CNL-24-076, Response to Request for Additional Information Regarding Application to Modify the Technical Specifications for Main Control Room Chiller Completion Time Extension (WBN-TS-23-13)

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Response to Request for Additional Information Regarding Application to Modify the Technical Specifications for Main Control Room Chiller Completion Time Extension (WBN-TS-23-13)
ML25016A068
Person / Time
Site: Watts Bar  
Issue date: 01/16/2025
From: Hulvey K
Tennessee Valley Authority
To:
Office of Nuclear Reactor Regulation, Document Control Desk
References
CNL-24-076
Download: ML25016A068 (1)
v • d • e


Text

1101 Market Street, Chattanooga, Tennessee 37402 CNL-24-076 January 16, 2025 10 CFR 50.90 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Units 1 and 2 Facility Operating Licenses Nos. NPF-90 and NPF-96 NRC Docket Nos. 50-390 and 50-391

Subject:

Response to Request for Additional Information Regarding Application to Modify the Watts Bar Nuclear Plant, Unit 1 and Unit 2 Technical Specifications for Main Control Room Chiller Completion Time Extension (WBN-TS-23-13) (EPID L-2024-LLA-0041)

References:

1. TVA letter to NRC, CNL-24-004, Application to Modify the Watts Bar Nuclear Plant, Unit 1 and Unit 2 Technical Specifications for Main Control Room Chiller Completion Time Extension (WBN-TS-23-13), dated April 4, 2024 (ML24059A159)
2. NRC electronic mail to TVA, Request for Additional Information -TVA LAR to Revise Watts Bar TS 3.7.11 for Main Control Room Chiller Extension of Completion Time (EPID L-2024-LLA-0041), dated November 22, 2024 (ML24327A057)
3.

NRC electronic mail to TVA, RE: RE: Request for Additional Information -TVA LAR to Revise Watts Bar TS 3.7.11 for Main Control Room Chiller Extension of Completion Time (EPID L-2024-LLA-0041),

dated January 2, 2025 (ML25010A075)

In Reference 1, Tennessee Valley Authority (TVA) submitted a request for an amendment to Facility Operating License Nos. NPF-90 and NPF-96 for the Watts Bar Nuclear Plant (WBN), Units 1 and 2, respectively. The proposed change revises WBN Units 1 and 2 Technical Specification (TS) 3.7.11 "Control Room Emergency Air Temperature Control System (CREATCS)," to modify the TS Actions for two inoperable CREATCS trains. The proposed change provides 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> to restore one CREATCS train to operable status provided mitigating actions ensure the control room temperature is controlled. The mitigating actions include the current installation of a non-safety related chiller with a dedicated diesel generator to provide power to the non-safety related system.

In Reference 2, the Nuclear Regulatory Commission (NRC) issued a Request for Additional Information (RAI) and requested that TVA provide a response by January 10, 2025.

U.S. Nuclear Regulatory Commission CNL-24-076 Page 2 January 16, 2025 to this submittal provides a response to the RAI.

In response to NRC RAIs RAI STSB-1 and RAI STSB-2, Enclosure 2 to this submittal provides revised WBN Units 1 and 2 TS Bases pages marked up to show the proposed changes. Changes to the existing TS Bases are provided for information only and will be implemented under the TS Bases Control Program. The TS Bases in Enclosure 2 supersede those provided in Reference 1.

In Reference 3, the NRC granted an extension of this RAI response to January 17, 2025.

This submittal does not change the no significant hazards consideration or the environmental consideration contained in Reference 1. In accordance with Title 10 of the Code of Federal Regulations (10 CFR) 50.91, Notice for public comment; State consultation, a copy of this supplement is being provided to the Tennessee Department of Environment and Conservation.

There are no new regulatory commitments contained in this letter. Please address any questions regarding this request to Amber V. Aboulfaida, Senior Manager, Fleet Licensing, at avaboulfaida@tva.gov.

I declare under penalty of perjury that the foregoing is true and correct. Executed on this 16th day of January 2025.

Respectfully, Kimberly D. Hulvey General Manager, Nuclear Regulatory Affairs & Emergency Preparedness Enclosures

1.

Response to Nuclear Regulatory Commission Request for Additional Information

2.

Revised TS Bases Page Changes (Mark-Ups) for WBN Units 1 and 2 (For Information Only) cc (Enclosure):

NRC Regional Administrator - Region II NRC Senior Resident Inspector - Watts Bar Nuclear Plant NRC Project Manager - Watts Bar Nuclear Plant Director, Division of Radiological Health - Tennessee State Department of Environment and Conservation Digitally signed by Edmondson, Carla Date: 2025.01.16 07:58:33 -05'00' CNL-24-076 E1-1 of 15 Response to Nuclear Regulatory Commission Request for Additional Information NRC Introduction By letter dated April 4, 2024, (Agencywide Documents Access Management System (ADAMS) Accession No. ML24095A159), Tennessee Valley Authority (TVA, the licensee) submitted a license amendment request (LAR) for Watts Bar Nuclear Plant (WBN), Units 1 and 2, to revise Technical Specification (TS) 3.7.11, Control Room Emergency Air Temperature Control System (CREATCS), to: modify the TS Required Actions for two inoperable CREATCS trains; add a new Condition that is applicable in Modes 5 and 6, or during movement of irradiated fuel assemblies; and delete the temporary footnote associated with Condition E.

The purpose of the CREATCS is to provide air temperature control for the main control room (MCR) during normal operation, anticipated transients, and design basis accidents to support operator habitability and operability of the MCR equipment. The CREATCS is not explicitly credited in the accident analysis, but the analyses assume that the MCR temperature supports its purpose. The system has two independent and redundant trains that provide cooling of recirculated air inside the MCR; a single train can provide the required temperature control. WBN, Units 1 and 2, share an MCR.

In the event two CREATCS trains are inoperable, TS 3.7.11, proposed Condition D would be entered, which has a completion time of 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> to restore one CREATCS train to operable status, provided mitigating actions ensure the MCR temperature is controlled. The mitigating actions employ, in part, operator actions. The mitigating actions also include the use of a temporary non-safety related chiller with a dedicated diesel generator to provide power to the non-safety related chiller.

The U.S. Nuclear Regulatory Commission (NRC) staff is currently reviewing the LAR and has identified areas where additional information is needed to complete its review. The requests for additional information (RAIs) are identified below.

Regulatory Basis Appendix A, General Design Criteria for Nuclear Power Plants, to Title 10 of the Code of Federal Regulations (10 CFR), Part 50, Domestic Licensing of Production and Utilization Facilities, establishes the minimum requirements for the principal design criteria for water-cooled nuclear power plants.

WBN, Units 1 and 2, were designed to meet the intent of the Proposed General Design Criteria for Nuclear Power Plant Construction Permits published in July 1967, with the WBN construction permits issued in January 1973. The WBN Dual-Unit Updated Final Safety Analysis Report (UFSAR) (ML23346A225) addresses the General Design Criteria (GDC) specified in Appendix A to 10 CFR Part 50. The specific GDC applicable to this LAR are:

General Design Criterion 4, Environmental and dynamic effects design bases, states that

[s]tructures, systems, and components important to safety shall be designed to accommodate the effects of and to be compatible with the environmental conditions associated with normal operation, maintenance, testing, and postulated accidents, including loss-of-coolant accidents.

