ML24044A087

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TVA Slides - Watts Bar Nuclear Plant Pre-Submittal Meeting for License Amendment Request to Revise TS 3.7.11, Main Control Room Area Chilled Water System
ML24044A087
Person / Time
Site: Watts Bar  Tennessee Valley Authority icon.png
Issue date: 02/14/2024
From: Jim Barstow
Tennessee Valley Authority
To: Kimberly Green
Plant Licensing Branch II
Green K
References
Download: ML24044A087 (1)
v • d • e


Text

License Amendment Request (LAR)

Watts Bar Nuclear Plant (WBN)

Pre-submittal Meeting for License Amendment Request to Revise TS 3.7.11, Control Room Area Chilled Water System

February 15, 2024 Agenda

  • Introduction
  • Background
  • System Description
  • Description of the Proposed Change
  • Reason for the Proposed Change
  • Basis for the 96-hour Completion Time
  • Technical Evaluation
  • Precedent
  • Schedule Milestones
  • Closing Remarks

2 Introduction

  • The purpose of this meeting is to discuss a proposed license amendment request (LAR) for the Watts Bar Nuclear Plant (WBN)

Units 1 and 2.

  • The pr oposed 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 are initiated immediately. The mitigation actions include verifying control room temperature is less than or equal to 90°F and the current installation of a non-s afety related chiller with a dedicated diesel generator to provide power to the non-s afety r elated system.

l 3

Background

  • 5/19/2020 - TVA submits a LAR (ML20140A342) for WBN Units 1 and 2 to add a one-time change of a footnote to the Completion Time for TS 3.7.11 Required Action A.1 to allow one CREATCS train to be inoperable for up to 60 days while performing modifications to the WBN Units 1 and 2 Main Control Room (MCR)

CREATCS chillers. The proposed amendment also added a one-time change of a footnote to the Completion Time for Required Action E.1 to allow delayed entry into TS Limiting Condition for Operation (LCO) 3.0.3 for up to 4 days (96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br />) in the event that both CREATCS trains are inoperable during the modifications to the CREATCS chillers. LAR included technical information on the MCR CREATCS replacement project including the temporary chilled water system to be utilized during the MCR CREATCS replacement project.

l 4 Background (contd)

  • 2/37/2023 - TVA submits an expedited LAR (ML23058A447) to revise the timeframe of the above footnotes to begin no earlier than July 1, 2023, and end no later than December 31, 2024.
  • However, installation of the MCR chillers is on hold as a result of operational issues identified on the similarly designed Shutdown Board Room (SDBR) chiller during post installation testing. TVA is currently working with the vendor to develop corrective actions to ensure reliable operation of these chillers once permanently installed in the plant.

l 5 Background (contd)

  • As described in the original LAR, the RAI response, the NRC regulatory audit and the original NRC safety evaluation (SE), a non-safety related chiller has been installed and is being used to support MCR cooling during the CREATCS chiller replacements. This system is capable of providing adequate cooling to maintain the MCR within its normal temperature band. TVA plans to keep a non-safety related chiller available for use to provide backup cooling in the event one or both CREATCS become inoperable.

l 6

System Description

  • The CREATCS provides temperature control for the control room following isolation of the control room. The CREATCS consists of two independent and redundant trains that provide cooling of recirculated control room air.
  • Each train consists of an air handling unit (AHU), water chiller, chilled water pump, and associated piping, ductwork, instrumentation, and controls to provide for control room temperature control.
  • The CREATCS is a subsystem providing air temperature control for the control room.
  • Further description of the CREATCS is provided in Section 3.1 to the initial LAR (ML20140A342).

l 7

System Description

  • A description of the non-safety related chiller is provided in Section 3.2 to the initial LAR, the TVA response to EMIB-RAI-1, the initial NRC SE, and the NRC regulatory audit summary. The major components of the non-safety related chiller include the following:

