ML23313A043

Summary of Regulatory Audit in Support of Amendment Request for Control Room Air Conditioning Technical Specifications

ML23313A043
Person / Time
Site:	Limerick
Issue date:	11/13/2023
From:	Audrey Klett Plant Licensing Branch 1
To:	Rhoades D Constellation Energy Generation
Sreenivas V, NRR/DORL/LPLI, 415-2597
References
EPID L-2022-LLA-0174
Download: ML23313A043 (10)

Text

November 13, 2023 Mr. David P. Rhoades Senior Vice President Constellation Energy Generation, LLC President and Chief Nuclear Officer Constellation Nuclear 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

LIMERICK GENERATING STATION, UNITS 1 AND 2 -

SUMMARY

OF REGULATORY AUDIT IN SUPPORT OF AMENDMENT REQUEST FOR CONTROL ROOM AIR CONDITIONING TECHNICAL SPECIFICATIONS (EPID L-2022-LLA-0174)

Dear Mr. Rhoades:

By letter dated November 17, 2022, as supplemented by letters dated August 30, and October 31, 2023 (Agencywide Documents Access and Management System Accession (ADAMS) Nos. ML22321A105, ML23242A217, and ML23304A190, respectively), Constellation Energy Generation, LLC, (the licensee) submitted a license amendment request (LAR) for Limerick Generating Station, Units 1 and 2 (Limerick).1 The licensee requested to revise the technical specifications for the control room air conditioning systems.

The U.S. Nuclear Regulatory Commission (NRC) staff conducted a virtual audit to support its review of the LAR. The NRC staff reviewed information and interviewed licensee staff. The NRC staff issued its audit plan on July 27, 2023 (ML23208A194). Enclosure 1 of this audit summary lists the individuals that took part in or attended the audit. Enclosure 2 lists the NRC staffs audit questions.

The NRC staff conducted the audit using virtual meetings and an Internet-based portal provided by the licensee. Using the licensees portal, the NRC staff reviewed information related to the LAR but not available on the Limerick dockets. During the audit, the staff also met virtually with the licensee on August 21, 2023. The staff used this meeting to confirm its understanding of the LAR, discuss the information in the portal, and decide whether the NRC staff identified any information that needs to be submitted on the docket to complete the staffs safety evaluation.

During the audit, the staff and the licensee discussed the audit questions in enclosure 2, and the staff identified information it needed on the docket to support its review. After the audit discussions, the NRC sent the licensee a request for additional information on October 3, 2023 (ML23276B464). The licensee responded to this request on October 31, 2023 (ML23304A190).

1 Renewed Facility Operating License Nos. NPF 39 and NPF 85, respectively

The NRCs licensing project manager informed licensee staff by telephone on November 8, 2023, that the NRC staff had completed its audit. There were no open items resulting from the audit.

If you have any questions, please contact me at (301) 415-0489 or by email to Audrey.Klett@nrc.gov.

Sincerely,

/RA/

Audrey L. Klett, Senior Project Manager Plant Licensing Branch I Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-352 and 50-353

Enclosures:

1. List of Audit Participants

2. List of Audited Documents cc: Listserv

List of Audit Participants U.S. Nuclear Regulatory Commission Licensee1 Staff Alferink, Steven (NRR2/DRA3/APLC4)

Berg, James Cruz-Rosado, Luis (NRR/DORL5/LPL16)

Curtin, Gregory Edwards, Theo (NRR/DORL/LPL1)

Flickinger, Stephen Karipineni, Nageswara (NRR/DSS7/SCPB8)

Swoyer, Todd Ki, DaBin (NRR/DRO9/IOLB10)

Klett, Audrey (NRR/DORL/LPL1)

Wilson, Joshua (NRR/DSS/STSB11)

Wyman, Steve (NRR/DEX12/EEEB13) 1 Constellation Energy Generation, LLC 2 Office of Nuclear Reactor Regulation 3 Division of Risk Assessment 4 PRA Licensing Branch C 5 Division of Operating Reactor Licensing 6 Plant Licensing Branch 1 7 Division of Safety Systems 8 Containment and Plant Systems Branch 9 Division of Reactor Oversight 10 Operator Licensing and Human Factors Branch 11 Technical Specifications Branch 12 Division of Engineering and External Hazards 13 Electrical Engineering Branch

List of Audit Questions During its review of the license amendment request (LAR) for the Limerick Generating Station, Units 1 and 2 (Limerick), the U.S. Nuclear Regulatory Commission (NRC) staff provided the licensee with the following questions and audited the licensees responses that the licensee posted on its internet-based portal.

