ML23304A268

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License Amendment Request to Revise the Ultimate Heat Sink Mission Time Pre Submittal Meeting on November 7, 2023
ML23304A268
Person / Time
Site: Vogtle  Southern Nuclear icon.png
Issue date: 11/07/2023
From:
Southern Nuclear Operating Co
To: John Lamb
NRC/NRR/DORL/LPL2-1
References
EPID L-2023-LRM-0097
Download: ML23304A268 (29)
v • d • e


Text

Vogtle Unit 1&2 Pre-Submittal Meeting November 7, 2023 License Amendment Request to Revise the Ultimate Heat Sink Mission Time

2 Meeting Purpose and Agenda The purpose for this meeting is to discuss proposed amendment request to revise the Ultimate Heat Sink Mission Time from 30 to 22 days and utilize available makeup systems to meet the Regulatory Guide 1.27 requirement to replenish cooling water for use 30 days post accident This meeting will cover the following topics:

  • Proposed change
  • Current Licensing Basis
  • Proposed Licensing Basis
  • Technical Evaluation
  • Regulatory Evaluation
  • Milestones

Proposed Change

4 Problem statement

  • Current Vogtle 1&2 Ultimate Heat Sink design and licensing bases assume one Emergency Diesel Generator (EDG) will be shut down 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> post-accident to ensure adequate inventory exists with four NSCW fans in operation for the 30-day analysis period per Reg Guide 1.27. The NRC issued Vogtle a violation concerning operational readiness of the EDGs after one EDG is secured to preserve Nuclear Service Cooling Water (NSCW) mission time capabilities without offsite power available.
  • Running both EDGs and NSCW trains after the first 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> would ensure operational readiness of both EDGs for the duration of the 30-day period.

Proposed Resolution Change the licensing basis to allow both EDGs and NSCW trains to run continuously after the first 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> post-accident and utilize the available water sources of well water and river water to replenish the NSCW basins to ensure cooling water supply for 30 days in accordance with Regulatory Guide 1.27.

Current Design and Licensing Basis

6 Current Design and Operation

  • Current plant analyses assume that two EDGs and NSCW trains are in operation for the first 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> post-accident, after which one EDG and NSCW train is secured.
  • The NSCW basins were sized to provide a 30-day supply of cooling water post-accident, without the use of makeup.
  • In order to meet these requirements for 30 days post-accident NSCW inventory, the second EDG is shut down 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> post accident.

7 Existing Technical Specification Bases 3.7.9 (Excerpts)

Background

The combined storage capacity of tower basins provides greater than a 30-day cooling water supply assuming the worst combination of meteorological conditions and accident heat loads which maximize the tower heat load, basin temperature, and evaporative losses Applicable Safety Analyses The UHS is designed in accordance with Regulatory Guide 1.27 (Ref. 2), which requires a 30-day supply of cooling water in the UHS LCO The UHS is required to be OPERABLE and is considered OPERABLE if it contains a sufficient volume of water at or below the maximum temperature that would allow NSCW to operate for at least 30 days following the design basis LOCA without the loss of net positive suction head (NPSH), and without exceeding the maximum design temperature of the equipment served by the NSCW.

8 Existing Technical Specification Bases 3.7.9 (Excerpts)

Surveillance Requirements SR 3.7.9.1 This SR verifies that adequate long term (30 day) cooling can be maintained.

SR 3.7.9.2 This SR verifies that the NSCW System is available to cool the CCW System to at least its maximum design temperature with the maximum accident or normal design heat loads for 30 days following a Design Basis Accident.

9 FSAR Sections Associated with Proposed Change

  • FSAR 2.4.11.5 Plant Requirements
  • FSAR 2.4.11.6 Heat Sink Dependability Requirements

10 Existing FSAR Sections Related to Proposed Change FSAR 9.2.5 Ultimate Heat Sink The Ultimate Heat Sink(UHS) for VEGP is NSCW towers. Two 100% capacity redundant NSCW towers are provided for each generating unit, one tower associated with each train of the NSCW system. Each NSCW tower consists of a basin which contains the ultimate heat sink water and an upper structure in which the NSCW heat loads are transferred to the atmosphere. The combined storage capacity of the two tower basins per unit will meet the intent of the short-term storage requirements without makeup in conformance with Nuclear Regulatory Commission (NRC)

Regulatory Guide 1.27.

A. UHS designed so that a single failure coincident with a loss of offsite power does not result in inadequate core cooling or prevent a safe shutdown under extreme meteorological conditions.

B. Regulatory Guide 1.27 recommends the UHS be capable of providing sufficient cooling for at least 30 days, with no makeup water, assuming two-train operation for 1 day and single-train operation for the remaining 29 days. System design based on maximum conditions of dry and wet bulb temperatures as they affect peak basin temperature, tower evaporation losses, and basin capacity.

C. The ultimate heat sink is protected from freezing.

Proposed Design and Licensing Basis

12 Proposed Licensing Basis

  • The proposed configuration will allow for both EDGs and NSCW trains to remain in operation after the first 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> post-accident.
  • This change would reduce the inventory of the NSCW cooling tower basin from 30 days to 22 days
  • After 22 days post-accident, available makeup cooling water would be utilized from the sources, well water and river water makeup system, to ensure there is sufficient water available to the equipment serviced by the NSCW cooling towers.
  • The proposed configuration continues to ensure cooling water is available 30 days post-accident, using backup system replenishment in accordance with Regulatory Guide 1.27.

