RS-21-050, Response to Request for Additional Information (RAI) Regarding Request for License Amendment Regarding Ultimate Heat Sink (EPID-L-2020-LLA-0165)

Response to Request for Additional Information (RAI) Regarding Request for License Amendment Regarding Ultimate Heat Sink (EPID-L-2020-LLA-0165)

ML21106A176
Person / Time
Site:	LaSalle
Issue date:	04/16/2021
From:	Demetrius Murray Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
EPID-L-2020-LLA-0165, RS-21-050
Download: ML21106A176 (6)

Text

Exelon Generation 4300 Winfield Road Warrenville, IL 60555 www.exeloncorp.com 10 CFR 50.90 RS-21-050 April 16, 2021 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 LaSalle County Station, Units 1 and 2 Renewed Facility Operating License Nos. NPF-11 and NPF-18 NRC Docket Nos. 50-373 and 50-374

Subject:

Response to Request for Additional Information (RAI) Regarding Request for License Amendment Regarding Ultimate Heat Sink (EPID-L-2020-LLA-0165)

References:

1. Letter from D. Murray (Exelon Generation Company, LLC) to U.S. Nuclear Regulatory Commission (NRC), "Request for a License Amendment to LaSalle County Station , Units 1 and 2, Technical Specification 3.7.3, 'Ultimate Heat Sink,"' dated July 17, 2020 (ML20204A775)

2. Letter from U.S. Nuclear Regulatory Commission to B. Hanson (Exelon Generation Company, LLC), "LaSalle County Station, Units 1 and 2 -

Supplemental Information Needed for Acceptance of Requested Licensing Action Regarding Request for a License Amendment to Technical Specification 3.7.3, 'Ultimate Heat Sink,"' dated August 27, 2020 (ML20239A726)

3. Letter from D. Murray (Exelon Generation Company, LLC) to U.S. Nuclear Regulatory Commission (NRC), "Supplement to the Request for License Amendment to LaSalle County Station, Units 1 and 2, Technical Specification 3.7.3, 'Ultimate Heat Sink,"' dated September 11, 2020 (ML20259A454)

4. Letter from D. Murray (Exelon Generation Company, LLC) to U.S. Nuclear Regulatory Commission (NRC), "Supplement Regarding Request to Withhold Information Related to License Amendment to Revise Technical Specification 3.7.3, 'Ultimate Heat Sink,"' dated October 22, 2020 (ML20259A454)

5. Letter from U.S. Nuclear Regulatory Commission (B. Vaidya) to J. Taken (Exelon Generation Company, LLC), "LaSalle Units 1 and 2 - Request for Additional Information (RAI) RE: Request for License Amendment Regarding Ultimate Heat Sink, (EPID-L-2020-LLA-0165)," dated March 8, 2021.

U.S. Nuclear Regulatory Commission April 16, 2021 Page 2

6. Letter from D. Murray (Exelon Generation Company, LLC) to U.S. Nuclear Regulatory Commission (NRC), "Response to Request For Additional Information (RAI) Regarding Request For License Amendment Regarding Ultimate Heat Sink (EPID-L-2020-LLA-0165)," dated April 7, 2021 (ML21097A247)

7. Letter from U.S. Nuclear Regulatory Commission (B. Vaidya) to J. Taken (Exelon Generation Company, LLC), "LaSalle Units 1 and 2 - Request for Additional Information (RAI) RE: Request for License Amendment Regarding Ultimate Heat Sink, (EPID-L-2020-LLA-0165)," dated March 18, 2021.

In Reference 1, Exelon Generation Company, LLC (EGC) submitted license amendment request (LAR) to revise Technical Specification (TS) 3.7.3, "Ultimate Heat Sink," to expand the already-approved diurnal curve. In References 2 through 4, EGC submitted supplemental information necessary for the Nuclear Regulatory Commission (NRC) to complete its review of Reference 1.

In Reference 5, the NRC identified additional information needed to complete its review of Reference 1. EGC response to Reference 5 was provided in Reference 6.

In Reference 7, the NRC identified additional information needed to complete its review of Reference 1. A clarification call was held between NRC and EGC to ensure a mutual understanding of the additional information required.

The attachment to this letter contains the response to the request for additional information identified in Reference 7.

EGC has reviewed the information supporting a finding of no significant hazards consideration and the environmental consideration provided to the NRC in Reference 1. The supplemental information provided in this letter does not affect the bases for concluding that the proposed license amendment does not involve a significant hazards consideration. Furthermore, the supplemental information provided in this letter does not affect the bases for concluding that neither an environmental impact statement nor an environmental assessment needs to be prepared in connection with the proposed amendment.

There are no regulatory commitments contained in this letter.

Should have any questions regarding this submittal , please contact Jason Taken at 630-657-3660.

U.S. Nuclear Regulatory Commission April 16, 2021 Page 3 I declare under penalty of perjury that the foregoing is true and correct. Executed on the 161h day of April 2021.

