months due to higher SX flows through the cooling equipment. Therefore, the current design analyses that have been completed for the 106°F UHS temperature are conservative. Additional discussion was provided in Reference 4.

The component cooling heat exchanger tube plugging analysis also uses a supply SX temperature of 106°F. This is conservative because the timing of the limiting heat load is within 30 minutes from accident initiation, when the component cooling system is configured to supply the Residual Heat Removal heat exchanger, thus cooling the water from the Containment Recirculation sumps. The containment sump water temperature is over 120°F lower (-131 °F vs

-258°F, Unit 1 is limiting) when the UHS reaches its peak temperature at over 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> from the start of the event.

Page 8 of 24

Attachment 1 Evaluation of Proposed Changes In the event the UHS Temperature exceeds the 102°F SR limit during operation, the Required Action A.1 .1 will be performed for the applicable components serviced by the SX system. The temporary increase in the UHS temperature for a duration of 7 days will be justified by pre-existing engineering evaluations. The evaluation will ensure that all components cooled by the UHS continue to operate within their design limits. The temporary increase will be controlled through Braidwood's administrative procedures.

The average TS UHS water temperature limit was temporarily increased to 102.8°F until September 30 , 2021 as documented in NRC SER dated July 13, 2021 (ADAMS Access No.

ML21154A046). The value of 102.8°F is the current maximum average UHS temperature that has been evaluated .

Discussion of the potential effect of possible fish scales, occasional precipitation of solids in the cooling lake, other known conditions on design fouling values, and subsequent impact on margin were provided in References 4 and 6.

The fish scale event wh ich occurred in July 2020 did not result in adverse consequences on the SX system and did not result in adverse effects for the equipment that is cooled by the SX system. Since then , no additional fish scale event has been identified at Braidwood.

Braidwood's Lake Management strategy to prevent solids precipitation events is that of Managed Self Softening. This strategy utilizes chemical treatment together with the saturation characteristics of calcium carbonate to adjust the timing and the rate of the natural softening of the lake. Natural softening , or slow precipitation, is related to the saturation characteristics of calcium carbonate. Historical data shows that managed natural softening does not cause fouling of plant equipment. Therefore, fish scales and the natural softening of the cooling lake will not affect the fouling values used in the analyses and do not impact the margin for higher SX temperatures.

Based on the above, all equipment served by SX remains operable with elevated SX temperature.

The Reactor Containment Fan Coolers are addressed in the Accident Analyses section .

3.3 Impact on the Safety Analyses 3.3.1 Containment Integrity {UFSAR Chapter 6)

The SX system supplies the Reactor Containment Fan Coolers (RCFCs) post-accident. Two trains of containment cooling, each of sufficient capacity to supply 100% of the design cooling requirement, are provided. Each train consisting of two RCFCs is supplied with cooling water from a separate train of SX and is powered from a separate ESF bus. During all operating conditions , air is drawn from the upper volume of the containment approximately 50 feet above the operating floor by a return air riser (one riser for each RCFC unit). The return air is then routed through the SX cooling coils, the Chilled Water (WO) cooling coils , and the fan and discharge duct (one for each RCFC unit). The RCFC discharges directly into the lower containment volume. The WO chiller unit condensers are served by the SX return from the RCFC SX cooling coils. Upon receipt of an ESF signal, the WO condensers are automatically isolated from SX. In post-accident operation following an actuation signal, the RCFC fans are designed to start automatically in slow speed if not already running. If running in high (normal) speed, the fans automatically shift to slow speed . The fans are operated at the lower speed Page 9 of 24

Attachment 1 Evaluation of Proposed Changes during accident conditions to prevent adverse fan conditions from the higher mass atmosphere.

The temperature of the SX is an important factor in the heat removal capability of the fan units .

The heat removal for the RCFCs is an input to the Accident Analyses.

The Design Basis Safety Analyses use RCFC heat removal performance for an SX temperature of 104°F. This is acceptable because, except for a small excursion, the SX temperature remains below 104 °F for a period longer than the time of the calculated peak Containment pressure and temperature. This analysis and conclusion do not change with a higher initial UHS temperature because the peak Containment temperature and pressure occur early in the accident well before the UHS post-accident temperature increases above the RCFC analyzed temperature of 104 °F. This justification was approved by the NRG in TS amendment 189 (ADAMS Accession No. ML16209A218) and is described in more detail below.

The calculated UHS temperature profile shows the temperature initially decreases and remains below the starting temperature until about 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> after the event. A small excursion (< 0.5°F) above the initial temperature occurs at about 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. This small excursion is for a limited period (< 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />) and it is insignificant. By Engineering Judgment, higher initial UHS temperatures (up to 104 °F) support the RCFC heat removal performance used in the Design Basis Safety Analyses for at least 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

The containment pressures and temperatures have been significantly reduced from the calculated peak value at 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after the event. At 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, the containment pressure is approximately 30 psi lower than the calculated peak (about 10 psig vs Limiting Pressure U-1 42 .1 psig) and the containment temperature is approximately 80°F lower than the calculated peak (180°F vs 260°F). Similar margins are available for the Containment Sump water temperature . Therefore, the increase in the UHS temperature above 104°F after 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> will not result in exceeding any design criteria related to post-LOCA containment requirements. In addition, the heat removal curve used for the RCFCs is conservative because it is based on a tube plugging level of 10% while the actual tube plugging is < 2%.

For the Main Steamline Break accidents inside Containment, the calculated temperature is approximately 100°F lower at 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after the event. The LOCA event is bounding for peak calculated pressure. For this event the transient is terminated well before the RWST is drained down since only the charging and the safety injection pumps actuate during these events.

3.3.2 UFSAR Chapter 15 Safety Analyses The analysis of record for Braidwood Units 1 and 2 will be evaluated to confirm that the increased UHS water temperature will have no or a negligible impact on Full Spectrum loss of coolant accident (FSLOCA)), long term core cooling (LTC) and non-LOCA analyses.