CNL-24-076 E1-2 of 15 General Design Criterion 5, Sharing of structures, systems, and components, states that

[s]tructures, systems, and components important to safety shall not be shared among nuclear power units unless it can be shown that such sharing will not significantly impair their ability to perform their safety functions, including, in the event of an accident in one unit, an orderly shutdown and cooldown of the remaining units.

General Design Criterion 19, Control room, states, that [a] control room shall be provided from which actions can be taken to operate the nuclear power unit safely under normal conditions and to maintain it in a safe condition under accident conditions, including loss-of-coolant accidents. Equipment at appropriate locations outside the control room shall be provided: (1) with a design capability for prompt hot shutdown of the reactor, including necessary instrumentation and controls to maintain the unit in a safe condition during hot shutdown, and (2) with a potential capability for subsequent cold shutdown of the reactor through the use of suitable procedures.

General Design Criterion 22, Protection system independence, states, that [t]he protection system shall be designed to assure that the effects of natural phenomena, and of normal operating, maintenance, testing, and postulated accident conditions on redundant channels do not result in loss of the protection function, or shall be demonstrated to be acceptable on some other defined basis.

In 10 CFR 50.36, Technical specifications, the NRC established its regulatory requirements related to the content of TSs. Pursuant to 10 CFR 50.36, TSs are required to include items in the following categories: (1) safety limits, limiting safety system settings, and limiting control settings; (2) limiting conditions for operation (LCOs); (3) surveillance requirements; (4) design features; and (5) administrative controls. The regulation does not specify the requirements to be included in a plants TSs.

The regulation at 10 CFR 50.36(a)(1) states, in part, [a] summary statement of the bases or reasons for such specifications shall also be included in the application, but shall not become part of the technical specifications.

As required in 10 CFR 50.36(c)(2), LCOs are the lowest functional capability or performance level of equipment required for safe operation of the facility. When LCOs are not met, the licensee shall shut down the reactor or follow any remedial action permitted by the TSs until the LCOs can be met.

NUREG-1764, Guidance for the Review of Changes to Human Actions, Revision 1 (ML072640413), provides the NRC staff guidance about the level of review for the human actions (HAs) described in the proposed amendment using a risk-informed approach.

Appendix A to NUREG-1764 contains two tables of generic HAs for boiling-water reactors and pressurized-water reactors (PWRs) that are risk-important. The NRC staff reviewed Table A.2, Generic PWR Human Actions That Are Risk Important, for WBN, Units 1 and 2.

Based on the review of Table A.2, the staff conducted a Level III review, the least stringent, because the operator actions related to the modification of the MCR CREATCS chillers are not considered risk important. For a Level III review, The licensee should provide adequate assurance that the proposed change meets current regulations, except where specific exemptions are requested under 10 CFR 50.12 or 10 CFR 2.802.

CNL-24-076 E1-3 of 15 Requests RAI IOLB-1 TVA previously stated that a qualified person would be in charge and trained on the operation of the temporary chiller (refer to section 3.2.5, Testing and Training, of the LAR dated May 19, 2020 (ML20140A342)). In Section 3.2, MCR Non-Safety Related Chiller Water Equipment Description, of the current LAR, TVA stated, in part, that TVA has decided to retain the non-safety related chiller. However, the LAR does not include information about the qualified individual who will operate the temporary chiller.

a.

Describe any changes to this qualified individuals role and its acceptability now that the temporary non-safety related chiller has been proposed to be retained.

b.

Describe any changes the continued use of the non-safety related chiller may have on the operators workload and how any additional workload will be determined to be acceptable.

TVA Response

a. TVA does not anticipate any change in the qualified individuals role and its acceptability for operation of the non-safety related chiller. Procedural controls will be developed for operation of the non-safety related chiller, which would be a check that the field operator would perform on rounds and poses no additional burden to the operations staff.
b. TVA does not anticipate that the continued use of the non-safety related chiller will have any changes on the operators workload. See the response to part a of this RAI response.

RAI STSB-1 The current TS 3.7.11, condition D states Two CREATCS trains inoperable in MODE 5 or 6, or during movement of irradiated fuel assemblies, with Required Action to suspend movement of irradiated fuel assemblies immediately. Based on LCO 3.7.11 modes of applicability (MODES 1, 2, 3, 4, 5, and 6; during movement of irradiated fuel assemblies),

proposed TS 3.7.11 Condition D allows fuel movement in the modes of applicability for up to 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> before entering Condition F, which requires immediate suspension of movement of irradiated fuel assemblies. Condition F of the proposed change requires entry when Required Action and associated Completion Time of Condition D not met, or during movement of irradiated fuel assemblies.

The proposed bases statement for F.1 conflicts with the proposed TS requirements, as it states:

F.1 In MODE 5 or 6, or during movement of irradiated fuel assemblies, with two CREATCS trains inoperable, action must be taken immediately to suspend activities that could result in a release of radioactivity that might require isolation of the control room. This places the unit in a condition that minimizes risk. This does not preclude the movement of fuel to a safe position.

CNL-24-076 E1-4 of 15 Explain these conflicting statements in the Bases for F.1 allowing fuel moves while in proposed condition D for up to 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> with two CREATCS trains inoperable.

TVA Response TVA has revised the Bases for proposed WBN Units 1 and 2 TS 3.7.11, Condition F.1 for consistency with proposed TS 3.7.11, Condition F.1, which eliminates the conflicting statements noted in the RAI. The revised TS bases are provided in Enclosure 2 to this submittal.

RAI STSB-2 WBN TS section 5.6, Technical Specifications (TS) Bases Control Program, states in part:

5.6.2 Licensees may make changes to Bases without prior NRC approval provided the changes do not require either of the following:

a. A change in the TS incorporated in the license; or
b. A change to the updated FSAR or Bases that requires NRC approval pursuant to 10 CFR 50.59.

The LAR states [c]hanges to the existing TS Bases are provided for information only and will be implemented under the TS Bases Control Program. The Bases markup included in the LAR for Condition A.1 includes the following added text, including the option to provide normal cooling with a non-safety related chiller and the remaining train in standby.

However, there is no corresponding proposed change for TS 3.7.11, Condition A.

a.

Confirm that this proposed Bases change has been evaluated under the TS Bases Control Program. If so, provide responses to requests b and c below.

b.

For the configuration described in the Bases for Condition A.1, state whether the remaining operable train in standby requires any manual action to perform its specified safety function.

c.

As indicated in UFSAR Table 9.4-7 (Sheet 14 of 50), Either Temp. Switch 0-TS-31-88B or Flow Switch 0-FS-31-84 starts redundant Air Handling Unit B-B. If the system is unable to perform automatic initiation of the operable train in standby to meet its specified safety function, provide the basis for the conclusion that the standby train is operable.

