ML14287A478

Request for Additional Information Regarding Request to Revise Ultimate Heat Sink Temperature Limits

ML14287A478
Person / Time
Site:	LaSalle
Issue date:	11/14/2014
From:	Blake Purnell Plant Licensing Branch III
To:	Pacilio M Exelon Generation Co
Blake Purnell, NRR/DORL 415-1380
References
Download: ML14287A478 (7)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 November. 14, 2014 Mr. Michael J. Pacilio Senior Vice President Exelon Generation Company, LLC President and Chief Nuclear Officer (CNO)

Exelon Nuclear 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

LASALLE COUNTY STATION, UNITS 1 AND 2- REQUEST FOR ADDITIONAL INFORMATION REGARDING REQUEST TO REVISE ULTIMATE HEAT SINK TEMPERATURE LIMITS (TAC NOS. ME9076 AND ME9077)

Dear Mr. Pacilio:

By application dated July 12, 2012, as supplemented by letters dated September 17, 2012, January 18, February 11, and October 4, 2013, and February 20, 2014, Exelon Generation Company, LLC submitted a license amendment request to the U.S. Nuclear Regulatory Commission (NRC) for LaSalle County Station (LSCS), Units 1 and 2 (Agencywide Documents Access and Management System Accession Nos. ML12200A330, ML122690041, ML13022A476, ML13042A405, ML13282A339, and ML14066A250, respectively). The proposed amendment would modify Technical Specification 3.7.3, "Ultimate Heat Sink [UHS],"

by changing the maximum allowable temperature of the UHS from a fixed limit of 101.25 degrees Fahrenheit (°F) to a variable limit between 101.25 and 104 oF depending on the time of day. The NRC staff is reviewing the submittal and has determined that additional information is needed to complete its review.

A response to the enclosed request for additional information should be provided by December 12, 2014. This request was discussed with Ms. Lisa Simpson and Mr. David Gullott of your staff on October 29, 2014.

M. Pacilio Should you have any questions, please contact me at 301-415-1380 or by email at blake. purnell@nrc.gov.

Blake Purnell, Project Manager Plant Licensing 111-2 and Planning and Analysis Branch Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-373 and 50-37 4

Enclosure:

Request for Additional Information cc w/encl: Listserv

REQUEST FOR ADDITIONAL INFORMATION (RAI)

LICENSE AMENDMENT REQUEST TO REVISE ULTIMATE HEAT SINK TEMPERATURE LIMITS LASALLE COUNTY STATION, UNITS 1 AND 2 DOCKET NOS. 50-373 AND 50-374 By application dated July 12, 2012, as supplemented by letters dated September 17, 2012, January 18, February 11, and October 4, 2013, and February 20, 2014, Exelon Generation Company, LLC (the licensee) submitted a license amendment request (LAR) to the U.S.

Nuclear Regulatory Commission (NRC) for LaSalle County Station (LSCS), Units 1 and 2 (Agencywide Documents Access and Management System (ADAMS) Accession Nos. ML12200A330, ML122690041, ML13022A476, ML13042A405, ML13282A339, and ML14066A250, respectively). The proposed amendment would modify Technical Specification (TS) 3.7.3, "Ultimate Heat Sink [UHS]," by changing the maximum allowable temperature of the UHS from a fixed limit of 101.25 degrees Fahrenheit (°F) to a variable limit between 101.25 and 104 oF depending on the time of day. The NRC staff is reviewing the submittal and has determined that additional information is needed to complete its review.

RAI1

Background

NRC Regulatory Guide (RG) 1.27, "Ultimate Heat Sink for Nuclear Power Plants," Revision 2 states: "The meteorological conditions resulting in minimum water cooling should be the worst case combination of controlling parameters, including diurnal variations where appropriate, for the critical time period(s) unique to the specific design of the sink." In its October 4, 2013, letter, the licensee stated that the UHS analysis for the proposed TS uses limiting environmental data and is consistent with RG 1.27, Revision 2.

Concern The NRC staff is aware of a phenomenon at LSCS, called the midnight thermal transient, where the LSCS cooling lake temperature peaks around midnight. In addition, the staff notes that the current TS 3.7.3 temperature limit for the UHS was exceeded on August 12, 2010. These events were not specifically discussed in the October 4, 2013, letter, so it is not clear that the worst-case weather conditions per RG 1.27, Revision 2, including wind speed and direction and other factors, are accounted for in the LAR. The staff is concerned that high water temperatures that could result from a midnight thermal transient would be a worst-case situation and would need to be considered in the peak temperature analysis for the UHS. The staff also needs to understand the conditions under which high LSCS cooling lake temperatures occur. The staff notes that the licensee's internal report for the root cause investigation of the August 12, 2010, event includes some of the information requested below.

Request

a. Provide information on the midnight thermal transient and other events which resulted in high LSCS cooling lake temperatures. Include details of meteorological data, environmental conditions, temperature rise, and other factors at time of occurrence that would explain the phenomena or events.

b. Describe how the midnight thermal transient and other events which resulted in high LSCS cooling lake temperatures are addressed in the analysis for this LAR.