Air cooled chilled water package Chilled water pump Power supply, cables, and connections Chilled water supply and return hoses Demineralized water source Engineered penetrations with isolation valves Backup diesel generator (DG) with fuel tank

l 8 System Description (contd)

  • The non-safety related chiller was initially planned to be a temporary system during the MCR CREATCS chiller project. However, TVA has decided to retain the non-safety related chiller. Therefore, the hoses, pipe, and fittings for the non-safety related chiller will remain available. The component ratings for these connections bound the maximum system pressure of the non-safety related chiller. Also, the non-safety related chiller is not a high energy line system, and evaluation and qualification of the system piping for pipe rupture and pipe whip is not required.
  • The non-safety related chiller piping system has been evaluated for internal pressure, deadweight, and seismic loading conditions, and meets the requirements of Seismic Category I(L), which is defined in Watts Bar Updated Final Safety Analysis Report (UFSAR) Section 3.2.1.

l 9 System Description (contd)

  • The initial NRC SE also describes how the piping and support including the weld as well as the valve were seismically analyzed. Also, as noted in the initial NRC SE, the flooding effect of potential pipe leakage from the non-safety related chiller water system in the Main Control Room Habitability Zone (MCRHZ) is bounded by the current flooding analysis.
  • As noted in the initial NRC SE, the non-safety related chiller working in conjunction with each air handling unit (AHU) is capable of meeting the cooling requirements of the MCRHZ during plant normal operations.
  • The power supplies for the non-safety related chiller (including the backup DG) are described in Section 3.1.3 of the initial NRC SE, which notes that the dedicated DG fuel oil tanks capacity provides a 12-hour run time for the chiller skid without fuel oil replenishment, which is an adequate time to take replenishing measures from alternate sources.

l 10 System Description (contd)

  • The location of the non-safety related chiller is described in Section 3.1.4 of the initial NRC SE, which notes that in the event that non-safety-related 480V AC source is lost and the skids DG is required to operate to power the non-safety related chiller, the distance of the skid from the fresh air intakes that any DG exhaust fumes emitted from the skid would be sufficiently dilute so as not to provide a threat to MCR habitability or auxiliary building accessibility.
  • The non-safety related chiller will be controlled under a procedurally controlled T-mod.

l 11 Description of the Proposed Change

  • The proposed change revises the Required Actions applicable when two CREATCS trains are inoperable. The proposed Required Actions require immediate initiation of an action to implement mitigating actions to ensure control room temperature will not exceed 90° F, or if one CREATCS train is not restored to operable status within 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> while in Modes 1, 2, 3, or 4, the unit must be in Mode 3 in 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and Mode 5 in 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. In Mode 5 or 6, or during movement of recently irradiated fuel assemblies, immediate suspension of movement of recently irradiated fuel assemblies is required.

l 12 Description of the Proposed Change (contd)

l 13 Description of the Proposed Change (contd)

l 14 Description of the Proposed Change (contd)

(Bases Markups)

l 15 Description of the Proposed Change (contd)

l 16 Description of the Proposed Change (contd)

l 17 Description of the Proposed Change (contd)

l 18 Reason for the Proposed Change

  • The current WBN 1 and 2 TS 3.7.11 requires an immediate disruption of plant operations in the event both CREATCS trains become inoperable. Allowing for 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> to restore an inoperable CREATCS train to operable status minimizes the potential safety consequences and operational risks associated with the disruption of plant operations. The basis for the 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> is discussed further in this presentation.
  • The proposed change adds a new Condition D for two CREATCS trains inoperable which allows 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 by implementing mitigating actions (including the use of a non-safety related chiller) and verifying control temperature is less than or equal to 90° F every hour (consistent with the current temporary measures for the MCR chiller replacement project).

l 19 Basis for the 96-hour Completion Time

  • In Section 3.4.1.2 of the initial NRC SE, the NRC evaluated the acceptability of a 96-hour completion time with both CREATCS trains inoperable.

