RS-13-051, Additional Information Supporting License Amendment Request to Revise Technical Specification 3.7.3, Ultimate Heat Sink

Additional Information Supporting License Amendment Request to Revise Technical Specification 3.7.3, Ultimate Heat Sink

ML13042A405
Person / Time
Site:	LaSalle   (NPF-011, NPF-018)
Issue date:	02/11/2013
From:	Gullott D Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RS-13-051, TAC ME9076, TAC ME9077
Download: ML13042A405 (10)

Text

4300 W!nfeld Road Warrenvllle, L 60555 630 657 2000 Office Exeton Generation, RS-13-051 10 CFR 50.90 February 11, 2013 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-001 LaSalle County Station, Units 1 and 2 Facility Operating License Nos. NPF-1 1 and NPF-18 NRC Docket Nos. 50-373 and 50-374

Subject:

Additional Information Supporting License Amendment Request to Revise Technical Specification 3.7.3, "Ultimate Heat Sink"

References:

1)

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

dated July 12, 2012 2)

Letter from D. M. Gullott (Exelon Generation Company, LLC) to U. S. Nuclear Regulatory Commission, "Supplemental Information Related to License Amendment Request to LaSalle County Station, Units 1 and 2 Technical Specification 3.7.3, 'Ultimate Heat Sink,"' dated September 17, 2012 3)

Letter from N. J. DiFrancesco (U. S. Nuclear Regulatory Commission) to M. J. Pacilio (Exelon Generation Company, LLC), "LaSalle County Station, Units 1 and 2 - Request for Additional Information Related to License Amendment Request to Technical Specification 3.7.3 Ultimate Heat Sink (TAC Nos. ME9076 and ME9077)," dated January 9, 2013 4)

Letter from P. R. Simpson (Exelon Generation Company, LLC) to U. S. Nuclear Regulatory Commission, "Response to Request for Additional Information Related to License Amendment Request to Technical Specification 3.7.3,

'Ultimate Heat Sink,"' dated January 18, 2013 In Reference 1, Exelon Generation Company, LLC, (EGC) requested an amendment to the Technical Specifications (TS) of Facility Operating License Nos. NPF-1 1 and NPF-18 for LaSalle County Station, Units 1 and 2 (LSCS). The license amendment would allow the TS temperature limit of the cooling water supplied to the plant from the Ultimate Heat Sink (UHS) to vary with the observed diurnal cycle. EGC supplemented Reference 1 with a letter dated September 17, 2012 (Reference 2).

1 4300 Winfield Road W3rrenville, !L 60555 Exelon Generation 630 657 2000 Office RS-13-051 10 CFR 50.90 February 11, 2013 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-001 LaSalle County Station, Units 1 and 2 Facility Operating License Nos. NPF-11 and NPF-18 NRC Docket Nos. 50-373 and 50-374

Subject:

Additional Information Supporting License Amendment Request to Revise Technical Specification 3.7.3, "Ultimate Heat Sink"

References:

1) Letter from D. M. Gullott (Exelon Generation Company, LLC) to u. S. Nuclear Regulatory Commission, "Request for a License Amendment to LaSalle County Station, Units 1 and 2, Technical Specification 3.7.3, 'Ultimate Heat Sink,'11 dated July 12,2012

2) Letter from D. M. Gullott (Exelon Generation Company, LLC) to u. S. Nuclear Regulatory Commission, "Supplemental Information Related to License Amendment Request to LaSalle County Station, Units 1 and 2 Technical Specification 3.7.3, 'Ultimate Heat Sink,'" dated September 17,2012

3) Letter from N. J. DiFrancesco (U. S. Nuclear Regulatory Commission) to M. J. Pacilio (Exelon Generation Company, LLC), "LaSalle County Station, Units 1 and 2 - Request for Additional Information Related to License Amendment Request to Technical Specification 3.7.3 Ultimate Heat Sink (TAC Nos. ME9076 and ME9077)," dated January 9,2013

4) Letter from P. R. Simpson (Exelon Generation Company, LLC) to u. S. Nuclear Regulatory Commission, "Response to Request for Additional Information Related to License Amendment Request to Technical Specification 3.7.3,

'Ultimate Heat Sink,'" dated January 18, 2013 In Reference 1, Exelon Generation Company, LLC, (EGC) requested an amendment to the Technical Specifications (TS) of Facility Operating License Nos. NPF-11 and NPF-18 for LaSalle County Station, Units 1 and 2 (LSCS). The license amendment would allow the TS temperature limit of the cooling water supplied to the plant from the Ultimate Heat Sink (UHS) to vary with the observed diurnal cycle. EGC supplemented Reference 1 with a letter dated September 17, 2012 (Reference 2).

February 11, 2013 U. S. Nuclear Regulatory Commission Page 2 In Reference 3, the U. S. Nuclear Regulatory Commission (NRC) requested additional information to complete its review of the proposed license amendment request. Attachments 1, 2 and 3 of Reference 4 provided the requested information, with the exception of Questions 3 and 5 of Reference 3. As discussed with the NRC on January 17, 2013 and documented in Reference 4, those responses would be provided in a separate submittal.

The Attachment of this submittal provides the requested information for Questions 3 and 5 of Reference 3.

EGC has reviewed the information supporting a finding of no significant hazards consideration that was previously provided to the NRC in Attachment 1 of Reference 2. The additional information provided in this submittal does not affect the bases for concluding that the proposed license amendments do not involve a significant hazards consideration.