Item No.

Audit Request 1

Clarification of which supplementary cooling provisions discussed in the LAR that are beyond the scope of TSTF-477 [Technical Specifications Task Force Traveler 477], Revision 3, that the licensee is requesting NRC staff review and approval 2

High level description of the control enclosure and the control envelope (including elevations and major equipment in each), supported by sketches and/or drawings showing the doors leading from the turbine enclosure to the control enclosure and control envelope, including confirmation of whether the doors are qualified to withstand high energy line break (HELB) 3 Description of the temporary chiller water hoses (jumpers) proximity to the control room (including a description of where the jumper will be located and routed from the turbine enclosure to the control enclosure) and available monitoring to identify the onset of a HELB in the turbine enclosure 4

Description of the ability of operators to close the HELB door between the turbine enclosure and control enclosure during a HELB event in the turbine enclosure 5

Description of the consequences to the control enclosure and its operability (including whether control room habitability is affected) if there is a HELB or if the temporary chiller water hose (jumper) breaks 6

Description of how the plant would be brought to a safe shutdown condition if a HELB occurs during the proposed jumper supplementary cooling provision (e.g.,

operators ability to detect and respond to a HELB) 7 High level description of factors that make a catastrophic pipe failure in the turbine building unlikely in the plant configuration requested in the LAR 8

Description of the ability of operators or a leakage detection system to detect leakage in the turbine enclosure prior to a HELB (including the leak rates that may be detected) 9 Description of the actions operators would take if leakage was detected in the turbine enclosure prior to a HELB 10 Does the licensee have an estimate of the likelihood of a HELB occurring (e.g., an order-of-magnitude estimate for the frequency, not a specific/detailed PRA [probabilistic risk assessment] analysis) during this timeframe?

11 What is the size of the turbine building fan vent room (or whichever room in the turbine enclosure is of concern for a HELB during the LCO [limiting condition for operation]), and provide any information on increase in temperature, humidity, radiation, etc., that would be experienced in this room if a small leak were to occur.

12 Audit response No. 6 indicates that a potential HELB event with the door propped open is bounded by the fire analysis for fire area 27, which assumes the complete loss of equipment in this fire area. Please confirm whether the fire safe shutdown in this area relies on an alternative shutdown (e.g., confirm whether a safe shutdown can be performed from the control room) or any equipment in the turbine enclosure that could be affected by a HELB.

13 Regarding audit items 1 and 3 responses:

a. Regarding the components in room 619, what are the limiting components at the elevated temperature environment, and are any of them are safety related and required for safe shutdown?

b. Are any doors to other rooms kept open to facilitate the routing of the jumpers?

c. Are the rooms along the path of the jumpers to the control room HVAC

[heating, ventilation, and air conditioning] cooling coils served by any cooling systems?

d. What safety related equipment is in those rooms, and how are the temperatures determined in those rooms during the 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />?

e. Has Constellation already implemented a power rerate and MUR

[measurement uncertainty recapture uprate] at Limerick? What is their significance in the licensees audit response (e.g., what scenario leads to the 135 °F temperature discussed in the response)?

14 Regarding audit item 2 response:

f. Please confirm the elevation of the main control room.

g. Please confirm the level containing all the control room related HVAC (e.g., cooling trains (filters, coils, fans, etc.) and the control room emergency filter trains). In addition, please also confirm whether which level houses other HVAC equipment unrelated to control room. Please confirm which level also contains room 619. Please confirm the levels on which the control room HVAC ductwork travels.

h. Please confirm the level of the control building chillers.

i. Please confirm whether, in addition to control room HVAC, the chillers also support other HVAC equipment (e.g., battery rooms). When the chillers are not operating, how are the non-control room HVAC systems supported?

15 Regarding audit item 5 response:

j. Similar to question [13] above about impact on the rooms along the path of the jumpers, does the control room habitability envelope include control room cooling equipment, safety related filters, etc. located in the same room?