The LOCA analyses (and some non-LOCA transients) assume the minimum and/or the maximum water temperature of the Emergency Core Cooling System (ECCS) and the maximum cooling capacity of the reactor containment fan coolers (RCFC). Both of these assumptions can be potentially impacted by the assumption of the SX temperature . These impacts are addressed below.

Page 10 of 24

Attachment 1 Evaluation of Proposed Changes 3.3.3 Peak Clad Temperature Analyses On December 28, 2020 , the U.S . NRG approved license amendment 219 for Braidwood to replace current approved loss-of-coolant accident (LOCA) methodologies with a single newer approved LOCA methodology, "the FULL SPECTRUM' 1 LOCA Evaluation Model (FSLOCA' EM)," (ADAMS Accession No. ML20315A516). The amendment has been implemented for Braidwood Unit 1 and will be implemented for Braidwood Unit 2 in Fall 2021.

Therefore , the following discussion for Full Spectrum LOCA (FSLOCA) is applicable to both Braidwood Unit 1 and Unit 2.

Full Spectrum LOCA (FSLOCA)

The Full Spectrum LOCA (FSLOCA) analyses cover the full spectrum of break sizes. The break sizes considered in the Westinghouse FSLOCA EM include any break size in which break flow is beyond the capacity of the normal charging pumps, up to and including a double-ended guillotine (DEG) rupture of an RCS cold leg with a break flow area equal to two times the pipe area, including what traditionally are defined as Small and Large Break LOCAs.

The break size spectrum is divided into two regions. Region I includes breaks that are typically defined as Small Break LOCAs (SBLOCAs). Region II includes break sizes that are typically defined as Large Break LOCAs (LBLOCAs). The Region II analysis simulations include breaks above 1.0 ft2 break area, up to a maximum size of a double ended guillotine break.

The calculated peak clad temperatures (PCT) are provided below:

Region I Time of PCT Region II Time of PCT 10 CFR 50.46 Criterion Braidwood 1,181 °F 1,205 sec 1,641 °F 4.1 sec 2,200°F Unit 1 (Offsite power Available )

1,643°F 9.1 Sec (Loss of Offsite Power)

Braidwood 1,169°F 974 sec 1,752 °F 107 sec 2,200°F Unit 2 (Offsite power Available )

1,711 Of 35 Sec (Loss of Offsite Power)

In the event of a large break LOCA (LBLOCA), the ECCS water is initially drawn from the refueling water storage tank (RWST). When the RWST level decreases to the L0-2 setpoint (46.7% level), the ECCS pumps are realigned to take suction from the Containment Recirculation sump. For the FSLOCA analyses, a conservative minimum switchover time of 1,038 seconds was calculated using the minimum usable refueling water storage tank (RWST) volume , maximum containment spray flow, and a conservative total SI flow rate (injected +

spilled). For this initial calculation, it was conservatively assumed that the containment spray flow and safety injection (SI) flow begin at the start of the transient.

1 FULL SPECTRUM and FSLOCA are trademarks or registered trademarks of Westinghouse Electric Company LLC, its subsidiaries, and/or affiliates in the United States of America and may be registered in other countries through the world . All rights reserved . Unauthorized use is strictly prohibited. Other names may be trademarks of their respective owners.

Page 11 of 24

Attachment 1 Evaluation of Proposed Changes For the Region 11 analyses, the time of the PCT is well within the time of the ECCS switchover.

The Region II analyses transients are terminated at 300 seconds.

The transient termination time was determined for each break size in the Region I break spectrum studies based on the criteria defined in Section 31.2.1 of WCAP-16996-P-A, Revision

1. For breaks larger than approximately 4 inches in diameter, transient termination occurred before the initial conservative minimum switchover time . For smaller breaks, transient termination occurred after the initial conservative minimum switchover time.

For the smaller breaks, containment pressure calculations were performed for select cases to determine a more realistic spray actuation time based on the spray actuation setpoint. These calculations showed that containment spray actuation would not occur until at least several hundred seconds after the break initiation and would not occur at all for the smallest breaks.

The switchover time for each of the smaller breaks was then recalculated using the more realistic spray actuation time. The switchover time for a 3. 7 inch break was determined to be 1, 778 seconds. For all of the smaller breaks, transient termination occurred before the refined minimum switchover time.

Containment Model For the Region II analysis, the containment pressure is calculated for each LOCA transient in the analysis using the COCO code . The COCO containment code is integrated into the WCOBRA/TRAC-TF2 thermal-hydraulic code. The transient-specific mass and energy releases calculated by the thermal-hydraulic code at the end of each timestep are transferred to COCO.

COCO then calculates the containment pressure based on the containment model and the mass and energy releases, and transfers the pressure back to the thermal-hydraulic code as a boundary condition at the break, consistent with the methodology in Section 25.6 of WCAP-16996-P-A. The containment model for COCO calculates a conservatively low containment pressure. The heat removal curve used for the RCFCs is based on a minimum SX temperature of 32°F.

For the Region I analysis, the containment pressure is not calculated; a constant pressure equal to the initial containment pressure is modeled at the break.

Summarv For the Region I analysis, a refined minimum switchover time was calculated based on more realistic Containment Spray actuation time. The results demonstrated that transient termination, and thus PCT occurred before the refined minimum switchover time for all break sizes in the Region I break spectrum Studies. Therefore, changes in SX temperature does not impact the results of the FSLOCA Analyses.

For the Region II analysis, the PCT related transient is over while the ECCS is drawing suction from the RWST. Since SX temperature has no effect on the RWST water temperature, an increase in SX temperature will not impact the calculated PCT.

The Essential Service Water (SX) system, and thus the UHS, is the safety related water source for the Auxiliary Feedwater (AF) system. For the Region I analysis, the FSLOCA analysis uses 113.5°F for the temperature of the Auxiliary Feedwater make-up to the secondary side of the Page 12 of 24

Attachment 1 Evaluation of Proposed Changes steam generators. The 113.5°F temperature is bounding with respect to any credible UHS temperature increase above 102 °F.