In accordance with 10 CFR 50.91, "Notice for public comment; State consultation," paragraph (b),

a copy of this letter and its attachments are being provided to the designated State of Illinois official.

There are no regulatory commitments contained in this submittal.

Should you have any questions concerning this letter, please contact Ms. Lisa A. Simpson at (630) 657-2815.

I declare under penalty of perjury that the foregoing is true and correct. Executed on the 11th day of February 2013.

Respectfully, David M. Gullott Manager - Licensing Exelon Generation Company, LLC

Attachment:

Additional Information Supporting License Amendment Request to Revise Technical Specification 3.7.3, "Ultimate Heat Sink" cc:

Illinois Emergency Management Agency - Division of Nuclear Safety February 11, 2013 U. S. Nuclear Regulatory Commission Page 2 In Reference 3, the U. S. Nuclear Regulatory Commission (NRC) requested additional information to complete its review of the proposed license amendment request. Attachments 1, 2 and 3 of Reference 4 provided the requested information, with the exception of Questions 3 and 5 of Reference 3. As discussed with the NRC on January 17, 2013 and documented in Reference 4, those responses would be provided in a separate submittal.

The Attachment of this submittal provides the requested information for Questions 3 and 5 of Reference 3.

EGC has reviewed the information supporting a finding of no significant hazards consideration that was previously provided to the NRC in Attachment 1 of Reference 2. The additional information provided in this submittal does not affect the bases for concluding that the proposed license amendments do not involve a significant hazards consideration.

In accordance with 10 CFR 50.91, IINotice for public comment; State consultation,1I paragraph (b),

a copy of this letter and its attachments are being provided to the designated State of Illinois official.

There are no regulatory commitments contained in this submittal.

Should you have any questions concerning this letter, please contact Ms. Lisa A. Simpson at (630) 657-2815.

I declare under penalty of perjury that the foregoing is true and correct. Executed on the 11 th day of February 2013.

Respectfully, David M. Gullott Manager - Licensing Exelon Generation Company, LLC

Attachment:

Additional Information Supporting License Amendment Request to Revise Technical Specification 3.7.3, IIUltimate Heat Sinkll cc:

Illinois Emergency Management Agency - Division of Nuclear Safety

ATTACHMENT Additional Information Supporting License Amendment Request to Revise Technical Specification 3.7.3, "Ultimate Heat Sink" In a letter dated January 9, 2013, the NRC requested that EGC provide additional information related to the LaSalle County Station (LSCS) proposed license amendment request submitted July 12, 2012. This Attachment provides the requested information for Questions 3 and 5 of the January 9, 2013, letter.

NRC Question 3:

Review of Weather Screening

Background:

The purpose of the LakeT-PC model analysis is to ensure that the temperature of the UHS during the design basis event will not result in the UHS exceeding the design limit for the cooling water supplied to the plant safety systems. Attachment 1 to the proposed license amendment request (LAR) states that the transit time of the plant accident energy through the UHS is approximately 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />. Section 4.0 of the proposed LAR describes the selection of the worst-case meteorological conditions for 1-day and 30-day periods.

Request: Justify the selection and use of a 24-hour worst-case meteorological period when analyzing a 30-hour transit time.

EGC Response to Question 3:

As documented in Reference 1 and in the LSCS UFSAR, LSCS is committed to Regulatory Guide (RG) 1.27, Revision 1. Section C.1.b of the Regulatory Guide states, in part, "Analysis of the temperature problem should use the worst 1-day and worst 30-day periods of meteorological record in the region resulting in minimum heat transfer to the atmosphere and maximum plant intake temperature." LSCS's UHS analysis is consistent with this regulatory guidance.

Although not committed to RG 1.27, Revision 2, LSCS performed a sensitivity evaluation consistent with the regulatory guidance in section B, which states, in part, "Alternatively, the worst 36-consecutive-day period from historical climatological data may be used as the design basis. This period may or may not include the worst 5-day, 1-day, or 30-day period."

Consistent with this guidance and the LSCS 30-hour UHS transit time, the worst 774 consecutive hours (30 hour3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> + 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> + 30 days) was used to evaluate the response of the UHS during the design event. The worst 774-hour period was determined by the screening process described in Reference 4 for the historical environmental period that created the highest running average UHS temperature for 774 continuous hours. Note this screening did not consider the transit time in selecting the worst 774-hour period, but used the period that created the highest running temperature average for 774 continuous hours. This evaluation demonstrated Figure 3 of Reference 1 remains limiting (i.e., the limiting temperature at 06:00 would be more than 3.5°F greater than the Reference 1 limit of 101.25°F).

Additionally, LSCS has completed a sensitivity evaluation of the UHS response considering the effects of the accident energy transit time though the UHS. This evaluation is further described in the response to Question 5.

Page 1 of 8 ATTACHMENT Additional Information Supporting License Amendment Request to Revise Technical Specification 3.7.3, "Ultimate Heat Sink" In a letter dated January 9,2013, the NRC requested that EGG provide additional information related to the LaSalle County Station (LSGS) proposed license amendment request submitted July 12, 2012. This Attachment provides the requested information for Questions 3 and 5 of the January 9, 2013, letter.