Please confirm whether a HELB impact would propagate to this room and, if it did, what measures would be needed to address the temperature and habitability?

k. Regarding page 8 of 17 (2nd paragraph) of the licensees audit response, confirm whether a dual unit shutdown starts as soon as the control room technical specification (TS) temperature limit is exceeded, given that this limit could be exceeded before the 72-hour LCO expiration.

l. Regarding page 9 of 17 (last paragraph) of the licensees audit response, confirm whether, if the dry well temperature exceeded the TS limit, Unit 1 would be shut down and Unit 2 would continue to operate until the expiration of the 72-hour LCO, provided the control room temperature is maintained within the TS acceptance level using chiller water from Unit 1 drywell chiller.

16 Regarding audit item 9 response, would station procedures highlight to operators why certain actions (e.g., leak detection, watches pertaining to the open door to the control enclosure building) are required during the 72-hour LCO?

17 Section 3.5 of the LAR [attachment 1] states that the proposed footnote is based, in part, on the low probability of the occurrence of events which would potentially challenge MCR habitability and safety related equipment functionality temperature limits.

Section 3.5.2 of the LAR [attachment 1] states that the 72-hour condition applicable to loss of normal main control room cooling is based, in part, on the low probability of the occurrence of concurrent postulated events while in TS LCO 3.7.2.2 action a.2. Section 3.5.2 of the LAR [attachment 1] also states that the installation and use of these temporary jumpers with the non-safety related non-diesel backed drywell chilled water system as another temporary supplemental cooling method assumes that no other concurrent postulated plant accidents, severe natural phenomenon, or other events occur when in this short duration action statement on the basis of low probability. Finally, section 3.5.2 of the LAR states that having multiple concurrent failures while in TS LCO 3.7.2.2 action a.2 meets the low probability threshold and therefore temporary crosstie supply and return jumper installation is considered acceptable, as a viable nonpreferred temporary supplemental cooling source (emphasis added).

The licensees responses to audit questions 5 and 6 state that a HELB was not evaluated by the LAR and is outside the scope of the submittal because the justification provided in the LAR did not require postulating a HELB and its associated consequences with the HELB door blocked partially open while in the dual unit 72-hour complete loss of cooling LCO.

The probability of events occurring that would require control room isolation is discussed in TSTF-477. Section 4.0 states that the 72-hour completion time is reasonable considering that control room temperature is being maintained within limits and the low probability of an event occurring that would require control room isolation. Section 5.1 also states that the 72-hour completion time to restore one control room AC subsystem will not cause a significant reduction in the margin of safety considering that control room temperature is being maintained within limits, the low probability of an event occurring that would require control room isolation, and the availability of alternate cooling methods.

The proposed edits to the basis for TS 3.7.5/3.7.4 also state that the 72-hour completion time is reasonable considering that the control room temperature is being maintained within limits and the low probability of an event occurring requiring control room isolation.

The statements in TSTF-477 indicate that the proposed completion time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> is acceptable based, in part, on the low probability of occurrence of events that would require control room isolation. It is unclear to the staff how these statements support the assertion that a HELB event is outside the scope of the submittal.

1. How do the statements in TSTF-477 regarding the low probability of events that would require control room isolation support the assertion that a HELB event is outside the scope of the submittal?

2. The statements in section 3.5.2 of the LAR [attachment 1] add the word concurrent when discussing the low probability of events that would require control room isolation. Is the word concurrent intended to refer to the occurrence of a HELB while in TS LCO 3.7.2.2 action a.2, the occurrence of a HELB and another design basis event simultaneously while in TS LCO 3.7.2.2 action, or something else?

18 In response to audit question 2, the licensee stated that the Limerick HELB design basis postulates a hypothetical guillotine type line break, isolate it via an isolation valve or reactor scram, cope with its associated environmental conditions, and achieve plant safe shutdown. The licensee also stated that the hypothetical turbine enclosure HELB worst case vulnerabilities are a main steam system steam break of a 26 [inch] pipe and a feedwater system high energy liquid break of either a 20 or 34 pipe.

The plant response to a feedwater line break outside primary containment is described in the UFSAR [Updated Final Safety Analysis Report], section 15.6.6.

Section 15.6.6.2.2 includes the following statements:

It is assumed that the normally operating plant instrumentation and controls are functioning. Credit is taken for the actuation of the reactor isolation system and ECCS [emergency core cooling system]. The RPS [reactor protection system] (MSRVs [main steam relief valves], ECCS, and CRD [control rod drives]) and plant protection system (RHR [residual heat removal] heat exchangers) are assumed to function properly to assure a safe shutdown.