TVA Response

a.

TVA has removed the proposed change to WBN Units 1 and 2 TS Bases 3.7.11, Condition A.1; therefore, a response to items b and c of the RAI is not required. The revised TS Bases are provided in Enclosure 2 to this submittal.

CNL-24-076 E1-5 of 15 RAI DORL-1 WBN UFSAR section 9.4.1.3 states, in part, that:

All MCR equipment operates normally at an ambient temperature of 75 °F.

Abnormal excursions of short duration (12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> or less) to 104 °F maximum and 60 °F minimum may occur without adverse effects on the equipment.

These sorts of temperature limits (on equipment or the location where the equipment is located) are typically established based on equipment design specifications and equipment environmental qualification reports.

The current LAR states, As noted in References 1 and 3, the 90 °F temperature limit provides adequate margin between the normal MCR operating temperature of 75 °F and a limit that ensures that the equipment operability limit of 104 °F is not exceeded. The May 19, 2020, LAR (i.e., Reference 1), stated that the provision (i.e., the MCR temperature exceeds 90 °F or the duration without a train of CREATCS being operable exceeds four days) is only applicable during pre-planned modification and testing activities for the upgrade of the MCR chillers.

In TS 3.7.11, Condition D, TVA proposes to allow the temperature in the MCR to go up to 90 °F for up to 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> to allow the restoration of one train of CREATCS to operable on a permanent basis. However, TVA has not provided any information regarding why or how the 90 °F temperature limit ensures equipment operability.

Justify the proposed 90 °F temperature limit (for up to 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br />) in the proposed Action D.2 and explain how this limit ensures equipment operability in the event of the loss of cooling function.

TVA Response The proposed 90°F temperature limit in the proposed changes to TS 3.7.11, Condition D was selected to provide an adequate margin between the normal ambient temperature limit (75°F) and the abnormal temperature limit (104°F) for the MCR. The normal MCR temperature limit is also documented in the WBN Technical Requirements Manual (TRM)

Table 3.7.5-1 and is based on a TVA dual-unit operational analysis for the WBN MCR using conservative electrical heat loads. The abnormal temperature limit for the MCR is documented in TVA calculation MDQ00003120090157, Revision 7, which was reviewed by the NRC in Reference 1 of this RAI response.

As previously noted in Reference 2 of this RAI response, If the temporary chiller system were to fail, the MCR could heat up as described in Calculation MDQ00003120090157, Revision 7, which indicates that the MCR heat-up from 75°F to 104°F would take about 5.28 hours3.240741e-4 days <br />0.00778 hours <br />4.62963e-5 weeks <br />1.0654e-5 months <br />. Because operators will be monitoring the MCR temperature every hour, it could take the MCR operators an hour to discover that the MCR temperature had risen beyond 90°F, which would leave approximately 4.28 hours3.240741e-4 days <br />0.00778 hours <br />4.62963e-5 weeks <br />1.0654e-5 months <br /> of continued heat up before the MCR temperature reaches 104°F. Additionally, the WBN dual-unit Updated Final Safety Analysis Report (UFSAR) Section 9.4.1.3 states, All MCR equipment operates normally at an ambient temperature of 75°F. Abnormal excursions of short duration (12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> or CNL-24-076 E1-6 of 15 less) to 104°F maximum and 60°F minimum may occur without adverse effects on the equipment.

By maintaining the MCR temperature at or below 90°F, the operability requirements for safety-related functions provided by equipment and instrumentation in the MCR, as well as habitability needs for operating personnel, are satisfied. The temperature limit for control room equipment operability is 104°F. Utilizing a 90°F limit and monitoring this value hourly ensures that the 104°F limit is not exceeded. The non-safety related chiller system has cooling capacity that meets or exceeds the safety related chiller capacity and could maintain MCR temperature at the normal operating temperature limit for worst-case normal heat load conditions or at loss of coolant accident (LOCA) temperature limits during a LOCA event.

Additionally, in Reference 3 of this RAI response, the NRC evaluated the acceptability of the 90°F temperature limit during the proposed MCR chiller replacement project and determined it to be acceptable. The basis for the 90°F temperature limit remains applicable for this license amendment request. Furthermore, in Reference 4 of this RAI response, NRC approved a similar temperature limit for the Sequoyah Nuclear Plant (SQN), Units 1 and 2 for their one-time change during maintenance activities to upgrade their Control Room Air-Conditioning System compressors.

Additionally, the NRC requested how the 90°F temperature limit ensures equipment operability in the event of the loss of cooling function. Thermal life of various electrical and mechanical equipment is one of several important aging concerns in the qualification of hardware. The requirement is that the equipment remains functional during and after specified design basis events. In addition to the above 90°F temperature limit, WBN Units 1 and 2 TRM Technical Requirement 3.7.5, Area Temperature Monitoring, Required Action A.1 requires whenever the temperature in one or more areas have exceeded the normal temperature limits (including the MCR) for greater than eight hours, document the exceedance in accordance with the Corrective Action Program and include an analysis to demonstrate the operability of the affected equipment. The report must contain the cumulative time and the amount by which the temperature has exceeded the limits.

Only when the temperature has exceeded the abnormal limit (104F) is action required to be taken. TRM 3.7.5 Action B.1.1 requires the area temperature to be restored below the normal temperature limit (80F) within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. If the temperature is not restored, Action B.1.2 requires the affected equipment to be declared inoperable within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> and completion of action B.2 to document the condition in the TVA corrective action program (CAP) and an analysis of Operability be performed for the affected equipment based on time and magnitude of the exceedance. As can be seen from the TR 3.7.5 bases, the concern that drives the monitoring of temperature in the MCR is one of thermal life.

The TRM is not indicating that the equipment will fail if the temperature exceeds 80F. To the contrary, a scenario where the temperature exceeds 80F (but remains less than the 104F abnormal limit) for less than 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> requires no action. Temperatures between 80F and 104F that last greater than 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> are required to be documented in the CAP and analyzed for impact to the thermal life of affected equipment. In the event that cooling has not been restored through either the safety related chillers or a temporary chiller, the MCR temperature will exceed the 104F limit requiring entry into TRM 3.7.5 Condition B regardless of this LAR. Additionally, the proposed change to WBN Units 1 and 2 TS 3.7.11 requires entry into Mode 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-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 /> if both CREATCS trains are inoperable and the MCR temperature exceeds 90F.

CNL-24-076 E1-7 of 15 Therefore, maintaining control room temperatures at or below 90°F will ensure that the safety-related functions are operable and provide sufficient time before reaching equipment operability limits to take necessary plant actions.