NRC Question 3:

Review of Weather Screening

Background:

The purpose of the LakeT-PC model analysis is to ensure that the temperature of the UHS during the design basis event will not result in the UHS exceeding the design limit for the cooling water supplied to the plant safety systems. Attachment 1 to the proposed license amendment request (LAR) states that the transit time of the plant accident energy through the UHS is approximately 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />. Section 4.0 of the proposed LAR describes the selection of the worst-case meteorological conditions for 1-day and 3~-day periods.

Request: Justify the selection and use of a 24-hour worst-case meteorological period when analyzing a 30-hour transit time.

EGC Response to Question 3:

As documented in Reference 1 and in the LSCS UFSAR, LSCS is committed to Regulatory Guide (RG) 1.27, Revision 1. Section C.1.b of the Regulatory Guide states, in part, "Analysis of the temperature problem should use the worst 1-day and worst 30-day periods of meteorological record in the region resulting in minimum heat transfer to the atmosphere and maximum plant intake temperature. II LSCS*s UHS analysiS is consistent with this regulatory guidance.

Although not committed to RG 1.27, Revision 2, LSCS performed a sensitivity evaluation consistent with the regulatory guidance in section B, which states, in part, "Alternatively, the worst 36-consecutive-day period from historical climatological data may be used as the design basis. This period mayor may not include the worst 5-day, 1-day, or 30-day period. II Consistent with this guidance and the LSGS 30-hour UHS transit time, the worst 774 consecutive hours (30 hour3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> + 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> + 30 days) was used to evaluate the response of the UHS during the design event. The worst 774-hour period was determined by the screening process described in Reference 4 for the historical environmental period that created the highest running average UHS temperature for 774 continuous hours. Note this screening did not consider the transit time in selecting the worst 774-hour period, but used the period that created the highest running temperature average for 774 continuous hours. This evaluation demonstrated Figure 3 of Reference 1 remains limiting (Le., the limiting temperature at 06:00 would be more than 3.5°F greater than the Reference 1 limit of 101.25°F).

Additionally, LSGS has completed a sensitivity evaluation of the UHS response considering the effects of the accident energy transit time though the UHS. This evaluation is further described in the response to Question 5.

Page 1 of 8

ATTACHMENT Additional Information Supporting License Amendment Request to Revise Technical Specification 3.7.3, "Ultimate Heat Sink" NRC Question 5:

Review of UHS Transient Heatup

Background:

The licensee has stated that the transit time for core standby cooling system (CSCS) flow across the UHS pond during a design-basis accident loss-of-coolant accident (DBA-LOCA) is 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> with the UHS sediment level of 1.5 feet. In the DBA-LOCA analysis, the licensee considered the worst 24-hour period of meteorological conditions for controlling parameters in determining peak UHS temperature. By considering the worst 24-hour period, the licensee's analysis showed that the peak temperature of the UHS after a LOCA, which started at 6:00 a.m., would be approximately 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> after the LOCA, which occurs 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> before any of the UHS water that is affected by accident heat input enters the plant intake.

Attachments I [Figure 17.7] and L [Appendix L9.4] of Calculation L-002457, "LaSalle County Station Ultimate Heat Sink Analysis," show the effects of the heat added to the UHS by the DBA-LOCA, whose effects do not reach the UHS outlet to the plant until 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> after the DBA-LOCA. Figure 17.7 shows temperatures near 140 OF initially entering the UHS immediately after the DBA and shows the UHS inlet temperature to be well above 120 OF for most of the first day after the DBA-LOCA, yet, the UHS outlet to the plant has already peaked at 107 OF at about 3:00 p.m. on the first day. According to Figure 4 of the LAR, the maximum temperature of the UHS outlet temperature on the second day is below the maximum temperature on the first day, indicating that the heat added by the DBA-LOCA has little effect on the UHS outlet temperature.

The seeming lack of influence upon peak UHS temperature by the accident heat and the meteorological conditions of second day after the accident could be attributed to a relatively cool, cloudy, or windy day after the first day following the DBA-LOCA, which is the first day of the 30-day critical period.

Issues: Heat waves where weather extremes have persisted for multiple consecutive days are not uncommon. Considering that a heat wave is in progress and the first critical time period of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> as used by the licensee, the first day of the worst 30-day period may not be representative of the actual second day after an accident. Also, in a letter dated May 6, 2011, the licensee stated that high temperatures and humidity during the daytime, in conjunction with minimal cooling at night and little precipitation during the summer months, results in elevated water temperatures in the LSCS UHS.

The NRC staff is not certain that the licensee has chosen appropriate critical time periods unique to the specific design of the CSCS pond. According to Regulatory Position 1 of Regulatory Guide (RG) 1.27, "the meteorological conditions resulting in minimum water cooling should be the worst combination of controlling parameters, including diurnal variations where appropriate, for the critical time period(s) unique to the specific design of the sink," and "sufficient conservatism should be provided to ensure that a 30-day cooling supply is available and that design basis temperatures of safety related equipment are not exceeded." In RG 1.27 it also states that "meteorological conditions considered in the design of the UHS should be selected with respect to the controlling parameters (i.e., wind speed, humidity, dew point, air temperature, solar radiation, etc.)."