Respectfully,

¥¥ Dwi Murray Sr. Manager - Licensing Exelon Generation Company, LLC

Attachment:

Response to Request for Additional Information cc: NRC Regional Administrator, Region Ill NRC Senior Resident Inspector - LaSalle County Station NRC Project Manager, NRR - LaSalle County Station Illinois Emergency Management Agency - Division of Nuclear Safety

ATTACHMENT LaSalle County Station, Units 1 and 2 Renewed Facility Operating License Nos. NPF-11 and NPF-18 NRC Docket Nos. 50-373 and 50-374 Response to Request for Additional Information

ATTACHMENT Response to Request for Additional Information Request for Additional Information: RAl-STSB-1 BASIS FOR THE REQUEST:

On July 17, 2020, Exelon Generation Company, LLC (the licensee) requested a change to the Technical Specifications (TS) of LaSalle County Station , Units 1 and 2.

In their request, the licensee proposed to delete the Ultimate Heat Sink (UHS) bottom elevation limit from TS 3.7 .3 Condition A and remove the associated TS Surveillance Requirement (SR) 3.7 .3.3. The licensee justified this change by stating:

The current TS SR 3.7.3.3 verifies Core Standby Cooling System (CSCS) pond bottom elevation is less than or equal to 686.5 feet. The proposed change would delete TS SR 3.7.3.3 because the requirement to ensure adequate long term cooling can be maintained through verification of average sedimentation level as proposed in TS SR 3.7.3.2. The use of average sedimentation depth of no greater than 6 inches ensures that a sufficient UHS volume remains for use during a design basis accident.

REGULATORY ANALYSIS BASIS:

Title 10 of the Code of Federal Regulations (CFR) Part 50 .36(c)(3), describes SRs as requirements relating to test, calibration , or inspection to assure that the necessary quality of systems and components is maintained , that facility operation will be within safety limits, and that the limiting conditions for operation (LCO) will be met. The request above is needed to assure appropriate parameters are verified and LCO 3.7.3, Core Standby Cooling System pond operable, will be met.

REQUEST FOR ADDITIONAL INFORMATION:

RAI STSB-1 Part 1 :

It is unclear from the request how the sedimentation level correlates with UHS water volume. Please provide an explanation on how the necessary UHS water volume, an essential parameter used in the safety analysis (Updated Safety Analysis Report (UFSAR) Section 9.2.6),

will be ensured by only verifying average sedimentation .

EGC Response:

The UHS water volume noted in UFSAR Section 9.2 .6 is the general volume of the UHS which will not change. The amount of water credited for cooling in the event of an accident currently assumes the presence of a uniform silt layer of 1.5 feet in depth. The water volume that would be displaced by the sediment is not included in the available volume of water when evaluating cooling capabilities of the UHS. (Reference Page J13 of Calculation L-002457, Revision 8

[ADAMS Accession No. ML15113B045])

A sensitivity study to analyze the impact of the reduced UHS volume reviewed cases with varying sedimentation depths to verify the corresponding UHS effective volumes and their effect on maximum plant inlet water temperature. The three most recent siltation surveillances from Page 1 of 2

ATTACHMENT Response to Request for Additional Information 2016, 2018, and 2020 indicate that the average siltation depth is less than six inches. Since the actual volume of sediment displacing water in the UHS is always below six inches average sediment height, the sensitivity cases bound actual sediment depths in the UHS. The resultant maximum plant inlet water temperature remains bounded by the Ultimate Heat Sink Analysis in Calculation L-002457, Revision 8.

Since the cooling capability of the UHS was evaluated assuming a volumetric reduction due to displacement by a uniform layer of silt, any survey showing siltation levels less than what is assumed in the bounding analysis will provide sufficient evidence that the necessary UHS water volume is present.

RAI STSB-1 Part 2:

In addition, the current SR 3.7.3.3, which is proposed for removal, validates the lower elevation and would seem to establish a bottom, above which sediment may be measured to determine available water volume in the UHS . Please provide a detailed justification for removing SR 3.7.3.3, including how the UHS volume is validated without that established lower elevation .

EGC Response:

The volume of the UHS was calculated using the results of hydrographic surveys performed in November 1997 and February 1998. These hydrographic surveys produced a topographical map of the UHS with contour lines of constant elevation at one-foot intervals. This map was used to calculate total volume by considering the volume as being made up of a total of 15 horizontal slices, with each slice being 1 foot thick. A Computer Aided Design program was used to calculate the area associated with the top and bottom of each slice. When the surveys were performed , the actual sediment levels were considered as the "bottom" of the UHS, effectively re-baselining the UHS volume. The level of the bottom of the UHS varies, becoming progressively deeper as it approaches the lake intake structure. While SR 3.7 .3.3 reflects a reference level of the bottom in the shallow end of the UHS, it does not provide a baseline elevation for sediment accumulation in the deeper parts of the UHS.

Subsequent hydrographic surveys take soundings of the bottom at multiple locations which are referenced to the baseline study and yield the localized depth of accumulated sediment as well as the average sediment depth. Data from the surveys is used to determine the volume and that volume is validated against the bounding conditions of the design analysis and baseline surveys. As stated in Technical Specification Bases for SR 3.7.3.2, sediment level is determined by a series of sounding cross-sections compared to as-built soundings.

Therefore, SR 3.7.3.3 provides marginal value in assessment of UHS volume and capability and is proposed to be deleted since the average siltation level provides the available UHS volume required for heat removal of design basis loads.

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