13 Proposed Licensing Basis

  • Analyses show that when both EDGs and NSCW trains are operated continuously post-accident, the NSCW system basins have a 22 day inventory of cooling water.
  • Use of the NSCW tower basins combined with replenishment from well water pumps, provide a 30 day inventory to permit safe shutdown.
  • TS Bases 3.7.9 and FSAR Chapters provided would be updated with new analyses results to allow NSCW tower basins to be supplemented with makeup from well water and river water to provide a combined 30-day short term cooling water supply as required by RG 1.27.

The proposed activity would result in a departure from a method of evaluation, as described in the Updated FSAR used in establishing the design bases / safety analyses and will require NRC approval prior to implementation

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Technical Evaluation

18 Technical Evaluation

Updated analyses show that there will be at least 22 days of cooling water available in the NSCW basin post-accident when both EDGs are in service. Makeup is therefore required to meet the 30-day requirement. No methodology changes were involved.

Updated analyses show that Four NSCW cooling tower fans must be in operation for a minimum of 5 days (120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br />) post-accident to maintain the current design basis maximum basin temperature.

Updated analyses show that there is sufficient fuel oil to meet the 7-day requirement provided operator actions reduce electrical load on the EDGs.

An EDG loading profile will need to be used to achieve the 7-day requirement, which will involve changes to operating procedures.

Regulatory Evaluation

20 Regulatory Requirements Regulatory Guide 1.27 The capacity of the UHS should be sufficient to provide cooling for the time necessary to evaluate the situation and take corrective action. A period of 30 days is considered adequate for these purposes. In addition, procedures should be available for ensuring the continued capability of the UHS beyond 30 days. A capacity of less than 30 days may be acceptable if it can be demonstrated that replenishment can be effected to ensure the continuous capability of the UHS to perform its safety functions, taking into account the availability of replenishment equipment and limitations that may be imposed following an accident or severe natural event.

Replenishment sources - There are various replenishment sources in place that can be established to ensure the continuous capability of the NSCW system to perform its safety functions:

21 Regulatory Requirements Regulatory Guide 1.27 (continued)

Replenishment Sources-Well Water Makeup: Normal makeup water for the nuclear service cooling water is provided by wells drilled into the Tuscaloosa aquifer, which has enough water yield capacity to meet the makeup requirements for emergency conditions. The aquifer has sufficient capacity to supply the necessary inventory requirements to support days 22-30 and (2) the well water pumps have greater capacity than the NSCW evaporative losses (i.e., replenish inventory).

The well water pumps would be used within the 22-day span to refill the NSCW basin capacity.

The well water pumps are not powered by safety related buses. However, their power supplies are tied to Station Auxiliary Transformers (SATs). These SATs are connected to Plant Wilson, which can provide support through black start diesel generators to provide power to the Well Water pumps The proposed 22 days is sufficient time to establish the power to the pumps from Plant Wilson or provide power by alternative means

22 Regulatory Requirements Regulatory Guide 1.27 (continued)

Replenishment Sources-River Water Makeup: The river intake makeup water facilities are provided as a secondary backup source for the makeup water system. The river has sufficient capacity to supply the necessary inventory requirements to support days 22-30 and river water pumps have greater capacity than the NSCW losses (i.e., replenish inventory).

Four River water pumps powered from a split 4.16Kv bus, two pumps per bus. One bus is normally powered from Unit 2. Another bus(B) is normally powered from Unit 1. A crosstie breaker allows the split bus to be powered completely by either unit.

These power supplies are tied to Station Auxiliary Transformers (SATs). These SATs are connected to Plant Wilson, which can provide support through black start diesel generators to provide power to the River Water pumps.

The proposed 22 days is sufficient time to establish the power to the pumps from Plant Wilson or provide power by alternative means.

23 Regulatory Requirements Acceptance criteria:

  • GDC 5, Sharing of Structures, Systems, and Components
  • GDC 45, Inspection of Cooling Water System, and
  • GDC 46, Testing of Cooling Water System

24 Regulatory Requirements Acceptance criteria (continued):

  • 10 CFR 100.10(c) Physical characteristics of the site, including seismology, meteorology, geology, and hydrology
  • 10 CFR 100.23(d), Geologic and seismic siting factors No changes impacting either of these regulatory requirements.

25 Licensing Basis

  • Environmental Protection Plan has been reviewed is not impacted.
  • Safety Design basis will continue to be met, due to continued conformance with RG 1.27, GDCs and other regulatory requirements.

26 Precedent

  • Safety Evaluation by the Office of Nuclear Reactor Regulation related to Amendment No 93 (Operating License NPF-41), Amendment No. 81 (Operating License NPF-41),and Amendment No. 81 (Operating License NPF-41), Palo Verde Nuclear Generating Station Unit Nos. 1, 2, and 3, June 14, 1995, ML021710106
  • NUREG-1137, Safety Evaluation Report Related to the operation of VEGP Units 1 and 2, June 1985 (original SER discusses a 26.7-day UHS supply)

Milestones

28 Milestones

  • Submit LAR by end of 1Q2024
  • Implementation would occur within 120 days of NRC approval.

Questions?

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