The licensee selected a first critical time period of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, independent of the time of the accident and the UHS transit time. However, the NRC staff believes that the first critical time period would be 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> or greater, dependent upon time of accident initiation and UHS transit Page 2 of 8 ATTACHMENT Additional Information Supporting License Amendment Request to Revise Technical Specification 3.7.3, "Ultimate Heat Sink" NRC Question 5:

Review of UHS Transient Heatup

Background:

The licensee has stated that the transit time for core standby cooling system (CSCS) flow across the UHS pond during a design-basis accident loss-of-coolant accident (DBA-LOCA) is 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> with the UHS sediment level of 1.5 feet. In the DBA-LOCA analysis, the licensee considered the worst 24-hour period of meteorological conditions for controlling parameters in determining peak UHS temperature. By considering the worst 24-hour period, the licensee's analysis showed that the peak temperature of the UHS after a LOCA, which started at 6:00 a.m., would be approximately 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> after the LOCA, which occurs 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> before any of the UHS water that is affected by accident heat input enters the plant intake.

Attachments I [Figure 17.7] and L [Appendix L9.4] of Calculation L-002457, "LaSalle County Station Ultimate Heat Sink Analysis, II show the effects of the heat added to the UHS by the DBA-LOCA, whose effects do not reach the UHS outlet to the plant until 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> after the DBA-LOCA. Figure 17.7 shows temperatures near 140 of initially entering the UHS immediately after the DBA and shows the UHS inlet temperature to be well above 120 of for most of the first day after the DBA-LOCA, yet, the UHS outlet to the plant has already peaked at 107 of at about 3:00 p.m. on the first day. According to Figure 4 of the LAR, the maximum temperature of the UHS outlet temperature on the second day is below the maximum temperature on the first day, indicating that the heat added by the DBA-LOCA has little effect on the UHS outlet temperature.

The seeming lack of influence upon peak UHS temperature by the accident heat and the meteorological conditions of second day after the accident could be attributed to a relatively cool, cloudy, or windy day after the first day following the DBA-LOCA, which is the first day of the 30-day critical period.

Issues: Heat waves where weather extremes have persisted for multiple consecutive days are not uncommon. Considering that a heat wave is in progress and the first critical time period of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> as used by the licensee, the first day of the worst 30-day period may not be representative of the actual second day after an accident. Also, in a letter dated May 6,2011, the licensee stated that high temperatures and humidity during the daytime, in conjunction with minimal cooling at night and little precipitation during the summer months, results in elevated water temperatures in the LSCS UHS.

The NRC staff is not certain that the licensee has chosen appropriate critical time periods unique to the specific design of the CSCS pond. According to Regulatory Position 1 of Regulatory Guide (RG) 1.27, "the meteorological conditions resulting in minimum water cooling should be the worst combination of controlling parameters, including diurnal variations where appropriate, for the critical time period(s} unique to the specific design of the sink," and "sufficient conservatism should be provided to ensure that a 3~-day cooling supply is available and that design basis temperatures of safety related equipment are not exceeded." In RG 1.27 it also states that "meteorological conditions considered in the design of the UHS should be selected with respect to the controlling parameters (i.e., wind speed, humidity, dew point, air temperature, solar radiation, etc.}."

The licensee selected a first critical time period of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, independent of the time of the accident and the UHS transit time. However, the NRC staff believes that the first critical time period would be 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> or greater, dependent upon time of accident initiation and UHS transit Page 2 of 8

ATTACHMENT Additional Information Supporting License Amendment Request to Revise Technical Specification 3.7.3, "Ultimate Heat Sink" time. Using these variable and first critical time periods would yield more limiting and accurate results. The staff also believes that the first critical time period should be verified by assuming greater first critical time periods and performing the analysis and comparing results. The staff also believes that the analysis for each assumed accident start time, i.e., 6:00 a.m. - 9 a.m.,

etc., would have its own set of worst-weather data for its particular critical time period.

Request:

a.

The NRC staff requests that the licensee justify their selection of weather data and critical time periods or propose new analysis that would address the NRC staff concerns presented in Issues above.

EGC Response to Question 5a:

RG 1.27, Revision 1, Regulatory Position C.1.b states, in part, "Analysis of the temperature problem should use the worst 1-day and worst 30-day periods of meteorological record in the region resulting in minimum heat transfer to the atmosphere and maximum plant intake temperature... Applicants should be assured that either a normal or emergency shutdown during the worst 1-day and 30-day period of record will not result in plant intake water temperatures exceeding design basis temperatures." This was the basis for LSCS's selection of weather data.

In order to address the NRC's issues presented above, LSCS performed a sensitivity evaluation of the response of the UHS considering the accident energy transit time through the UHS. As described in Reference 1, the time required at the start of an accident for safety-related cooling water returned to the UHS from the plant to traverse the UHS and enter the plant intake is approximately 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

LSCS screened historical environmental data as described in Reference 2 for the 30-hour periods of time creating the highest running average UHS temperatures. These periods of time are then applied to the design event to determine the worst period (i.e., the period that creates the highest UHS temperature). For example, the period from June 22, 2009, to June 23, 2009, had the second highest running average for 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> for an accident starting at 0600 during the screening process. However, this time period generated the highest UHS temperature when applied to the design basis event. Therefore, the worst 30-hour environmental period was determined to exist from 0600 June 22, 2009, to 1200 June 23, 2009, for the 0600 event. The same screening process was performed for accidents starting at each three-hour increment in a 24-hour period. Additional screenings were performed for transit times (or first critical times) of 33, 36, and 39 hours4.513889e-4 days <br />0.0108 hours <br />6.448413e-5 weeks <br />1.48395e-5 months <br />. These additional screenings demonstrated the June 22, 2009, to June 23, 2009, period remained limiting for all considered accident starting times and transit times. A review of plant data revealed the environmental period from 0800 June 22, 2009, to 0200 June 24, 2009, resulted in the LSCS cooling lake increasing in temperature from 89 °F to 98°F. Consistent with the guidance of RG 1.27 Revision 2 (as described in the response to Question 3), the 774-consecutive-hour period starting with the worst 30-hour periods on June 22, 2009 were evaluated.