The ESF [engineered safeguard features] and RCIC/HPCI

[reactor core isolation cooling/high pressure coolant injection]

systems are assumed to operate normally.

Section 15.6.6.2.3 states that a feedwater line break outside primary containment can be isolated and either the RCIC or HPCI can provide adequate flow to the vessel to maintain core cooling and prevent fuel clad failure. This section also states that a single failure of either the HPCI or the RCIC would still provide sufficient flow to keep the core covered with water.

Regulatory Issue Summary (RIS)01-009 provides guidance on the control of hazard barriers. The RIS states that a hazard barrier may be removed on a temporary basis to facilitate plant maintenance, the implementation of a design change, or the implementation of compensatory measures to address degraded or nonconforming conditions. The RIS also states that other considerations, such as the administrative provisions for controlling fire barriers and the plant TS, may place limitations on continued reactor operation with a hazard barrier removed.

The RIS provides an example of an auxiliary feedwater (AFW) pump that is credited with mitigating a HELB event, which would be rendered inoperable if a barrier that is credited with protecting the AFW pump from the effects of the postulated HELB event is removed to allow maintenance to be performed in the AFW pump room. For this example, the RIS states that the AFW pump would not be able to mitigate the HELB event with the barrier removed and, consistent with the guidance provided in GL [Generic Letter] 91-18, the TS LCO for the AFW pump would apply.

Applying the staff position documented in RIS 01-009 to the proposed compensatory measure would require declaring TS equipment in control enclosure room 619 that is relied upon or credited to respond to a main steam or feedwater HELB event in the turbine enclosure when the HELB door is breached inoperable. Also, any TS equipment in the room would be declared inoperable unless the provisions of LCO 3.0.9 can be applied. If LCO 3.0.9 is not applicable, then the appropriate TS conditions of those systems would be entered.

1. Is the TS equipment in control enclosure room 619 considered inoperable under the current TS if the HELB door under consideration is inoperable?

2. Is there any TS equipment in control enclosure room 619 that is relied upon or credited to respond to a main steam or feedwater HELB event in the turbine enclosure?

3. If the answer to either of the previous questions is yes:

a. Which TS LCO action statements is the licensee required to enter if the HELB door under consideration is inoperable?

b. If the license amendment request is approved, does the licensee intend to enter these TS action statements if the HELB door under consideration is maintained open while implementing the supplementary cooling actions? If not, does the LAR request approval for the licensee to not enter these TS action statements if the HELB door under consideration is maintained open while implementing the supplementary cooling actions?

19 In response to audit question 13.a, the licensee stated that NRC approval was requested to breach the HELB door while in the complete loss of main control room cooling 72-hour LCO if a postulated HELB occurred because credited design basis accident mitigation equipment could be rendered inoperable and both units would enter TS 3.0.3 and be placed in at least Operational Condition 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.

As described above, UFSAR Section 15.6.6 describes the plant response to a feedwater line break outside primary containment, which involves a reactor shutdown.

1. Would TS 3.0.3 be entered if the HELB door is breached or only if a HELB occurred while the HELB door is breached?

2. If a HELB event occurs while implementing the supplementary cooling actions, is the licensee assuming that the plant would shut down or continue operations?

3. If the licensee assumes that the plant would shut down if a HELB event occurs while implementing the supplementary cooling actions, how would operators accomplish the plant shutdown? For example:

a. Is any of the equipment that would be relied upon to shut down the plant affected by the HELB in this condition? If so, what alternative equipment would be used to implement the shutdown?

b. Which procedures would operators use to implement the shutdown?

c. Has the licensee verified that these procedures are adequate to shut down the plant if alternative equipment is required?

d. Are any procedure changes required?

e. Is additional training required for operators to be able to shut down the plant if a HELB occurs while implementing the supplementary cooling actions?

ML23313A043 OFFICE NRR/DORL/LPL1/PM NRR/DORL/LPL1/LA NRR/DSS/SCPB/BC NAME AKlett KZeleznock BWittick DATE 11/08/2023 11/13/2023 11/10/2023 OFFICE NRR/DRA/APLC/BC NRR/DSS/STSB/BC NRR/DORL/LPL1/BC NAME SVasavada SMehta HGonzález DATE 11/08/2023 11/09/2023 11/13/2023 OFFICE NRR/DORL/LPL1/PM NAME AKlett DATE 11/13/2023