References for TVA Response to RAI DORL-1

1. NRC letter to TVA, Watts Bar Nuclear Plant, Units 1 and 2 - Regulatory Audit Summary Related to Request to Technical Specification 3.7.11, Control Room Emergency Air Temperature Control System (CREATCS) (EPID L-2020-LLA-0114), dated January 26, 2021 (ML21012A084)
2. TVA letter to NRC, CNL-20-091, Response to Request for Additional Information Regarding Application to Modify the Watts Bar Nuclear Plant Unit 1 and Unit 2 Technical Specifications for Main Control Room Chiller Completion Time Extension (WBN-TS-18-16) (EPID L-2020-LLA-0114), dated December 16, 2020 (ML20351A424)
3. NRC letter to TVA, Watts Bar Nuclear Plant, Units 1 and 2 - Issuance of Amendment Nos. 145 and 51 for One-Time Change to Technical Specification 3.7.11 to Extend the Completion Time for Main Control Room Chiller Modifications (EPID L-2020-LLA-0114),

dated May 5, 2021 (ML21078A484)

4. NRC letter to TVA, Sequoyah Nuclear Plant, Units 1 and 2, Issuance of Amendments Regarding One-Time Temporary Revision of Control Room Air-Conditioning System, dated May 21, 2004 (ML041460534).

RAI SCPB-1 In the LAR, TVA provides operating experience to justify the proposed 96-hour completion time for restoring one train of CREATCS when two trains are inoperable (i.e., proposed Condition D). The NRC staff notes that the times for restoring one train of CREATCS to operable status cited in the LAR were for entry into Condition A, which allows a flexible restoration period to restore one train of CREATCS to operable within the 30-day Completion Time. The NRC staff also notes that the times given in the LAR for the recent MCR chiller outages are for the total outage time, not necessarily the time to restore the train to operable. The times cited in Table 3 of Reference 1 (ML20140A342) in the LAR are also the amount of time the chiller was unavailable, not the amount of time to restore the train to operable.

TVA cites the Braidwood amendments issued in 2018, and the Catawba amendments issued in 2024 as precedence. In those LARs, the licensees cite operating experience related to two trains inoperable, which requires a more expedited restoration and is more appropriate for TVAs proposed Condition D. In those instances, one train of CREATCS was restored to operable within 23 hours2.662037e-4 days <br />0.00639 hours <br />3.80291e-5 weeks <br />8.7515e-6 months <br /> or less. In the NRC staffs safety evaluations, the staff found that the proposed 24-hour Completion Time was consistent with precedent and industry experience that has shown a 24-hour Completion Time provides a reasonable time to restore operability to at least one train of CREATCS. Therefore, the staff does not see any relevance of the referenced precedence regarding industry experience to justify the extended 96-hour completion time.

TVA provided list of events in the LAR resulting in both WBN CREATCS trains inoperable and, based on the licensee event reports, were resolved well under the 24-hour duration.

CNL-24-076 E1-8 of 15 May 9, 1997, TVA reported an event for WBN, Unit 1 (ML073250262). - Condition was resolved in 3 minutes September 24, 1998, TVA reported an event for WBN, Unit 1 (ML073250317) -

Condition was resolved in 6 minutes August 7, 2019, TVA reported an event for WBN, Unit 1 (ML19219A219) - Event was not directly related to CREATCS failure and condition was resolved in 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> As indicated in LAR:

There are TS in the Westinghouse improved STS (NUREG-1431, Revision 5) which provide a Completion Time for two inoperable filtration systems due to an inoperable building boundary. These include TS 3.7.10, Control Room Emergency Filtration System, TS 3.7.12, Emergency Core Cooling System Pump Room Exhaust Air Cleanup System, and TS 3.7.13, Fuel Building Air Cleanup System. The Completion Time was found to be acceptable for these TS based on the low probability of an event and the use of compensatory measures.

These are based on a 24-hour Completion Time which was found to be acceptable based on the low probability of an event and the use of compensatory measures.

The NRC staff notes that the initial basis for the 96-hour delayed entry into LCO 3.0.3 cited in the LAR, dated May 19, 2020, was approved on a one-time basis to allow post-maintenance testing (PMT) following the replacement of the MCR chiller(s). TVA noted that during testing of the modified train, there may be cooling water flow and/or air flow anomalies, therefore, a delayed entry into LCO 3.0.3 was needed to allow stabilization of the water and air flow from the modified CREATCS train during PMT. The NRC staff cited this basis in its safety evaluation dated May 5, 2021 (ML21078A484). In the current LAR, TVA is requesting a delayed entry into proposed Condition E no matter the cause of the two trains being inoperable.

Provide a justification and basis for the proposed 96-hour Completion Time to restore one train of CREATCS to operable in proposed Condition D.

TVA Response As noted in the RAI, the original basis for the 96-hour Completion Time to restore one CREATCS to operable status in the proposed Condition D of WBN Units 1 and 2 TS 3.7.11 in Reference 1 of this RAI response was evaluated by the NRC in Reference 2 of this RAI response, which stated: The LAR proposed a one-time change to the footnote for the TS 3.7.11, Condition E, completion time to allow a 4-day delayed entry into LCO 3.0.3.

The licensee stated that 4 days is a reasonable timeframe to perform maintenance to restore an inoperable CREATCS train to an operable status based on a review of Maintenance Rule unplanned unavailability data for the CREATCS chillers from March 2015 to March 2020. As noted in Section 3.4.2 of Reference 3 of this RAI response, TVA provided a table providing the maintenance history of the CREATCS and stated that four days is expected to be sufficient time to restore at least one CREATCS train to operable status while minimizing the length of time in which the CREATCS is inoperable and potentially avoiding unnecessary impact to plant operations. It should also be noted that there is also regulatory precedence for an even greater than 96-hour delayed entry into TS 3.0.3 if both control room air temperature control train are out of service. For CNL-24-076 E1-9 of 15 example, a license amendment was issued by the NRC for SQN for the control room air-conditioning system (CRACS), which allowed both trains of the CRACS to be inoperable for up to 7 days, provided control room temperatures were verified every four hours to be less than or equal to 90°F (Reference 4 of this RAI response). While these license amendments were on a one-time basis to support replacement of the MCR chillers, the rationale for the extended completion time prior to entering LCO 3.0.3 still applies to this LAR. As requested by the NRC, the following provides additional information to support the 96-hour Completion Time to restore one train of CREATCS to operable in proposed Condition D.

The RAI states The NRC staff notes that the times for restoring one train of CREATCS to operable status cited in the LAR were for entry into Condition A, which allows a flexible restoration period to restore one train of CREATCS to operable within the 30-day Completion Time. However, it should be noted that when a CREATCS train becomes inoperable, although WBN Units 1 and 2 TS 3.7.11 currently allows a 30-day Completion Time to restore the inoperable CREATCS train to operable status, TVA works expeditiously, in a safe manner to restore the operability of the affected CREATCS train, in order to avoid the potential for entry into LCO 3.0.3 if the other CREATCS train becomes inoperable.

Monitoring, trending, and reporting data was used as a basis to qualify the requested 96-hour completion time for the WBN CREATCS function. The CREATCS are risk significant contributors by program definition. Emphasis was placed on unplanned unavailability events that included functional failures that required a Cause Determination and Evaluation (CDE) for each event. The unplanned hours of availability were best suited for the review considering there was no pre-planning for the event opposed to planned unavailability.