Excessive conservatism in the existing methodology was assessed and reduced for the sensitivity evaluation. The accident energy release profile to the UHS and the LAKET-PC Page 3 of 8 ATTACHMENT Additional Information Supporting License Amendment Request to Revise Technical Specification 3.7.3, "Ultimate Heat Sink" time. Using these variable and first critical time periods would yield more limiting and accurate results. The staff also believes that the first critical time period should be verified by assuming greater first critical time periods and performing the analysis and comparing results. The staff also believes that the analysis for each assumed accident start time, i.e., 6:00 a.m. - 9 a.m.,

etc., would have its own set of worst-weather data for its particular critical time period.

Request:

a. The NRC staff requests that the licensee justify their selection of weather data and critical time periods or propose new analysis that would address the NRC staff concerns presented in Issues above.

EGC Response to Question 5a:

RG 1.27, Revision 1, Regulatory Position C.1.b states, in part, "Analysis of the temperature problem should use the worst 1-day and worst 30-day periods of meteorological record in the region resulting in minimum heat transfer to the atmosphere and maximum plant intake temperature... Applicants should be assured that either a normal or emergency shutdown during the worst 1-day and 30-day period of record will not result in plant intake water temperatures exceeding design basis temperatures." This was the basis for LSCS's selection of weather data.

In order to address the NRC's issues presented above, LSCS performed a sensitivity evaluation of the response of the UHS considering the accident energy transit time through the UHS. As described in Reference 1, the time required at the start of an accident for safety-related cooling water returned to the UHS from the plant to traverse the UHS and enter the plant intake is approximately 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

LSCS screened historical environmental data as described in Reference 2 for the 30-hour periods of time creating the highest running average UHS temperatures. These periods of time are then applied to the design event to determine the worst period (Le., the period that creates the highest UHS temperature). For example, the period from June 22,2009, to June 23, 2009, had the second highest running average for 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> for an accident starting at 0600 during the screening process. However, this time period generated the highest UHS temperature when applied to the design basis event. Therefore, the worst 30-hour environmental period was determined to exist from 0600 June 22,2009, to 1200 June 23,2009, for the 0600 event. The same screening process was performed for accidents starting at each three-hour increment in a 24-hour period. Additional screenings were performed for transit times (or first critical times) of 33, 36, and 39 hours4.513889e-4 days <br />0.0108 hours <br />6.448413e-5 weeks <br />1.48395e-5 months <br />. These additional screenings demonstrated the June 22, 2009, to June 23, 2009, period remained limiting for all considered accident starting times and transit times. A review of plant data revealed the environmental period from 0800 June 22,2009, to 0200 June 24, 2009, resulted in the LSCS cooling lake increasing in temperature from 89°F to 98°F. Consistent with the guidance of RG 1.27 Revision 2 (as described in the response to Question 3), the 774-consecutive-hour period starting with the worst 30-hour periods on June 22, 2009 were evaluated.

Excessive conservatism in the existing methodology was assessed and reduced for the sensitivity evaluation. The accident energy release profile to the UHS and the LAKET-PC Page 3 of 8

ATTACHMENT Additional Information Supporting License Amendment Request to Revise Technical Specification 3.7.3, "Ultimate Heat Sink" wind function were both altered to reduce excessive conservatism. The accident energy release to the UHS in the existing design analysis follows the profile of the reactor core decay heat curve - exponentially decreasing function with time. The largest contributor to the accident energy is the reactor core decay heat from both units. Accident energy in addition to the decay heat transferred to the UHS is assumed to be added at a constant rate

- pump heat, area cooling heat, and sensible heat from the reactor pressure vessel and fuel (assumed constant for the first six hours of the event). This modeling results in the largest amount of accident energy being transferred to the UHS in the first hour and rapidly decreasing with time. This is considered to be excessively conservative. A realistic model of the accident energy transfer to the UHS would show the reactor core decay heat and sensible heat first being transferred to the suppression pool and then released to the UHS by operation of the RHR system. This results in a more steady accident energy transfer to the UHS as opposed to the exponential transfer of the existing design analysis.

The response to Question 2 of Reference 5 describes the LAKET-PC Hefner and Ryan wind functions application in the existing design analysis. When the calculated UHS temperature is within 2.5°F of the natural UHS temperature, the Lake-Hefner wind function is used in the evaporative and conductive/convective cooling terms. When the calculated UHS temperature is 2.5°F greater than the natural UHS temperature, the Ryan wind function is used. As described in the response to Question 2 of Reference 5 and NUREG-0693, this application of the Lake-Hefner wind function is conservative - decreases the amount of energy lost to the environment from the UHS water when the UHS temperature is within 2.5°F of the natural UHS temperature. Reference 3 describes the use of the Lake Hefner wind function for a natural water surface and use of the Ryan wind function for an artificially heated water surface. LSCS's UHS would be considered an artificially heated water surface at the beginning of the design event due to either the residual normal plant heat rejection to the UHS or the forced UHS initial temperature used in LAKET-PC.