During the long term, when the ECCS water is drawing suction from the sump, the SX temperature can have an effect on the peak clad temperatures. However, at this point in the transient, the peak clad temperatures are significantly lower, and an increase in SX temperature will not result in the clad temperatures greater than the calculated peak clad temperatures.

Non-LOCA Analyses For three non-LOCA events, main steam line break (MSLB), feed line break (FLB) and steam generator tube rupture (SGTR) , the ECCS is modeled and assumed to operate. For these events the transient is terminated well before the RWST level lowers to the switchover setpoint since only the charging and the safety injection pumps actuate and inject during these events.

The increase in SX temperature does not have a detrimental impact on the MSLB, FLB and the SGTR results; therefore the engineering evaluation will not consider these events when determining a temporary UHS temperature.

3.3.4 Long Term Core Cooling and Hot Leg Switchover Analysis The Component Cooling Heat Exchangers have been evaluated and have been found to be capable of removing the required heat load associated with the assumptions in the Containment Integrity Analysis with an SX supply temperature of 106 °F. The peak value for required heat removal is at about 30 minutes into the event. The UHS temperature profile shows the UHS temperature at this time is below the initial temperature and decreasing.

The Hot Leg Switchover analysis for Braidwood Station determined that switchover must occur at 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> after the event. Based on the UHS temperature profile, the SX temperature at 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> is below the temperature at the start of the event. The component cooling heat exchanger tube plugging analysis uses a supply SX temperature of 106°F. This is conservative because the timing of the limiting heat load is within 30 minutes from accident initiation, when the component cooling system is configured to supply the Residual Heat Removal heat exchanger, thus cooling the water from the Containment Recirculation sumps. The containment sump water temperature is over 120°F lower (-131 °F vs -258°F, Unit 1 is limiting) when the UHS reaches its peak temperature at over 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> from the start of the event.

3.3.5 CC System to RCPs The maximum CC temperature to the Reactor Coolant Pumps (RCP) is 105°F during normal plant operation. This temperature limit is raised to 120°F for a short period (3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />) when the Residual Heat Removal system is first used during RCS cooldown. The increase in CC temperature will be evaluated and determined to be acceptable.

Operating experience at Braidwood, with the cooling lake temperature approaching 100°F, indicates that exceeding the operating limit of 105°F can be limited by adjusting SX flow rates.

Shutdown criteria for the RCPs bearing temperatures will remain in effect so that the higher SX temperature will not have any adverse effects on the RCPs and their operation .

Page 13 of 24

Attachment 1 Evaluation of Proposed Changes 3.3.6 Other Analyses Other considerations, such as the impact to the UHS temperature on Generic Letter (GL) 96-06, "Assurance of Equipment Operability and Containment Integrity During Design-Basis Accident Conditions," and Station Blackout (SBO), will also be evaluated, as discussed below.

GL 96-06 U.S. Nuclear Regulatory Commission Generic Letter 96-06 indicated concerns for possible water hammer events following either a Loss of Coolant Accident (LOCA) or a Main Steam Line Break (MSLB) concurrent with a Loss of Offsite Power (LOOP). Under this scenario, the pumps that supply cooling water to the reactor containment fan coolers (RCFCs) and fans that supply air to RCFCs will temporarily lose power. Cooling water flow will stop due to the loss of pump head. Boiling may occur in RCFC tubes, causing steam bubbles to form in the RCFCs and pass into the attached Essential Service Water (SX) piping, creating steam voids. As service water pumps restart and the water column accelerates, accumulated steam in the fan coolers tubes and piping will condense which could result in a water hammer when the void closes.

Hydrodynamic loads introduced by such a water hammer event could potentially challenge the integrity and function of RCFC and associated cooling water system components, as well as pose a potential challenge to containment integrity.

The period of interest for the GL 96-06 concern of water hammer is the first few minutes post-accident, while the pumps and fans are restarting following load shed. The temperature used in this analysis is therefore the initial UHS temperature. The analysis of record reviewed the impact with an increase in SX temperature from 100°F to 102°F and determined that a slight increase in fluid temperature will not result in significant changes to the amount of voiding and thus negligible impacts to void collapse and the existing results of this analysis. A slight increase in the fluid temperature entering the coil will not result in significant changes to the amount of voiding in the coils. It is the pump restart that results in the void collapse which forces the water columns in the RCFCs to re-join. Small variations in fluid temperature will have negligible impact on fluid velocities at the void collapse and will not significantly impact the results of the analysis.

This qualitative assessment is supported by the results of the evaluation that was completed for a fluid temperature of 105°F (Reference 9).

Diesel Driven AF Pump Operation during Loss of All AC Power In the event of a loss of all AC power (i.e., Station Blackout or SBO), a diesel driven SX booster pump operates to provide cooling water to the diesel driven AF pump and engine cooler. Due to the configuration of the discharge piping to the lake, there is insufficient booster pump head to maintain once-through flow to the lake during this event. Thus, flow recirculates through various components back to the diesel driven SX booster pump suction. This results in isolation of the cooling water heat sinks and heat-up of the isolated SX loop during the SBO coping period.

Design analysis evaluates this transient and concludes that AF diesel engine jacket water temperature will not exceed the engine trip setpoint in 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />. The calculation evaluates a maximum UHS temperature of 102°F. The analysis used a plugging level of 5 tubes for the 102°F case. The analysis also determined that the allowed tube plugging decreases by two (2) tubes for each °F increase in the SX temperature.

Page 14 of 24

Attachment 1 Evaluation of Proposed Changes The actual numbers of tubes that are plugged for the heat exchangers (1/2SX01 K) is zero (0) for Unit 1 and one (1) for Unit 2. The actual plugging level supports a maximum SX temperature of 104°F.