The unplanned hours listed in each event were verified to agree with actual LCO entry and exit times when available, utilizing operations narrative logs and ensuring that the necessary clearance activities, maintenance, and testing were included. Work documents and clearance records were also reviewed when available to ensure the corrective actions were performed with minimal unnecessary delays. The unavailable hours were averaged for thirty events with durations greater than a single shift, considering that the single shift events mostly consisted of reset and restarts with a short period of monitoring.

Further justification for the proposed 96-hour Completion Time occurred during two recent events where WBN had to enter LCO 3.0.3 as a result of the inoperability of both CREATCS trains. The first event occurred in November 2024, during the CREATCS-A component outage when MCR-B Chiller tripped. The second event occurred in January 2025 during a CREATCS-B component outage when MCR-A Chiller tripped. The team was able to complete the planned and unplanned work to restore both trains promptly. A timeline of TS entry and exit times is included in Table RAI SCPB-1-1.

Results of unplanned hour averaging was determined to be 90.6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> from discovery of event to declaration of operability. Specific values are included in Table RAI SCPB-1-2.

The work management team will prioritize on repairing the CREATCS train that has the potential to be returned to service in the 96 hour0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> completion time. The average completion times could be challenging while performing future chiller replacements if, with one train of CREATCS is out of service for an extended period of time, the opposite train chiller in standby was discovered to be inoperable.

CNL-24-076 E1-10 of 15 Table RAI SCPB-1 TS LCO Entry and Exit Times Ops Log Date/Time TS Status 11/19/2024 13:20 B11 Entry 11/22/2024 18:18 A11 Entry 11/22/2024 19:37 B11 303 Entry 11/23/2024 1:45 B11 303 Exit 11/25/2024 3:30 A11 Entry 11/25/2024 4:03 A11 Exit 11/25/2024 15:12 B11 Entry 11/25/2024 22:32 B11 Exit 12/27/2024 11:30 B11 Entry 1/4/2025 8:55 A11 303 Entry 1/4/2025 15:14 A11 303 Exit 1/6/2025 20:00 B11 Exit Legend B11 = Train B LCO 3.7.11, A11 = Train A LCO 3.7.11, 303 = LCO 3.0.3 Table RAI SCPB-1 Average Unplanned Hours by Event Train Maximum Unplanned Hours Minimum Unplanned Hours Count of Events Avg Unplanned Hours A

173.7 37.5 18 80.8 B

241.1 41.6 12 105.3 Avg 90.6 = [(80.8 x 18) +(105.3 x 12)]/30 CNL-24-076 E1-11 of 15 Because Table RAI SCPB-1-2 provides an average outage duration of greater than 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> for restoration of an unplanned inoperable CREATCS train to service, a proposed 96-hour Completion Time is reasonable to allow for any additional unforeseen circumstances that may occur during the repair of an inoperable CREATCS train. The proposed 96 hour0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> Completion Time will only apply when both CREATCS trains are out of service. In that case site personnel would work expeditiously to restore a CREATCS train to service in order to avoid entering TS LCO 3.0.3.

Based on the information in this RAI response, the proposed 96 hour0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> extension of TS 3.7.11 Condition D provides a reasonable time to address operating problems with the CREATCS and, as described in Reference 1 of this RAI response, is considered acceptable given the mitigating actions described in the proposed Bases for Conditions D.1, D.2, and D.3, and the low probability of an accident that would require the CREATCS. Furthermore, the proposed 96 hour0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> Completion Time provides a reasonable time to diagnose, plan, repair, and test most problems with the CREATCS, while minimizing the period of time that control room occupants might have to respond to an event while utilizing the mitigating actions.

Therefore, 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> is sufficient time in most circumstances to restore at least one CREATCS train to operable status while minimizing the length of time in which the CREATCS is inoperable and potentially avoiding unnecessary impact to plant operations.

References for TVA Response to RAI SCPB-1

1. TVA letter to NRC, CNL-24-004, Application to Modify the Watts Bar Nuclear Plant, Unit 1 and Unit 2 Technical Specifications for Main Control Room Chiller Completion Time Extension (WBN-TS-23-13), dated April 4, 2024 (ML24059A159)
2. NRC letter to TVA, Watts Bar Nuclear Plant, Units 1 and 2 - Issuance of Amendment Nos. 145 and 51 for One-Time Change to Technical Specification 3.7.11 to Extend the Completion Time for Main Control Room Chiller Modifications (EPID L-2020-LLA-0114),

dated May 5, 2021 (ML21078A484)

3. TVA letter to NRC, CNL-20-012, Application to Modify the Watts Bar Nuclear Plant, Unit 1 and Unit 2 Technical Specifications for Main Control Room Chiller Completion Time Extension (WBN-TS-18-16), dated May 19, 2020 (ML20140A342)
4. NRC letter to TVA, Sequoyah Nuclear Plant, Units 1 and 2, Issuance of Amendments Regarding One-Time Temporary Revision of Control Room Air-Conditioning System, dated May 21, 2004 (ML041460534).

RAI SCPB-2 The May 19, 2020, LAR indicated that the non-safety related chiller in conjunction with the existing CREATCS air handling units would be capable of providing adequate cooling to maintain the MCR conservatively below 80 °F. In its letter, dated May 5, 2021, the NRC approved this LAR as a one-time amendment that allowed the use of a temporary, non-safety related chiller to support MCR cooling during the replacement of the CREATCS chillers.

The current LAR describes plans to use a non-safety related chiller to provide backup cooling in the event both CREATCS trains become inoperable. Section 3.2 of the current LAR provides a description of the non-safety related chiller and refers to the May 19, 2020, LAR, the December 16, 2020, RAI response (ML20351A424), the May 5, 2021, safety evaluation, and the NRC regulatory audit summary (ML21012A084).

CNL-24-076 E1-12 of 15

a. Describe any differences between the temporary non-safety related chiller system from the previously reviewed configuration, and the proposed non-safety related chiller equipment and configuration to support the mitigating measures proposed in the current LAR.
b. Confirm that the sizing of the non-safety related chiller and related heatup calculation referenced in the May 19, 2020, LAR are bounding for the proposed non-safety related chiller configuration referred to in the current LAR.
c. The NRC staff notes that in TVA letter CNL-23-015, dated February 27, 2023 (ML23058A447), TVA identified several changes from the May 19, 2020, LAR (Table 2) and the NRC regulatory audit summary (Table 3), and what TVA has currently planned (as of February 27, 2023). One such change is going from a 2.5-inch diameter supply and return hose to 3-, 4-, and 6-inch hoses. However, TVA did not include any information on potential flooding impacts and line breaks due to the larger size hoses. Describe any potential impacts due to the change in hose sizes. Additionally, describe any changes to the control room envelope penetrations, piping connections, and locations due to the larger hose sizes or other reasons that differ from what have been previously described and included on the docket.

TVA Response

a. Differences between the currently planned MCR temporary chiller equipment and the MCR temporary chiller equipment, as described in Section 3.1 to Reference 1 of this RAI response and the NRC Regulatory Audit Summary (Reference 2 of this RAI response), were provided to the NRC in Tables 1 and 2 of Reference 3 of this RAI response. There is an additional difference that will be included in the temporary non-safety chiller system to support the current LAR (Reference 4 of this RAI response).