RAI2

Background

The application states that the LAKET-PC computer program is used to model the LSCS UHS for the design-basis event. The analysis of the UHS using LAKET-PC is described in LSCS Design Analysis L-002457, "LaSalle County Station Ultimate Heat Sink Analysis," Revision 8, which was provided with the licensee's February 20, 2014, letter. Section 2.3, "Limitations" (p. 16), of L-002457 states: "The results of this calculation are limited by the accuracy of the LAKET-PC program and models inherent in the code (see Ref. 5.14, for a comparison of the predictions of the LAKET program against lake intake temperatures observed in August 1989 at the LaSalle Station)."

Concern The application does not provide sufficient information on how the LAKET-PC computer code was validated for use at LSCS.

Request Provide the comparison study listed as Reference 5.14 in LSCS Design Analysis L-002457, Revision 8, or other documentation which compares the results of the LAKET-PC computer code with actual data for the LSCS cooling lake.

RAI3

Background

Water bodies, particularly cooling reservoirs and ponds, are often stratified and behave differently from non-stratified bodies. The licensee's analysis in LSCS Design Analysis L-002457, Revision 8, included a calculation to determine whether the flows in the UHS were non-stratified, which is a condition for use of the LAKET model.

Concern The NRC staff needs to evaluate the bases for the calculation used to determine if there is potential stratification of the cooling pond. The information provided with the LAR is not sufficient to support the staff's evaluation.

Request

a. Provide the Mechanical Engineering Standard MES-11.1 [Reference N5.7 in LSCS Design Analysis L-002457, Revision 8] or other documents explaining the basis for determining the stratification of a lake as described in Section N2.0.1, "Lake Stratification," of Attachment N, to LSCS Design Analysis L-002457, Revision 8.

b. Provide elevation drawings showing the flow paths from the UHS to the residual heat removal service water pumps and the diesel generator cooling water pumps, including bypass flow around the intake screens and strainers.

RAI4

Background

The licensee used a combination of onsite and offsite meteorological data to determine the periods of worst UHS pond performance for temperature and evaporation. NUREG-0693, "Analysis of Ultimate Heat Sink Cooling Ponds," published November 1980 (ADAMS Accession No. ML12146A144), describes a procedure for determining the similarity of onsite and offsite meteorological records and, if necessary, a correction factor to be applied to the calculations.

Concern The NRC staff needs to evaluate consistency with NUREG-0693 for the use of offsite meteorological data from distant stations in Peoria and Springfield, Illinois, for the UHS analyses, and whether correction factors need to be applied to the results.

Request Provide the basis for concluding that use of offsite meteorological data from Peoria, Illinois, is more conservative for UHS temperature predictions than onsite data. Clarify whether meteorological data from Springfield, Illinois, were used in the analyses for the LAR, and, if so, whether these data are conservative for the stated purposes.

RAIS

Background

The NRC staff needs to assess the data used in the licensee's UHS analyses with respect to the use of meteorological stations far from the LSCS site. In addition, the staff needs to assess the validity of certain assumptions used in the UHS analysis.

Concern The NRC staff is conducting a confirmatory analysis to assess the adequacy of the licensee's selection of meteorological data, plug flow modeling, and use of certain assumptions (e.g.,

stratification) in the UHS analysis.

Request

a. Provide the meteorological data used in the UHS analysis for this LAR (LSCS Design Analysis L-002457, Revision 8, including Attachment 0), in a machine-readable format (e.g.,

text file, spreadsheet). Provide the raw meteorological data from Peoria and Springfield, Illinois, which were used in the analysis for the period of record at these stations.

b. Provide detailed dimensions and size of the UHS in digitized format. Also, provide a Shapefile with the UHS dimensions, if one was used in the computational fluid dynamics model. Provide an explanation of the Shapefile format if different from standard geographic information system protocols.

c. Provide the thermal load table used in the UHS analysis in machine-readable format.

M. Pacilio Should you have any questions, please contact me at 301-415-1380 or by email at blake. purnell@nrc. gov.

Sincerely, IRA/

Blake Purnell, Project Manager Plant Licensing 111-2 and Planning and Analysis Branch Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-373 and 50-37 4

Enclosure:

Request for Additional Information cc w/encl: Listserv DISTRIBUTION:

PUBLIC LPL3-2 R/F RidsAcrsAcnwMaiiCenter RidsNrrPMLaSalle RidsRgn3MaiiCenter RidsNrrLASRohrer RidsNrrDssStsb GPurciarello, NRR JKaizer, NRR RidsNrrDorllpl3-2 BPurnell KErwin, NRO ADAMS A ccess1on N o.: ML14287A478 *b>':L memo OFFICE LPLI3-2/PM /LPL3-2/LA SBPB/BC* LPL3-2/BC LPL3-2/PM NAME BPurnell SRohrer GCasto TTate BPurnell DATE 10/27/14 10/27/14 10/2/14 11/10/14 11/14/14 OFFICIAL OFFICE RECORD