3.4 Completion Time of 7 days The new Required Action A.1.1 will allow for Engineering to perform evaluations and analyses to demonstrate that the plant's safety related equipment will maintain its design function at the higher UHS temperature . The evaluations and analyses will be performed prior to forecasted conditions in which the UHS could exceed the surveillance requirement for average temperature to ensure present plant conditions support the increased temperature . Additionally, a Completion Time of "Once per 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> thereafter" will ensure that local precision monitoring of the UHS temperature occurs so that Operations can trend the diurnal cooling effects on the lake until SR 3.7.9.2 is met. Applicable Shiftly And Daily Operating Surveillances and administrative procedures will be revised to include this action. Additionally, the maximum analyzed UHS temperature limit will be documented in these procedures for reference by Operations.

Operations currently monitors the Ultimate Heat Sink (UHS) temperature by averaging the running Essential Service Water (SX) pump discharge temperatures. This temperature is recorded twice per day in the Shiftly And Daily Operating Surveillance when in Modes 1-4 (1/2BwOSR 0.1-1,2,3 and 1/2BwOSR 0.1-4 for Mode 4). When UHS temperature is >99.0F operations measures the UHS temperature locally at a spare thermowell using precision instrumentation. In addition, LCO 3.7.9 Tech Spec conditions and actions are controlled in administrative procedure 1/2BwOL 3.7.9, "LCOAR Ultimate Heat Sink (UHS) Tech Spec LCO 3.7.9."

If UHS temperature trends towards the maximum analyzed temperature limit, then Required Actions A.3 and A.4 will be performed to place the unit in Mode 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> AND Mode 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. The 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> monitoring periodicity is adequate to identify trends and reductions in margin to the maximum analyzed temperature limit within the safety analyses.

Based on historical data, the Completion Time of 7 days for Required Action A.1 .2 will allow for the UHS average water temperature to be returned within the Technical Specifications limit of 102°F, if the UHS is inoperable due to average UHS water temperature. This proposed change would allow the natural diurnal cooling behavior of the lake to occur in restoring the UHS temperature below the TS limit without having to shutdown both Braidwood units and place each unit through an unnecessary transient and thermal cycle evolution. A review of UHS temperatures from 2010 to 2021 show that peak temperatures on average occur during a 2-3 day period before changing atmospheric and weather conditions result in greater UHS cooling and temperature margins. The review identified three previous summer periods of peak temperatures that required at least 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> for natural cooling to increase UHS temperature margins as defined below:

Page 15 of 24

Attachment 1 Evaluation of Proposed Changes Peak UHS temperatures from July 20, 2011 to July 23, 2011 existed for a period of -72 hours before lowering due to natural cooling (Figure 2). This period of temperature excursion did not require a licensing action because temperatures were maintained slightly below the SR limit.

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Page 16 of 24

Attachment 1 Evaluation of Proposed Changes Peak UHS temperatures from July 6, 2012 to July 9, 2012 existed for a period of-72 hours before lowering due to natural cooling (Figure 3). The July 2012 peak temperatures resulted in an approved Notice of Enforcement Discretion (NOED) (ADAMS Access No. ML12194A681 ).

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Page 17 of 24

Attachment 1 Evaluation of Proposed Changes Peak UHS temperatures from July 6, 2020 to July 9, 2020 existed for a period of -72 hours before lowering due to natural cooling (Figure 4 ). The July 2020 peak temperatures were slightly greater in magnitude than the July 2012 period. The higher temperatures at the onset of July 2020 prompted EGC to apply for a LAR to raise the SR limit to 102.8°F. The license amendment was issued for Braidwood on September 24, 2020 (ADAMS Accession No. ML20245E419).

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• ess SW PUt. p IA DISCH HORT . SX-TI-SX015 s:ss SN P<'. "28 DISCH DR T SX-TI-SX016 Based on historical trends it can be concluded that there is a reasonable potential for future peak temperature periods to be of at least similar or greater magnitude and occur for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or greater. The 7 day completion time , in conjunction with more frequent monitoring, provides adequate time period to allow for natural cooling to return UHS temperatures to within SR 3.7.9.2. The proposed Completion Time does not involve a change to the design or method of operation of the UHS.

During the 7 days period, new Required Action A.1.1 will limit the maximum UHS temperature to the value that has been evaluated to ensure that the Braidwood Station current licensing basis analyses and evaluations continue to be met during this time. The current average UHS water temperature limit is 102°F. Braidwood Station previously received a temporary increase of UHS water temperature limit to 102.8 °F as documented in NRC SER dated July 13, 2021 (ADAMS Access No . ML21154A046) , and as discussed in this submittal, margins exist to support higher UHS temperatures.

Page 18 of 24

Attachment 1 Evaluation of Proposed Changes

4.0 REGULATORY EVALUATION

4.1 APPLICABLE REGULATORY REQUIREMENTS/CRITERIA 10 CFR 50.36, "Technical Specifications," paragraph (c)(2)(i) states that limiting conditions for operation are the lowest functional capability or performance level of equipment required for safe operation of the facility, and when a limiting condition for operation is not met, the licensee shall shut down the reactor or follow any remedial actions permitted by the TS until the condition can be met.

The proposed changes to the Required Action and associated Completion Time for Condition A ,

to return the UHS average temperature to within the TS limit, and the change to Condition B if the Required Action and associated Completion Time for Condition A are not met, comply with the requirement to follow a remedial action to return the limit to meet the limiting condition for operation or shut the unit down.

The design of the UHS satisfies the requirements of 10 CFR 50.36(c)(2)(ii), Criterion 3. This criterion states the following :

(ii) A Technical Specification Limiting Condition for Operation (TS LCO) of a nuclear reactor must be established for each item meeting one or more of the following criteria:

Criterion 3. A structure, system, or component that is part of the primary success path and which functions or actuates to mitigate a design basis accident or transient that either assumes the failure of or presents a challenge to the integrity of a fission product barrier.