The additional difference is an improvement in the design of the temporary non-safety related chiller system to provide installation efficiency and operational flexibility regarding permanent penetrations and is described in Table RAI SCPB-2-1 of this RAI response. As noted in this table, the permanent penetrations result in a more robust installation compared to the previously planned temporary configuration.

CNL-24-076 E1-13 of 15 Table RAI SCPB-2-1 Previously Reviewed Configuration Currently Planned Installation Reason for Change Significance Two temporary penetrations (2-1/2) were to be used in the floor of the west mechanical equipment room at the Control Room Envelope (CRE) boundary for chilled water to/from the MCR Air Handling Units (AHUs). The design of the temporary piping and ball valve at each penetration was to utilize threaded fittings.

The valves, attached piping, baseplate, and anchorage were to be classified as Seismic Category I(L)A position retention and pressure boundary.

Permanent penetrations (2-1/2) are being installed via a permanent plant modification and will be used at the CRE boundary.

The penetrations will use welded fittings, piping and ball valves which will be qualified to Seismic Category I per TVA Seismic Design Criteria. The two permanent penetrations will utilize 2-1/2 piping at the penetrations, consistent with the previously planned temporary penetration piping.

The two sections of penetration piping will each include a loop seal.

Installation of permanent penetrations will reduce the time to install the temporary chiller system and associated hoses compared to needing to install and remove temporary penetrations and associated piping and hardware each time the temporary chiller is installed. The inclusion of loop seals in the design will eliminate the need for a breach permit when the penetrations are in use.

The permanent penetrations result in a more robust installation compared to the previously planned temporary configuration. A breach permit will not be required.

b. The temporary non-safety related chiller will be sized for greater than 150 tons, which is consistent with the sizing requirements described in Reference 1 of this RAI response and verified during the associated NRC audit (Reference 2 of this RAI response) and the NRC Safety Evaluation (Refence 5 of this RAI response). The heatup calculation described in Reference 1 of this RAI response remains bounding. Because the heatup calculation is bounding, the various structures, systems, and components (SSC) that are provided cooling retain their ability to perform their intended design functions.

Therefore, TVA confirms that the sizing of the non-safety related chiller and related heatup calculation referenced in the May 19, 2020, LAR (Reference 1 of this RAI response) are bounding for the proposed non-safety related chiller configuration referred to in the current LAR (Reference 4 of this RAI response).

c. The larger hoses described in Reference 3 of this RAI response will be primarily located in the plant yard near the temporary chiller. Hoses in the mechanical equipment room CNL-24-076 E1-14 of 15 between the floor penetrations and the branch connections at the AHUs will be three inches. The two hoses in the mechanical equipment room (supply and return to the AHUs) are approximately 20 feet in length each.

The permanent penetrations through the floor of the mechanical equipment room at the CRE consist of two 2.5 inch pipes, consistent with Reference 1 of this RAI response.

The pipes will increase to three inches after penetrating the floor (top and bottom side) and connect to three-inch hoses to/from the AHUs (in the mechanical equipment room) and to/from the temporary chiller (in the plant yard). The three-inch pipes on the mechanical equipment room side of the penetrations will contain loop seals to preclude the need for a breach permit when a temporary chiller system is in operation.

The 2.5 inch penetration and attached three-inch piping including loop seals and ball valves will be seismically qualified. The ball valves will be closed when the temporary cooling system is not in service, and the hoses are disconnected. Both the loop seals and the closed ball valve will protect the CRE envelope such that a breach permit is not required for the penetration, once installed via a permanent plant modification.

The larger hose sizes result in an increase in the temporary system volume. The volume of the temporary system with the larger hoses sizes remains less than the volume of the MCR B chilled water system, which is the bounding case used in the moderate energy line break (MELB) fooding calculation. Because the MELB flooding calculation remains bounding, the amount of internal flooding due to a MELB event will not exceed the calculation internal flooding height and there will be no new adverse impact to any associated SSC design function as a result.

References for TVA Response to RAI SCPB-2:

1. TVA letter to NRC, CNL-20-012, Application to Modify the Watts Bar Nuclear Plant Unit 1 and Unit 2 Technical Specifications for Main Control Room Chiller Completion Time Extension (WBN-TS-18-16), dated May 19, 2020 (ML20140A342)
2. NRC letter to TVA, Watts Bar Nuclear Plant, Units 1 and 2 - Regulatory Audit Summary Related to Request to Technical Specification 3.7.11, Control Room Emergency Air Temperature Control System (CREATCS) (EPID L-2020-LLA-0114), dated January 26, 2021 (ML21012A084)
3. TVA letter to NRC, CNL-23-015, Expedited Application to Modify the Watts Bar Nuclear Plant, Unit 1 and Unit 2 Technical Specifications for Main Control Room Chiller Completion Time Extension (WBN-TS-22-08), dated February 27, 2023 (ML23058A447)
4. TVA letter to NRC, CNL-24-004, Application to Modify the Watts Bar Nuclear Plant, Unit 1 and Unit 2 Technical Specifications for Main Control Room Chiller Completion Time Extension (WBN-TS-23-13), dated April 4, 2024 (ML24059A159)
5. NRC letter to TVA, Watts Bar Nuclear Plant, Units 1 and 2 - Issuance of Amendment Nos. 145 And 51 for One-Time Change to Technical Specification 3.7.11 to Extend the Completion Time for Main Control Room Chiller Modifications (EPID L-2020-LLA-0114),

dated May 5, 2021 (ML21078A484)

CNL-24-076 E1-15 of 15 RAI EMIB-1 Section 9.4.1.3, Safety Evaluation, of the WBN UFSAR states that the control building air-conditioning systems are engineered safety feature (ESF) equipment. Section 3.2, MCR Non-Safety Related Chilled Water Equipment Description, of the LAR states that the non-safety related chiller was initially planned to be a temporary system during the MCR CREATCS chiller project, but that TVA has decided to retain the non-safety related chiller.

Therefore, TVA proposes to have the chiller and supporting equipment available to be attached to the existing air handling units through permanent connections in the CREATCS chilled water loop. Further, the proposed change to the TS Bases on page B 3.7-60 indicates that the proposed chiller modification includes the option to provide normal cooling with a non-safety related chiller and the remaining train in standby. Additionally, the proposed Bases for Conditions D.1, D.2, and D.3 state that a non-safety related chiller system with a diesel generator to provide power to the non-safety related system will be operated.

a.

With the assumed use of the proposed non-safety related chiller system to perform an ESF function, discuss the applicability of the chiller system, including its pumps, valves, and dynamic restraints, to the requirements in paragraph ISTA-1100, Scope, of Subsection ISTA, General Requirements, in the American Society of Mechanical Engineers (ASME) Code for Operation and Maintenance of Nuclear Power Plants (OM Code), 2004 Edition through the 2006 Addenda (current OM Code of Record for WBN, Units 1 and 2) as incorporated by reference in 10 CFR 50.55a, Codes and standards.

b.