The NRC SE states:

The proposed footnote states that operators will monitor the MCR temperature every hour and verify that the temperature is less than or equal to 90° F, for up to 4 days in lieu of immediate entry into LCO 3.0.3. The temperature limit for MCR equipment operability is 104° F, and the normal MCR operating temperature is 75 °F. The licensee provided a calculation of the time that it will take for the MCR and surrounding areas to heat up before the heat-up starts to affect the operability of equipment and challenge operator comfort. The licensee suggests that the calculated time is sufficient enough that operators will be well aware of the heat-up prior to reaching 90 ° F, specifically stating, the MCR 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.

l 20 Basis for the 96-hour Completion Time

  • The NRC staff reviewed TVAs proposed operator actions related to the proposed change to Watts Bar, Units 1 and 2, TS 3.7.11, Condition E, and finds them to be acceptable because (1) actions that the operators would perform for a dual-unit shutdown are the same as any entry into TS LCO 3.0.3, (2) there are existing actions that the operators may take to remove heat from the MCR, and (3) there are AOPs to allow for continuous control of the MCR in the case that the MCR temperature cannot be controlled.

l 21 Technical Evaluation

  • The non-safety related chiller to be used for temporary cooling of the MCR CREATCS exceeds the minimum capacity of 150 tons noted in the NRC Audit Summary. The cooling load of the area served by the MCR CREATCS is 85 tons, which is significantly lower than the rated capacity of the non-safety related chiller.
  • The non-safety related chiller has previously been utilized during replacement of the SDBR Chiller B and the system proved reliable during replacement of that safety-related chiller. The cooling load of the area served by the SDBR chilled water system is 116 tons, which is also significantly lower than the rated capacity of the non-safety related chiller. Thus, the significantly higher rated capacity of the non-safety related chiller ensures that design conditions are maintained during normal and accident modes of operation.

l 22 Technical Evaluation

  • Also, as described in Section 3.4.1.2 to the NRC SE, there are existing actions operators may take should the operators attempt to remove heat from the MCR. For example, the actions for smoke removal would be useful in removing heated air from the MCR.
  • The compensatory measures to be taken when a unit enters TS 3.7.11.D.3 are described in the TS Bases and plant procedures.
  • Thus, the proposed 96-hour Completion Time of new Required Action D.3 is considered adequate given the mitigating actions and the low probability of an accident that would require operation of the CREATCS, 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.

l 23 Precedent

  • Previous WBN LAR approved by NRC (ML21078A484) for a one-time change of a footnote to the Completion Time for WBN Units 1 and 2 TS 3.7.11, Required Action E.1 to allow delayed entry into TS LCO 3.0.3 for up to 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> in the event that both CREATCS trains are inoperable during the modifications to the CREATCS chillers.
  • 2017 submittal by Constellation (then Exelon) for Byron and Braidwood Nuclear Stations, approved in 2018 (ML18054B436)
  • 6/19/2023 submittal by Duke Energy for Catawba (ML23170A015), currently under NRC review

l 24

Precedent

  • Consistent with Standard and Other WBN TSs:
  • Improved Standard TSs allow a Completion Time to restore one inoperable control room cooling train, with two inoperable:

NUREG-1432, ISTS for CE Plants (24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> allowance)

NUREG-1433, ISTS for GE BWR/4 Plants (72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> allowance)

NUREG-1434, ISTS for GE BWR/6 Plants (7 day allowance)

  • Current WBN TSs provide an extended Completion Time for two or more inoperable trains:

TS 3.3.3, Post Accident Monitoring Instrumentation TS 3.4.15, Reactor Coolant System (RCS) Leakage Detection

l 25 Instrumentation

Schedule Milestones

  • TVA to submit LAR to NRC by April 15, 2024.
  • Request NRC approval within 1-year from submittal.
  • 60- day implementation following NRC approval.

l 26

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