The proposed change does not change the design function or purpose of the UHS, therefore, Criterion 3 of 10 CFR 50.36(c)(2)(ii) continues to be met.

General Design Criteria 2, "Design bases for protection against natural phenomena," and General Design Criteria 44, "Cooling water," of Appendix A to 10 CFR Part 50, "General Design Criteria for Nuclear Power Plants," provides design considerations for the UHS. RG 1.27, "Ultimate Heat Sink for Nuclear Power Plants," Revision 2, dated January 1976, provides an acceptable approach for satisfying General Design Criteria 2 and 44. The guidance contained in RG 1.27 , Revision 2, was utilized for the temperature analysis of the Braidwood Station UHS .

General Design Criteria 5, "Sharing of structures, systems and components ," of Appendix A to 10 CFR Part 50 also provides design criteria applicable to the UHS, a shared system between Braidwood Station Units 1 and 2. The current analysis of the UHS OBA, was evaluated consistent with the current methodology which considers a OBA event (i .e., a LOCA with LOOP) along with the safe non-accident shutdown and cooldown of the opposite unit. The proposed changes do not impact the current analysis, therefore, General Design Criterion 5 continues to be met by the evaluation of the UHS OBA at an increased initial UHS temperature .

The proposed changes continue to ensure that the plant's safety related equipment will maintain its design function at a higher UHS temperature. Therefore, there is no adverse impact of this change on the Braidwood Station licensing basis.

Page 19 of 24

Attachment 1 Evaluation of Proposed Changes 4.2 NO SIGNIFICANT HAZARDS CONSIDERATION DETERMINATION In accordance with 10 CFR 50.90, "Application for amendment of license, construction permit, or early site permit," Exelon Generation Company, LLC (EGC) is requesting a change to the Technical Specifications (TS) of Renewed Facility Operating License Nos. NPF-72 and NPF-77 for Braidwood Station, Units 1 and 2.

The Ultimate Heat Sink (UHS) for Braidwood Station, Units 1 and 2 provides a heat sink for processing and operating heat from safety related components during a transient or accident, as well as during normal operation. This is done by utilizing the Essential Service Water (SX)

System and the Component Cooling Water (CC) system. The UHS consists of an excavated essential cooling pond integral with the main cooling pond . The volume of the excavated essential cooling pond is sized to permit the safe shutdown and cooldown of both Braidwood Station units for a 30 day period, including a design basis event with no additional makeup water source. As discussed in the Braidwood Station Updated Final Safety Analysis Report (UFSAR), the design basis event for the Braidwood Station UHS is a Loss of Coolant Accident (LOCA) coincident with a Loss of Offsite Power (LOOP) in one unit, in conjunction with a normal shutdown of the other unit. The UHS provides a heat sink for process and operating heat from safety-related components during the UHS design basis event.

The proposed amendment revises Technical Specification (TS) 3.7.9 Required Actions A.1, and A.2, to be in Mode 3 and Mode 5, and their associated Completion Times of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> to be Required Actions A.2.1 and A.2.2.

Aa new Required Action A.1.1, "Verify UHS temperature at or below the maximum analyzed temperature limit," with a Completion Time of "Immediately" and "Once every 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> thereafter" to the current Condition A, which states: "UHS inoperable due to average water temperature."

This new Required Action provides additional monitoring during which Operations would monitor and trend diurnal cooling effects of the lake until SR 3.7.9.2 is met.

A new Required Action A.1.2, "Verify UHS average water temperature within SR 3.7.9.2." with a Completion Time of 7 days is added to current Condition A, which states: "UHS inoperable due to average water temperature."

The proposed amendment also revises TS Surveillance Requirement (SR) 3.7.9.2 to delete the text:

"::::; 102.8°F until September 30, 2021. After September 30, 2021, verify average water temperature of UHS is."

The evaluations and analyses that will be performed to support the proposed license amendment demonstrate that the plant's safety related equipment will maintain its design function at a higher UHS temperature.

According to 10 CFR 50.92, "Issuance of amendment," paragraph (c), a proposed amendment to an operating license involves no significant hazards consideration if operation of the facility in accordance with the proposed amendment would not:

Page 20 of 24

Attachment 1 Evaluation of Proposed Changes

1) Involve a significant increase in the probability or consequences of an accident previously evaluated;

2) Create the possibility of a new or different kind of accident from any accident previously evaluated ; or

3) Involve a significant reduction in a margin of safety.

In support of this determination , an evaluation of each of the three criteria set forth in 10 CFR 50.92 is provided below:

1. Does the Proposed Change Involve a Significant Increase in the Probability or Consequences of an Accident Previously Evaluated?

Response: No The likelihood of a malfunction of any systems, structures or components (SSCs) supported by the Ultimate Heat Sink (UHS) is not significantly increased by an increased UHS temperature because the evaluation and analyses that will be performed will confirm that the licensing basis analyses continue to be met. The UHS provides a heat sink for process and operating heat from safety related components during a transient or accident, as well as during normal operation. The proposed change does not make any physical changes to any plant SSCs, nor does it alter any of the assumptions or conditions upon which the UHS is designed. The UHS is not an initiator of any analyzed accident. All equipment supported by the UHS has been evaluated to demonstrate that their performance and operation remains as described in the UFSAR with no increase in probability of failure or malfunction .

The SSCs credited to mitigate the consequences of postulated design basis accidents remain capable of performing their design basis function . The increased UHS temperature will be evaluated using the UFSAR described methods to demonstrate that the UHS remains capable of removing normal operating and post-accident heat. The increased UHS temperature and resulting containment response following a postulated design basis accident will be demonstrated to not be impacted. Additionally, all the UHS supported equipment, credited in the accident analysis to mitigate an accident, will be shown to continue to perform their design function as described in the UFSAR.

Therefore, the proposed change does not involve a significant increase in the probability or consequences of an accident previously evaluated .