If the non-safety related chiller system is justified to be outside the scope of ISTA-1100, describe the periodic testing and maintenance activities that will demonstrate the operational readiness of the non-safety related components within the chiller system to perform the ESF functions of the CREATCS.

c.

In 10 CFR 50.65(b), the NRC states that the scope of the monitoring program specified in 10 CFR 50.65(a)(1) is to include non-safety related structures, systems, and components whose failure could cause a reactor scram or actuation of a safety-related system. Based on the proposed TS Bases statement for Conditions D.1, D,2, and D.3 regarding use of the non-safety chiller and standby safety-related chiller configuration, confirm that the non-safety related chiller system will be incorporated into the Maintenance Rule program.

TVA Response

a. The non-safety related chiller system including its pumps, valves, and dynamic restraints, are not subject to the requirements of paragraph ISTA-1100 in the ASME OM Code, 2004 Edition through the 2006 Addenda.
b. The periodic testing and maintenance activities of the non-safety related chiller system is performed in accordance with the vendor recommendations.
c. The non-safety related chiller system does not satisfy the requirements for inclusion in the Maintenance Rule program because its failure would not cause a reactor scram or actuation of a safety-related system.

CNL-24-076 Revised TS Bases Page Changes (Mark-Ups) for WBN Units 1 and 2 (For Information Only)

CREATCS B 3.7.11 BASES Watts Bar-Unit 1 B 3.7-54 Revision 64, 162, 172, Amendment 50, 132, 145, ACTIONS C.1 and C.2 (continued)

(continued)

An alternative to Required Action C.1 is to immediately suspend activities that present a potential for releasing radioactivity that might require isolation of the control room. This places the unit in a condition that minimizes accident risk.

This does not preclude the movement of fuel to a safe position.

D.1, D.2, and D.3 If both CREATCS trains are inoperable, the CREATCS may not be capable of performing its intended function. Therefore, the control room area temperature is required to be monitored to ensure that temperature is being maintained low enough that equipment in the control room is not adversely affected and habitability is maintained. The following mitigating actions will be used to maintain control room area temperature A non-safety related chiller system with a DG to provide power to the non-safety related system will be operated.

With both CREATCS trains inoperable, TVA will employ a graded approach to defense-in-depth and protected equipment strategies based on the operating status of the affected unit. The risk of the activity will be assessed and managed, including the use of physical barriers as needed.

TVA procedures will preclude work on or near protected equipment and limit access to the area to emergency situations and non-intrusive monitoring of running equipment per operator rounds.

Other mitigating actions such as opening cabinet doors, use of fans to circulate air within the MCRHZ, use of ice vests, may be employed.

With the control room temperature being maintained within the temperature limit, 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> is allowed to restore a CREATCS train to OPERABLE status. This Completion Time is reasonable considering that the main control room (MCR) temperature is being maintained within limits and the low probability of an event occurring requiring control room isolation (Ref 4). The specified temperature limit of 90°F is above the normal operating temperature of the MCR (approximately 75°F), providing operational flexibility when implementing the mitigating actions.

This temperature does not impact the operability of equipment or habitability of the MCR. The limit of 90°F maintains margin below the lowest specification for the MCR equipment cabinets of 104°F (Ref. 4).In MODE 5 or 6, or during movement of irradiated fuel assemblies, with two CREATCS trains inoperable, action must be taken immediately to suspend activities that could result in a release of radioactivity that might require isolation of the control room. This places the unit in a condition that minimizes risk. This does not preclude the

CREATCS B 3.7.11 BASES Watts Bar-Unit 1 B 3.7-54a Revision 64, 162, 172, Amendment 50, 132, 145, ACTIONS movement of fuel to a safe position.

(continued)

E.1 and E.2 In MODE 1, 2, 3, or 4, if the inoperable CREATCS trains cannot be restored to OPERABLE status within the required Completion Time, the unit must be placed in a MODE that minimizes the risk. 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 unit systems.

If both CREATCS trains are inoperable in MODE 1, 2, 3, or 4 the CREATCS may not be capable of performing its intended function. Therefore, LCO 3.0.3 must be entered immediately. The Completion Time is modified by a footnote that states an allowance to monitor the main control room temperature every hour and verify the main control room temperature is less than or equal to 90°F is permitted for up to four days in lieu of the immediate entry into LCO 3.0.3. If the main control room temperature exceeds 90°F, or the duration without a train of CREATCS being OPERABLE exceeds four days, immediate entry into LCO 3.0.3 is required. This provision is only applicable during modification activities planned for the upgrade of the main control room chillers beginning no earlier than July 1, 2023, and ending no later than December 31, 2024, provided the following compensatory measures are implemented as described in TVA letter CNL-20-012, dated May 19, 2020.

  • A temporary, non-safety related chiller system with a temporary DG to provide power to the temporary chiller system will be installed and operated as described in the LAR.
  • Instructions for operation of the temporary cooling equipment will be provided.
  • During replacement of the CREATCS chillers, TVA will employ a graded approach to defense-in-depth and protected equipment strategies based on the operating status of the affected unit. The risk of the activity will be assessed and managed, including the use of physical barriers as needed. Additionally, TVA procedures preclude work on or near protected equipment and limit access to the area to emergency situations and non-intrusive monitoring of running equipment per operator rounds.
  • During replacement of the CREATCS chillers, no elective maintenance will be performed on TS related support equipment for the Operable CREATCS chiller except for any required TS SRs.

The purpose of the footnote is to ensure the MCR temperature is being controlled. The specified temperature limit of 90°F is above the normal operating temperature of the MCR (approximately 75°F), providing operational flexibility when implementing the mitigating actions. This temperature does not impact the operability of equipment or habitability of the MCR. The limit of 90°F maintains margin below the lowest specification for the MCR equipment cabinets of 104°F.

CREATCS B 3.7.11 BASES Watts Bar-Unit 1 B 3.7-54a Revision 64, 162, 172, Amendment 50, 132, 145, Subsequent to immediate MCR temperature verification, the one-hour frequency is adequate given the indications available in the MCR. Main control room temperature data is measured and displayed from readily available equipment in the MCR and operators will have awareness of temperature trending relative to the 90°F limit.

F.1 If the Required Action and associated Completion Time of Condition D is not met in MODE 5 or 6, or during movement of irradiated fuel assemblies, with two CREATCS trains inoperable, action must be taken immediately to suspend activities that could result in a release of radioactivity that might require isolation of the control room. This places the unit in a condition that minimizes risk. This does not preclude the movement of fuel to a safe position.

SURVEILLANCE SR 3.7.11.1 REQUIREMENTS This SR verifies that the heat removal capability of the system is sufficient to remove the heat load assumed in the sizing calculations in the control room.

This SR consists of a combination of testing and calculations. This is accomplished by verifying that the system has not degraded. The only measurable parameters that could degrade undetected during normal operation are the system air flow and chilled water flow rate. Verification of these two flow rates will provide assurance that the heat removal capacity of the system is still adequate. The Surveillance Frequency is controlled under the Surveillance Frequency Control Program.