Application of the Lake-Hefner wind function is not part of the NUREG-0693 described methodology. NUREG-0693 states, in part, "The formulation of the heat transfer formulae used has a number of built-in conservatisms, which tend to overestimate pond temperature.

One of the larger conservatisms is the choice of a wind dependence f(U). The Brady wind function employed seems to underestimate the evaporative flux, even when compared to Brady's own data. Brady's wind function is derived empirically from large lake data. A more accurate, but less conservative formula by Ryan on firmer physical grounds: (NUREG-0693 then presents the Ryan wind function used in the existing LAKET-PC design analysis). This formulae accounts for an expected increase in natural convection with increasing pond temperature, whereas Brady's wind function is not temperature dependent." The Lake-Hefner wind function used in LAKET-PC is similar to the Brady wind function, but even more conservative for low wind speeds as shown as follows:

Brady wind function: f(U) = 70 + 0.7U2 Lake-Hefner wind function: f(U) = 17U Where U = wind speed LAKET-PC input was altered to use only the Ryan wind function for critical periods of interest (approximately the first two days of the event) when performing the subject Page 4 of 8 ATTACHMENT Additional Information Supporting License Amendment Request to Revise Technical Specification 3.7.3, "Ultimate Heat Sink ll wind function were both altered to reduce excessive conservatism. The accident energy release to the UHS in the existing design analysis follows the profile of the reactor core decay heat curve - exponentially decreasing function with time. The largest contributor to the accident energy is the reactor core decay heat from both units. Accident energy in addition to the decay heat transferred to the UHS is assumed to be added at a constant rate

- pump heat, area cooling heat, and sensible heat from the reactor pressure vessel and fuel (assumed constant for the first six hours of the event). This modeling results in the largest amount of accident energy being transferred to the UHS in the first hour and rapidly decreasing with time. This is considered to be excessively conservative. A realistic model of the accident energy transfer to the UHS would show the reactor core decay heat and sensible heat first being transferred to the suppression pool and then released to the UHS by operation of the RHR system. This results in a more steady accident energy transfer to the UHS as opposed to the exponential transfer of the existing design analysis.

The response to Question 2 of Reference 5 describes the LAKET ~PC Hefner and Ryan wind functions application in the existing design analysis. When the calculated UHS temperature is within 2.5°F of the natural UHS temperature, the Lake*Hefner wind function is used in the evaporative and conductive/convective cooling terms. When the calculated UHS temperature is 2.5°F greater than the natural UHS temperature, the Ryan wind function is used. As described in the response to Question 2 of Reference 5 and NUREG*0693, this application of the Lake*Hefner wind function is conservative - decreases the amount of energy lost to the environment from the UHS water when the UHS temperature is within 2.5°F of the natural UHS temperature. Reference 3 describes the use of the Lake Hefner wind function for a natural water surface and use of the Ryan wind function for an artificially heated water surface. LSCS's UHS would be considered an artificially heated water surface at the beginning of the design event due to either the residual normal plant heat rejection to the UHS or the forced UHS initial temperature used in LAKET*PC.

Application of the Lake*Hefner wind function is not part of the NUREG*0693 described methodology. NUREG*0693 states, in part, liThe formulation of the heat transfer formulae used has a number of built*in conservatisms, which tend to overestimate pond temperature.

One of the larger conservatisms is the choice of a wind dependence f(U). The Brady wind function employed seems to underestimate the evaporative flux, even when compared to Brady's own data. Brady's wind function is derived empirically from large lake data. A more accurate, but less conservative formula by Ryan on firmer physical grounds: (NUREG~0693 then presents the Ryan wind function used in the existing LAKET-PC design analysis). This formulae accounts for an expected increase in natural convection with increasing pond temperature, whereas Brady's wind function is not temperature dependent.

1I The Lake-Hefner wind function used in LAKET-PC is similar to the Brady wind function, but even more conservative for low wind speeds as shown as follows:

Brady wind function: f(U) = 70 + 0.7U2 Lake-Hefner wind function: f(U) = 17U Where U = wind speed LAKET -PC input was altered to use only the Ryan wind function for critical periods of interest (approximately the first two days of the event) when performing the subject Page 4 of 8

ATTACHMENT Additional Information Supporting License Amendment Request to Revise Technical Specification 3.7.3, "Ultimate Heat Sink" sensitivity evaluations. This results in the evaporative and conductive/convective cooling terms remaining consistent with the methodology described in NUREG-0693.

The results of the sensitivity evaluation demonstrate LSCS's UHS design basis temperature of 107°F will not be exceeded when the worst environmental period is applied starting on June 22, 2009, and continuing for 774 hours0.00896 days <br />0.215 hours <br />0.00128 weeks <br />2.94507e-4 months <br />. The margin to the design temperature of 107°F with the initial UHS temperature at the proposed TS limiting temperature is shown in the following table:

Table 1 - UHS Temperature Response for 18" Sedimentation Time of Initial UHS Calculated Calculated Day Temperature 774-hour Margin (°F)

Design

(°F)

Post to UHS Basis (Proposed Design Design Event TS limit +

Event Temperature Occurs 0.75°F for Maximum of 107°F.