2. Does the Proposed Change Create the Possibility of a New or Different Kind of Accident from any Accident Previously Evaluated?

Response: No The proposed change does not create the possibility of a new or different kind of accident from any accident previously evaluated . The proposed change does not introduce any new modes of plant operation, change the design function of any SSC, or change the mode of operation of any SSC. There are no new equipment failure modes or malfunctions created as affected SSCs continue to operate in the same manner as previously evaluated and will be evaluated to perform as designed at an increased UHS temperature, as assumed in the safety analysis.

Page 21 of 24

Attachment 1 Evaluation of Proposed Changes Additionally, the accident initiators discussed in the UFSAR are not impacted, and no new accident initiators are postulated as a result of an increased UHS temperature.

Therefore, the proposed change does not create the possibility of a new or different kind of accident from any previously evaluated.

3. Does the Proposed Change Involve a Significant Reduction in a Margin of Safety?

Response : No The proposed change continues to ensure that the maximum temperature of the cooling water supplied to the plant SSCs during a UHS design basis event remains within the evaluated equipment limits and capabilities assumed in the accident analysis. The proposed change does not result in any changes to the function of any plant equipment, including setpoints and automatic actuations. All equipment will function as designed in the plant safety analysis without any physical modifications. The proposed change does not alter a limiting condition for operation, limiting safety system setting, or safety limit specified in the Technical Specifications.

The proposed change does not adversely impact the UHS inventory required to be available for the UFSAR described design basis accident involving the worst case 30-day period including losses for evaporation and seepage to support safe shutdown and cooldown of both Braidwood Station units. Additionally, the structural integrity of the UHS is not impacted and remains acceptable after the change, thereby ensuring that the assumptions for both UHS temperature and inventory remain valid.

Therefore, since there is no adverse impact of this proposed change on the Braidwood Station safety analysis, there is no reduction in the margin of safety of the plant.

4.3 CONCLUSION

S In conclusion, based on the considerations discussed above, (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.

5.0 ENVIRONMENTAL CONSIDERATION

EGC has evaluated this proposed operating license amendment consistent with the criteria for identification of licensing and regulatory actions requiring environmental assessment in accordance with 10 CFR 51 .21, "Criteria for and identification of licensing and regulatory actions requiring environmental assessments." EGC has determined that this proposed change meets the criteria for a categorical exclusion set forth in paragraph (c)(9) of 10 CFR 51.22, "Criterion or categorical exclusion; identification of licensing and regulatory actions eligible for categorical exclusion or otherwise not requiring environmental review," and as such , has determined that no irreversible consequences exist in accordance with paragraph (b) of 10 CFR 50.92, "Issuance of amendment." This determination is based on the fact that this change is being proposed as an amendment to the license issued pursuant to 10 CFR 50, "Domestic Licensing of Production and Utilization Facilities," which changes a requirement with respect to installation or use of a Page 22 of 24

Attachment 1 Evaluation of Proposed Changes facility component located within the restricted area, as defined in 10 CFR 20, "Standards for Protection Against Radiation," or which changes an inspection or a surveillance requirement, and the amendment meets the following specific criteria:

(i) The amendment involves no significant hazards consideration.

As demonstrated in Section 4.2, "No Significant Hazards Consideration," the proposed change does not involve any significant hazards consideration .

(ii) There is no significant change in the types or significant increase in the amounts of any effluent that may be released offsite.

The proposed change does not result in an increase in power level, does not increase the production nor alter the flow path or method of disposal of radioactive waste or byproducts. The proposed change continues to ensure that the plant's safety related equipment will maintain its design function at a higher UHS temperature. Therefore, there is no impact of this change on Braidwood Station safety analyses including the consequences of such events.

Based on the above evaluation , the proposed change will not result in a significant change in the types or significant increase in the amounts of any effluent released offsite.

(iii) There is no significant increase in individual or cumulative occupational radiation exposure.

There is no net increase in individual or cumulative occupational radiation exposure due to the proposed change. The proposed action will not change the level of controls or methodology used for processing of radioactive effluents or handling of solid radioactive waste , nor will the proposed action result in any change in the normal radiation levels within the plant.

Based on the above information, there will be no increase in individual or cumulative occupational radiation exposure resulting from this change.

6.0 REFERENCES

1. NRC Safety Evaluation Report, Braidwood Station Units 1 and 2 - Issuance of Amendments RE: Ultimate Heat Sink Temperature Increase, dated July 26, 2016.

(ADAMS Accession No. ML16133A438)

2. WCAP-10325-P-A, "Westinghouse LOCA Mass and Energy Release Model for Containment Design March 1979 Version," dated May 1983.

3. Letter from D. Murray (Exelon Generation Company, LLC) to U.S. Nuclear Regulatory Commission, "License Amendment to Braidwood Station , Units 1 and 2, Technical Specification 3.7.9, 'Ultimate Heat Sink,"' dated July 15, 2020 (ADAMS Accession No. ML20197A434 ).

4. Response to Request for Additional Information Regarding License Amendment to Braidwood Station, Units 1 and 2, Technical Specification 3.7.9, "Ultimate Heat Sink,"

dated August 14, 2020 (ADAMS Accession No. ML20227A375)

Page 23 of 24

Attachment 1 Evaluation of Proposed Changes

5. NRC Safety Evaluation Report, Braidwood Station, Units 1 and 2 - Issuance of Amendments Nos. 218 and 218 Re: Revision of Technical Specifications for the Ultimate Heat Sink, (EPID L-2020-LLA-0159), dated September 24, 2020 (ADAMS Accession No. ML20245E419).

6. Letter from D. Murray (Exelon Generation Company, LLC) to U.S. Nuclear Regulatory Commission, "License Amendment to Braidwood Station , Units 1 and 2, Technical Specification 3.7.9, 'Ultimate Heat Sink,"' dated May 27, 2021 (ADAMS Accession No. ML32258A543) .