REFERENCES

1.

Watts Bar FSAR, Section 9.4.1, "Control Room Area Ventilation System."

2.

Watts Bar FSAR, Section 3.7.3.18, Seismic Qualification of Main Control Room Suspended Ceiling and Air Delivery Components.

3.

NRC Safety Evaluation dated February 12, 2004, for License Amendment 50.

4.

NRC Safety Evaluation dated May 5, 2021, for License Amendment 145

CREATCS B 3.7.11 Bases (continued)

Watts Bar - Unit 2 B 3.7-62 Revision 47, 71, Amendment 51, 69, ACTIONS (continued)

C.1 and C.2 (continued)

In MODE 5 or 6, or during movement of irradiated fuel, if the inoperable CREATCS train cannot be restored to OPERABLE status within the required Completion Time, the OPERABLE CREATCS train must be placed in operation immediately. This action ensures that the remaining train is OPERABLE, that no failures preventing automatic actuation will occur, and that active failures will be readily detected.

An alternative to Required Action C.1 is to immediately suspend activities that present a potential for releasing radioactivity that might require isolation of the control room. This places the unit in a condition that minimizes accident risk. This does not preclude the movement of fuel to a safe position.

D.1, D.2, and D.3 If both CREATCS trains are inoperable, the CREATCS may not be capable of performing its intended function. Therefore, the control room area temperature is required to be monitored to ensure that temperature is being maintained low enough that equipment in the control room is not adversely affected and habitability is maintained. The following mitigating actions will be used to maintain control room area temperature A non-safety related chiller system with a DG to provide power to the non-safety related system will be operated.

With both CREATCS trains inoperable, TVA will employ a graded approach to defense-in-depth and protected equipment strategies based on the operating status of the affected unit. The risk of the activity will be assessed and managed, including the use of physical barriers as needed.

TVA procedures will preclude work on or near protected equipment and limit access to the area to emergency situations and non-intrusive monitoring of running equipment per operator rounds.

Other mitigating actions such as opening cabinet doors, use of fans to circulate air within the MCRHZ, use of ice vests, may be employed.

With the control room temperature being maintained within the temperature limit, 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> is allowed to restore a CREATCS train to OPERABLE status. This Completion Time is reasonable considering that the main control room (MCR) temperature is being maintained within limits and the low probability of an event occurring requiring control room

CREATCS B 3.7.11 Bases Watts Bar - Unit 2 B 3.7-62a Revision 47, Amendment 51, ACTIONS (continued)

D.1, D.2, and D.3 (continued) isolation (Ref 4). The specified temperature limit of 90°F is above the normal operating temperature of the MCR (approximately 75°F), providing operational flexibility when implementing the mitigating actions. This temperature does not impact the operability of equipment or habitability of the MCR. The limit of 90°F maintains margin below the lowest specification for the MCR equipment cabinets of 104°F (Ref. 4).In MODE 5 or 6, or during movement of irradiated fuel assemblies, with two CREATCS trains inoperable, action must be taken immediately to suspend activities that could result in a release of radioactivity that might require isolation of the control room. This places the unit in a condition that minimizes risk. This does not preclude the movement of fuel to a safe position.

E.1 and E.2 In MODE 1, 2, 3, or 4, if the inoperable CREATCS trains cannot be restored to OPERABLE status within the required Completion Time, the unit must be placed in a MODE that minimizes the risk. 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 unit systems.If both CREATCS trains are inoperable in MODE 1, 2, 3, or 4, the CREATCS may not be capable of performing its intended function.

Therefore, LCO 3.0.3 must be entered immediately. The Completion Time is modified by a footnote that states an allowance to monitor the main control room temperature every hour and verify the main control room temperature is less than or equal to 90°F is permitted for up to four days in lieu of the immediate entry into LCO 3.0.3. If the main control room temperature exceeds 90°F, or the duration without a train of CREATCS being OPERABLE exceeds four days, immediate entry into LCO 3.0.3 is required. This provision is only applicable during modification activities planned for the upgrade of the main control room chillers beginning no earlier than July 1, 2023, and ending no later than December 31, 2024, provided the following compensatory measures are implemented as described in TVA letter CNL-20-012, dated May 19, 2020.

A temporary, non-safety related chiller system with a temporary DG to provide power to the temporary chiller system will be installed and operated as described in the LAR.

Instructions for operation of the temporary cooling equipment will be provided.

During replacement of the CREATCS chillers, TVA will employ a graded approach to defense-in-depth and protected equipment strategies

CREATCS B 3.7.11 Bases Watts Bar - Unit 2 B 3.7-62a Revision 47, Amendment 51, based on the operating status of the affected unit. The risk of the activity will be assessed and managed, including the use of physical barriers as needed. Additionally, TVA procedures preclude work on or near protected equipment and limit access to the area to emergency situations and non-intrusive monitoring of running equipment per operator rounds.

During replacement of the CREATCS chillers, no elective maintenance will be performed on TS related support equipment for the Operable CREATCS chiller except for any required TS SRs.

The purpose of the footnote is to ensure the MCR temperature is being controlled. The specified temperature limit of 90°F is above the normal operating temperature of the MCR (approximately 75°F), providing operational flexibility when implementing the mitigating actions. This temperature does not impact the operability of equipment or habitability of the MCR. The limit of 90°F maintains margin below the lowest specification for the MCR equipment cabinets of 104°F. Subsequent to immediate MCR temperature verification, the one-hour frequency is adequate given the indications available in the MCR. Main control room temperature data is measured and displayed from readily available equipment in the MCR and operators will have awareness of temperature trending relative to the 90°F limit.

F.1 If the Required Action and associated Completion Time of Condition D is not met in MODE 5 or 6, or during movement of irradiated fuel assemblies, with two CREATCS trains inoperable, action must be taken immediately to suspend activities that could result in a release of radioactivity that might require isolation of the control room. This places the unit in a condition that minimizes risk. This does not preclude the movement of fuel to a safe position.

SURVEILLANCE REQUIREMENTS SR 3.7.11.1 This SR verifies that the heat removal capability of the system is sufficient to remove the heat load assumed in the sizing calculations in the control room. This SR consists of a combination of testing and calculations. This is accomplished by verifying that the system has not degraded. The only measurable parameters that could degrade undetected during normal operation are the system air flow and chilled water flow rate. Verification of these two flow rates will provide assurance that the heat removal capacity of the system is still adequate. The Surveillance Frequency is controlled under the Surveillance Frequency Control Program.

CREATCS B 3.7.11 Bases Watts Bar - Unit 2 B 3.7-62b Revision 47, Amendment 51, REFERENCES

1.

Watts Bar FSAR, Section 9.4.1, Control Room Area Ventilation System.

2.

Watts Bar FSAR, Section 3.7.3.18, Seismic Qualification of Main Control Room Suspended Ceiling and Air Delivery Components.

3.

NRC Safety Evaluation dated February 12, 2004, for License Amendment 50.

4.

NRC Safety Evaluation dated May 5, 2021, for License Amendment 145

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