Instrument UHS Uncertainty)

Temp (OF) 00:00 104.53 104.53 2.47 03:00 102.72 104.96 2.04 06:00 102.00 105.39 1.61 09:00 103.19 105.69 1.31 12:00 104.75 105.05 1.95 15:00 104.75 104.75 2.25 18:00 104.75 104.75 2.25 21:00 104.75 104.75 2.25 24:00 104.53 104.53 2.47 Figures 1 and 2 show the response of the UHS for the design event occurring at 0600 for 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> (Figure 1) and for the continuous 774 hours0.00896 days <br />0.215 hours <br />0.00128 weeks <br />2.94507e-4 months <br /> (Figure 2).

Page 5 of 8 ATTACHMENT Additional Information Supporting License Amendment Request to Revise Technical Specification 3.7.3, IIUltimate Heat Sink ll sensitivity evaluations. This results in the evaporative and conductive/convective cooling terms remaining consistent with the methodology described in NUREG-0693.

The results of the sensitivity evaluation demonstrate LSCS's UHS design basis temperature of 107°F will not be exceeded when the worst environmental period is applied starting on June 22, 2009, and continuing for 774 hours0.00896 days <br />0.215 hours <br />0.00128 weeks <br />2.94507e-4 months <br />. The margin to the design temperature of 107°F with the initial UHS temperature at the proposed TS limiting temperature is shown in the following table:

Table 1 - UHS Temperature Response for 18 11 Sedimentation Time of Initial UHS Calculated Calculated Day Temperature 774-hour Margin (OF)

Design (OF)

Post to UHS Basis (Proposed Design Design Event TS limit +

Event Temperature Occurs 0.75°F for Maximum of 107°F.

Instrument UHS Uncertainty)

Temp (OF) 00:00 104.53 104.53 2.47 03:00 102.72 104.96 2.04 06:00 102.00 105.39 1.61 09:00 103.19 105.69 1.31 12:00 104.75 105.05 1.95 15:00 104.75 104.75 2.25 18:00 104.75 104.75 2.25 21:00 104.75 104.75 2.25 24:00 104.53 104.53 2.47 Figures 1 and 2 show the response of the UHS for the design event occurring at 0600 for 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> (Figure 1) and for the continuous 774 hours0.00896 days <br />0.215 hours <br />0.00128 weeks <br />2.94507e-4 months <br /> (Figure 2).

Page 5 of 8

ATTACHMENT Additional Information Supporting License Amendment Request to Revise Technical Specification 3.7.3, "Ultimate Heat Sink" Figure 1 - 48 Hour UHS Response 18" Sedimentation, 6 AM Start, New Heat Load, Ryan Wind Function 104 102 96 106 94 92 12:00 AM 12:00 PM 12:00 AM 6:00 AM Time 12:00 PM 12:00 AM 6:00 AM 6:00 PM 6:00 PM 6:00 AM Figure 2 - 774 Hour UHS Response 18" Sedimentation, 6AM Start, New Heat Load, Ryan Wind Function 0

10 15 Day 20 25 30 Page 6 of 8 ATTACHMENT Additional Information Supporting License Amendment Request to Revise Technical Specification 3.7.3, "Ultimate Heat Sink" Figure 1 - 48 Hour UHS Response 18" Sedimentation, 6 AM Start, New Heat Load, Ryan Wind Function 104+---------------------------------------------4-------~~----------_4 102+-----~~--~--------~~------------------_+------------~~------~

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12:00 AM 6:00AM 12:00 PM 6:00 PM 12:00 AM 6:00AM 12:00 PM 6:00 PM 12:00 AM 6;00 AM Time Figure 2 - 774 Hour UHS Response 18" Sedimentation, 6AM Start, New Heat Load, Ryan Wind Function 110 105 100 95 t 90 CD :; e 85 CD c.

E CD I-80 75 70 65 60 0

5 10 15 20 25 30 Day Page 6 of 8

ATTACHMENT Additional Information Supporting License Amendment Request to Revise Technical Specification 3.7.3, "Ultimate Heat Sink" These results demonstrate the UHS design temperature of 107°F will not be exceeded using the proposed TS limiting initial UHS temperatures of Attachment 1 Figure 3 of Reference 1.

The analytical modeling includes consideration of the combination of accident energy transit time through the UHS and the historical worst environmental period to create the maximum anticipated UHS temperature. The model also includes removal of excessively conservative characteristics of the existing design analysis described above (accident energy release and wind function application). Refer to Reference 1, Attachment 1, "Analysis Assumptions" for additional conservative assumptions that continue to exist in this sensitivity evaluation.

The worst 30-day evaporation weather period remains the same as determined in Reference 1. The sensitivity evaluation determined a negligible effect in inventory loss due to the changes in accident energy release and wind function application.

Request:

b.

Justify the constant transit time across the UHS pond that is used in your analysis, since reduction in UHS volume over the 30-day recovery period would cause transit time to decrease. If the decrease in transit time is modeled, justify whether the effective UHS volumes, surfaces, and transit times predicted in Attachment J remain applicable.

EGC Response to Question 5b:

The transit time of approximately 30.3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> given in Section 3.3 of L-002457 (Reference 4) refers to the initial transit time immediately following an accident. LAKET-PC takes into account the decrease in transit time due to the reduction in UHS volume. UHS transit time as taken from the output of Case 3a_6am of Reference 4 is presented in Figure 3 below.