7. NRC Safety Evaluation Report Braidwood Station , Units 1 and 2 - Issuance of Amendments Nos. 222 and 222 Re: Revision of Technical Specifications for the Ultimate Heat Sink, (EPID L-2021-LLA-0095), dated July 13, 2021 (ADAMS Accession No. ML21154A046).

8. NRC Safety Evaluation Report, Braidwood Station, Units 1 and 2, and Byron Station ,

Units 1 and 2 - Issuance of Amendments Nos. 219, 219, 223, and 223 Re: Revision of Technical Specifications 5.6.5, "Core Operating Limits Report (COLR)", (EPID L-2020-LLA-0038), dated December 28, 2020 (ADAMS Accession No. ML20315A516)

9. Engineering Change (EC) Evaluation 632041, Revision 0, "Support Analyses for the License Amendment Request to Raise the Maximum UHS Temperature for the UHS in TS LCO 3.7.9."

10. Design Analysis CN-CRA-10-54 Revision 2, "Braidwood Units 1 and 2 - LOCA Mass and Energy Release and Containment Integrity Analyses to Support an Increase in the Lake Temperature"

11. Design Analysis CN-CRA-13-29 Revision 0, "Byron and Braidwood Units 1: Steamline Break Mass and Energy Releases Inside Containment"

12. Design Analysis CN-CRA-13-26 Revision 0, "Byron and Braidwood Units 2: Steamline Break Mass Containment Response Analysis"

13. UFSAR Section 6.2 Page 24 of 24

ATTACHMENT 2 BRAIDWOOD STATION UNITS 1and2 Renewed Facility Operting License Nos. NPF-72 and NPF-77 Docket Nos. STN-50-456 and STN-50-457 Markup of Technical Specifications Pages 3.7.9-1 3.7.9-2

3.7 PLANT SYSTEMS 3.7.9 Ultima t e Heat Sink (UHS)

LCD 3.7.9 The UHS shall be OPERABLE.

APPLICABILITY: MODES 1, 2, 3, and 4.

ACTIONS CONDITION REQUIRED ACTION COMPLETION TIME A. UHS inoperable due to A.1.1 Verify UHS average Immediately average water water temperature at temperature. or below the maximum analyzed temperature limit.

AND Once per 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> thereafter AND A.1.2 Verify UHS average 7 Days water temperature within SR 3.7.9.2.

OR A. 2.1-+/- Be in MODE 3. 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> AND A. 2.2~ Be in MODE 5. 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> B. UHS inoperable for B.1 Be in MODE 3. 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> reasons other than Condition A. AND B.2 Be in MODE 5. 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> BRAIDWOOD - UNITS 1 &2 3.7.9 - 1 Amendment m

SURVEILLANCE REQUIREMENTS SURVEILLANCE FREQUENCY SR 3.7.9.1 Verify water level of UHS is~ 590 ft Mean In accordance Sea Level (MSU. with the Surveillance Frequency Control Program SR 3.7.9.2 Verify average water temperature of UHS is In accordance

<102.8°F until September 30, 2021. After with the September 30, 2021, verify average \Jater Surveillance temperature of U~S is < 102°F. Frequency Control Program SR 3.7.9.3 Verify UHS contains a water volume of In accordance

~ 555.8 acre-feet with the Surveillance Frequency Control Program BRAIDWOOD - UNITS 1 &2 3.7.9 - 2 Amendment m

ATTACHMENT 3 BRAIDWOOD STATION UNITS 1and2 Renewed Facility Operting License Nos. NPF-72 and NPF-77 Docket Nos. STN-50-456 and STN-50-457 Markup of Technical Specifications Bases Page B 3.7.9-1 B 3.7.9-2 B 3.7.9-3 B 3.7.9-4 (For Information Only)

UHS B 3.7.9 B 3.7 PLANT SYSTEMS B 3.7.9 Ultimate Heat Sink CUHS)

BASES BACKGROUND The UHS provides a heat sink for processing and operating heat from safety related components during a transient or accident, as well as during normal operation. This is done by utilizing the Essential Service Water CSX) System and the Component Cooling Water CCC) System.

The UHS consists of an excavated essential cooling pond integral with the main cooling pond, and the piping and valves connecting the pond with the SX System pumps. The UHS is described in UFSAR, Section 9.2.5 (Ref. 1). The two principal functions of the UHS are t he dissipat ion of residual heat after reactor shutdown, and dissipation of residual heat after an accident.

The basic performance requirements are that a 30 day supply of water be available, and that the design basis temperatures of safety related equipment not be exceeded.

The UHS is sufficiently oversized to permit a minimum of 30 days of operation with no makeup.

Additional information on the design and opera t ion of the system, along with a list of components served, can be found in Reference 1.

BRAIDWOOD - UNITS 1 &2 B 3.7.9 - 1 Revision 0

UHS B 3.7.9 BASES APPLICABLE The UHS is the sink for heat removed from the reactor core SAFETY ANALYSES following all accidents and anticipated operational occurrences in which the unit is cooled down and placed on Residual Heat Removal CRHR) operation. The UHS is also the normal heat sink for condenser cooling via the Circulating Water System. Unit operation at full power represents the UHS maximum heat load. Its maximum post accident heat load occurs 20 minutes after a design basis Loss Of Coolant Accident CLOCA). Near this time, the unit swi t ches from injection to recirculation and the containment cooling systems and RHR are required to remove the core decay heat.

The operating limits are based on conservative heat transfer analyses for the worst case LOCA. Reference 1 provides the details of the assumptions used in t he analysis, which include worst expected meteorological conditions, conservative uncertainties when calculating decay heat, and worst case single failure (e.g., single failure of a manmade structure). The UHS is designed in accordance with Regulatory Guide 1.27 (Ref. 2), which requires a 30 day supply of cooling water in the UHS.