Please note that LAKET-PC reports transit time in integer values only.

The total initial UHS volume and surface area are reduced due to the transient reduction in UHS volume inventory. The effective UHS volume and surface area are subsequently reduced by constant effective percentages determined in Attachment J of Reference 4.

Changes in UHS volume and surface area occur evenly over the entire UHS; therefore, the effective UHS volumes and surfaces percentages remain applicable.

Page 7 of 8 ATTACHMENT Additional Information Supporting License Amendment Request to Revise Technical Specification 3.7.3, "Ultimate Heat Sink" These results demonstrate the UHS design temperature of 107°F will not be exceeded using the proposed TS limiting initial UHS temperatures of Attachment 1 Figure 3 of Reference 1.

The analytical modeling includes consideration of the combination of accident energy transit time through the UHS and the historical worst environmental period to create the maximum anticipated UHS temperature. The model also includes removal of excessively conservative characteristics of the existing design analysis described above (accident energy release and wind function application). Refer to Reference 1, Attachment 1, "Analysis Assumptions ll for additional conservative assumptions that continue to exist in this sensitivity evaluation.

The worst 30*day evaporation weather period remains the same as determined in Reference 1. The sensitivity evaluation determined a negligible effect in inventory loss due to the changes in accident energy release and wind function application.

Request:

b. Justify the constant transit time across the UHS pond that is used in your analysis, since reduction in UHS volume over the 30-day recovery period would cause transit time to decrease. If the decrease in transit time is modeled, justify whether the effective UHS volumes, surfaces, and transit times predicted in Attachment J remain applicable.

EGC Response to Question 5b:

The transit time of approximately 30.3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> given in Section 3.3 of L-002457 (Reference 4) refers to the initial transit time immediately following an accident. LAKET -PC takes into account the decrease in transit time due to the reduction in UHS volume. UHS transit time as taken from the output of Case 3a_6am of Reference 4 is presented in Figure 3 below.

Please note that LAKET-PC reports transit time in integer values only.

The total initial UHS volume and surface area are reduced due to the transient reduction in UHS volume inventory. The effective UHS volume and surface area are subsequently reduced by constant effective percentages determined in Attachment J of Reference 4.

Changes in UHS volume and surface area occur evenly over the entire UHS; therefore, the effective UHS volumes and surfaces percentages remain applicable.

Page 7 of 8

ATTACHMENT Additional Information Supporting License Amendment Request to Revise Technical Specification 3.7.3, "Ultimate Heat Sink" Figure 3 - UHS Transit Time Following Accident 357 30 25 0

0 5

10 15 20 25 30 35 Pays Following Accident

References:

1)

Letter from D. M. Gullott (Exelon Generation Company, LLC) to U. S. Nuclear Regulatory Commission, "Request for a License Amendment to LaSalle County Station, Units 1 and 2, Technical Specification 3.7.3, 'Ultimate Heat Sink,"' dated July 12, 2012 2)

Letter from D. M. Gullott (Exelon Generation Company, LLC) to U. S. Nuclear Regulatory Commission, "Supplemental Information Related to License Amendment Request to LaSalle County Station, Units 1 and 2 Technical Specification 3.7.3, 'Ultimate Heat Sink,"' dated September 17, 2012 3)

MIT Report 161, "An Analytical and Experimental Study of Transient Cooling Pond Behavior," Ryan and Harleman, Massachusetts Institute of Technology, Cambridge Massachusetts, 1973 4)

Calculation L-002457, "LaSalle County Ultimate Heat Sink Analysis," Revision 7 5)

Letter from P. R. Simpson (Exelon Generation Company, LLC) to U. S. Nuclear Regulatory Commission, "Response to Request for Additional Information Related to License Amendment Request to Technical Specification 3.7.3, 'Ultimate Heat Sink,"'

dated January 18, 2013 Page 8 of 8 ATTACHMENT Additional Information Supporting License Amendment Request to Revise Technical Specification 3.7.3, IIUltimate Heat Sink ll Figure 3 - UHS Transit Time Following Accident 30~

__ ----------------------------------------------------~

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~

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O~------~------~------~------~------~------~------~

o 10 15 20 25 30 35 Days Following Accident

References:

1)

Letter from D. M. Gullott (Exelon Generation Company, LLC) to U. S. Nuclear Regulatory Commission, IIRequest for a License Amendment to LaSalle County Station, Units 1 and 2, Technical Specification 3.7.3, 'Ultimate Heat Sink,'11 dated July 12, 2012

2)

Letter from D. M. Gullatt (Exelon Generation Company, LLC) to u. S. Nuclear Regulatory Commission, "Supplemental Information Related to License Amendment Request to LaSalle County Station, Units 1 and 2 Technical Specification 3.7.3, 'Ultimate Heat Sink,1II dated September 17, 2012

3)

MIT Report 161, "An Analytical and Experimental Study of Transient Cooling Pond Behavior," Ryan and Harleman, Massachusetts Institute of Technology, Cambridge Massachusetts, 1973

4)

Calculation L-002457, "LaSalle County Ultimate Heat Sink Analysis," Revision 7

5)

Letter from P. R. Simpson (Exelon Generation Company, LLC) to u. S. Nuclear Regulatory Commission, "Response to Request for Additional Information Related to License Amendment Request to Technical Specification 3.7.3, 'Ultimate Heat Sink,"'

dated January 18, 2013 Page 8 of 8