The UHS satisfies Criterion 3 of 10 CFR 50.36(c)(2)(ii).

LCD The UHS is required to be OPERABLE and is considered OPERABLE if it contains a sufficient volume of water at or below the maximum temperature that would allow the SX System to operate for at least 30 days following the design basis LOCA without the loss of Net Positive Suction Head CNPSH),

and without exceeding the maximum design temperature of the equipment served by the SX System. To meet this condition, the UHS temperature should not exceed 102°F (102.8°~ until September 30, 2021) and the level should not fall below 590 ft mean sea level during normal unit opera t ion.

APPLICABILITY In MODES 1, 2, 3, and 4, the UHS is required to support the OPERABILITY of the equipment serviced by the UHS and required to be OPERABLE in these MODES.

In MODE 5 or 6, the OPERABILITY requirements of the UHS are determined by the systems it support s.

BRAIDWOOD - UNITS 1 &2 B 3.7.9 - 2 Revision -+/-J7

UHS B 3.7.9 BASES ACTIONS If the average UHS water temperature is not within SR 3.7.9.2, an evaluation of the affected safety analyses and other evaluations must be performed to determine that the applicable acceptance criteria will continue to be met during the Design Basis Event for the duration of the operation under this condition. The safety analyses discussed in FSAR Chapters 6 and 15 that may be adversely affected will be evaluated to ensure that the analysis results remain valid for the duration of continued operation under this condition.

The Completion Time of Immediately allows for the use of margin tradeoff from evaluations already completed to ensure that the analysis results remain valid for the duration of continued operation under this condition. Additionally, a Completion Time of "Once per 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> thereafter" will ensure that local precision monitoring of the UHS temperature occurs so that Operations can trend the diurnal cooling effects on the lake until SR 3.7.9.2 is met.

The Completion Time of 7 days also provides sufficient time to allow the natural diurnal cooling behavior of the lake to occur to return the average UHS temperature to within SR 3.7.9.2.

A. 2.lJ and A. 2.2~

If the UHS is inoperable due to average water t emperature, the unit must be placed in a MODE in which the LCD does not apply. To achieve this status , the unit must be placed in at least MODE 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and in MODE 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.

B.l and B.2 If the UHS is inoperable for reasons other than Condition A, the unit must be placed in a MODE in which the LCD does not apply. To achieve this status , the unit must be placed in at least MODE 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in MODE 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.

The allowed Completion Times are reasonable, based on operating experience, to reach the required unit conditions from full power conditions in an orderly manner and without challenging plant systems.

BRAIDWOOD - UNITS 1 &2 B 3.7.9 - 3 Revision ~

UHS B 3.7.9 BASES SURVEILLANCE SR 3.7.9.1 REQUIREMENTS This SR verifies that adequate long term (30 day) cooling can be maintained. The specified level also ensures that sufficient NPSH is available to operate the SX pumps. The Surveillance Frequency is controlled under the Surveillance Frequency Control Program. This SR verifies that the UHS water level is~ 590 ft mean sea level United States Geological Society datum.

SR 3.7.9.2 This SR verifies that the SX System is available to cool the CC System to at least its maximum design temperature with the maximum accident or normal design heat loads for 30 days following a Design Basis Accident. This SR verifies that the average water temperature of the UHS is~ 102°F (102.8°P until September 30, 2021) , as measured at the discharge of an SX pump. The Surveillance Frequency is cont rolled under the Surveillance Frequency Control Program.

SR 3.7.9 .3 This surveillance verifies that the UHS contains adequate storage volume to supply the required design basis inventory to support the function of the essential service water system. SR 3.7.9.1 verifies the contained volume of the UHS, while this SR verifies that the UHS, if filled to the depth required by SR 3.7.9.1, can supply the water required to support the safety function of the system.

SR 3.7.9.3 assures that the volume of the UHS is greater than or equal to 555.8 acre-feet This surveillance is performed by means of a hydrographic survey. The Surveillance Frequency is controlled under the Surveillance Frequency Control Program.

REFERENCES 1. UFSAR, Section 9.2.5.

2. Regulatory Guide 1.27.

BRAIDWOOD - UNITS 1 &2 B 3.7.9 - 4 Revision -+/-i9

ATTACHMENT 4 BRAIDWOOD STATION UNITS 1and2 Renewed Facility Operting License Nos. NPF-72 and NPF-77 Docket Nos. STN-50-456 and STN-50-457 Revised Clean Technical Specifications Pages 3.7.9-1 3.7.9-2

3.7 PLANT SYSTEMS 3.7.9 Ultima t e Heat Sink (UHS)

LCD 3.7.9 The UHS shall be OPERABLE.

APPLICABILITY: MODES 1, 2, 3, and 4.

ACTIONS CONDITION REQUIRED ACTION COMPLETION TIME A. UHS inoperable due to A.1.1 Verify UHS average Immediately average water water temperature at temperature. or below the maximum analyzed temperature limit.

AND Once per 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> thereafter AND A.1.2 Verify UHS average 7 Days water temperature within SR 3.7.9.2.

OR A.2.1 Be in MODE 3. 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> AND A.2.2 Be in MODE 5. 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> B. UHS inoperable for B.1 Be in MODE 3. 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> reasons other than Condition A. AND B.2 Be in MODE 5. 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> BRAIDWOOD - UNITS 1 &2 3.7.9 - 1 Amendment

SURVEILLANCE REQUIREMENTS SURVEILLANCE FREQUENCY SR 3.7.9.1 Verify water level of UHS is~ 590 ft Mean In accordance Sea Level (MSU. with the Surveillance Frequency Control Program SR 3.7.9.2 Verify average water temperature of UHS is In accordance s 102°F. with the Surveillance Frequency Control Program SR 3.7.9.3 Verify UHS contains a water volume of In accordance

~ 555.8 acre-feet with the Surveillance Frequency Control Program BRAIDWOOD - UNITS 1 &2 3.7.9 - 2 Amendment