ML102160190

Request for Additional Information Related to License Amendment Regarding Ultimate Heak Sink

ML102160190
Person / Time
Site:	Byron
Issue date:	08/18/2010
From:	David M Plant Licensing Branch III
To:	Pardee C Exelon Nuclear
David Marshall NRR/DORL/LPL3-2 415-154
References
TAC ME1669, TAC ME1670
Download: ML102160190 (5)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555*0001 August 18, 2010 Mr. Charles G. Pardee President and Chief Nuclear Officer Exelon Nuclear 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

BYRON STATION, UNIT NOS. 1 AND 2 - REQUEST FOR ADDITIONAL INFORMATION RELATED TO LICENSE AMENDMENT REGARDING ULTIMATE HEAT SINK (TAC NOS. ME1669 AND ME1670)

Dear Mr. Pardee:

By letter to the Nuclear Regulatory Commission (NRC) dated June 30, 2009 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML091831253), as supplemented by letters dated January 25 and July 1, 2010 (ADAMS Accession Nos.

ML100280553 and ML101830041, respectively), Exelon Generation Company, LLC (the licensee), submitted a license amendment request to revise Technical Specification 3.7.9, "Ultimate Heat Sink (UHS)," to add additional essential service water (SX) cooling tower fan requirements as a function of SX pump discharge temperature to reflect the results of a revised analysis for the UHS.

The NRC staff is reviewing your submittals, and has determined that additional information is required to complete its review. The specific information requested is addressed in the enclosed Request for Additional Information (RAI). The RAI was discussed with your staff on August 18, 2010, and they agreed to respond within 60 days after the date of this letter.

The NRC staff considers that timely responses to requests for additional information help ensure sufficient time is available for staff review and contribute toward the NRC's goal of efficient and effective use of staff resources. If circumstances result in the need to revise the requested response date, please contact me at (301) 415-1547.

~~;/~()

M~;"II J. David, slla:r?Oject ~er Plant Licensing Branch 111-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. STN 50-454 and STN 50-455

Enclosure:

Request for Additional Information cc w/encls: Distribution via Listserv

REQUEST FOR ADDITIONAL INFORMATION BYRON STATION, UNIT NOS. 1 AND 2 DOCKET NOS. STN 50-454 AND STN 50-455 The Nuclear Regulatory Commission (NRC) staff is reviewing Exelon Generation Company, LLC's (the licensee's) license amendment request (LAR) dated June 30, 2009 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML091831253), as supplemented by letters dated January 25 and July 1, 2010 (ADAMS Accession Nos.

ML100280553 and ML101830041, respectively). The LAR requests to revise Technical Specification (TS) 3.7.9, "Ultimate Heat Sink (UHS)," to add additional essential service water (SX) cooling tower fan requirements as a function of SX pump discharge temperature to reflect the results of a revised analysis for the UHS.

The NRC staff has determined that the following additional information is required to complete its review.

1. The scenarios presented in your June 30, 2009, January 25, and July 1, 2010, submittals, which established the proposed revisions to TS 3.7.9 LCO, ACTIONS, and Surveillance Requirements (as stated in your January 25, 2010, submittal), assumed SX flow rates with the trains of each unit being cross connected and the opposite unit crosstie valves closed.

Two SX pumps are running in the accident unit and one SX pump is running in the non accident unit.

However, the updated final safety analysis report (UFSAR) currently states that the redundant SX loops can be operated as two separate loops in each unit, and TS Bases B 3.7.8 has provision to cross tie each unit's trains and also cross-tie the units as stated below:

UFSAR Section 9.2.1.2, Essential Service Water System, states that the essential service water system is divided into two redundant loops for each unit. The system may be operated with the loops cross-tied or as two separate loops.

TS Bases B 3.7.8 states that the SX system includes provisions to crosstie the trains (unit-specific crosstie), as well as provisions to crosstie the units (opposite-unit crosstie). The opposite-unit crosstie valves (1SX005 and 2SX005) must both be open to accomplish the opposite-unit crosstie. The system is normally aligned with the unit-specific crosstie valves open and the opposite-unit crosstie valves closed.

a. Are the proposed revisions to TS 3.7.9 (LCO, ACTIONS and Surveillance Requirements) satisfactory for keeping basin temperature below 100°F when the SX system is aligned as two separate loops in one or both units? Are the proposed revisions to TS 3.7.9 satisfactory for maintaining basin temperature below 100°F when the SX system is aligned with the unit crosstie valves open? Please explain. If not, what course of action should be implemented such that the proposed revisions to TS 3.7.9 ensure the basin temperature will not exceed 100°F for all SX system operating alignments?

ENCLOSURE

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b. Do any procedures, UFSAR sections, or TS Bases need revision to ensure that the proposed revisions to TS 3.7.9 are satisfactory for all system operating alignments and modes of operation in your UFSAR and TS Bases? Please explain.

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c. If the trains were operating as two separate loops as stated in UFSAR Section 9.2.1.2, discuss the validity of the proposed revision to TS 3.7.9 when the assumed single failure is a loss of an emergency diesel generator (EDG). Loss of an EDG could result in each unit's single SX pump (after a loss-of-coolant accident (LOCA)) drawing from the same tower with less than four fans running in that tower (depending on which fans are out of service). If this lineup is valid, discuss how the calculation would account for stratification or uneven mixing in the basin.

2. Assumption 3.4 of Appendix H of calculation M-MSD-009 (attachment 4 of the June 30, 2009 submittal), states that half of the reactor containment fan cooler (RCFC) heat load on the accident unit is shed at or prior to 30 minutes. Section 8 of Appendix H states, "Results are valid only if half of the RCFC heat load on the accident unit is shed at, or prior to, 30 minutes.

Procedures would have to be changed to implement this operator action."

Shedding the heat load from two of the four RCFCs would cause higher steam/air temperatures in containment for the remaining two operating RCFCs and thus increase their heat removal rate. Therefore, reducing the heat load contribution of the RCFCs by half seems to be a liberal assumption, especially since the same amount of energy has to be removed from containment whether two or four RCFCs are in operation after a LOCA.

Securing two of the four RCFCs would seem to make the peak basin temperature occur later and higher than assuming that the half the heat input from containment to the basin was eliminated. As shown in the June 30, 2009, submittal (page 6 of 11), 4 of the 5 scenarios that establish the proposed TS 3.7.9 ACTIONS have a peak basin temperature above 99.5°F.

Please justify assumption 3.4 in light of the fact that the calculated maximum basin temperatures already peak very close to 100°F.

3. The proposed revisions to TS 3.7.9, when basin temperatures are above 80°F and fans are running in high speed, bound the current TS 3.7.9, whose basis considered the loss of an EDG as a single failure. Since scenarios 8C1 and 8D1 present new TS, the loss of an EDG might not be bounded by scenario 8C1 and/or scenario 8D1 (above 80°F). Scenarios 8C1 and 8D1 each have a loss of 2 cooling tower fans and half the RCFC heat load. The loss of an EDG also results in loss of 2 cooling tower fans and half the RCFC heat load, as well as the loss of an SX pump in the accident unit.

a. Verify that the proposed revisions to TS 3.7.9 determined by scenarios 8C1 and 8D1 keep basin temperature below 100°F if the single failure after a LOCA is a loss of an EDG. Please explain.

1. Assumes two separate loops means the returns to the cooling towers are also separate by closing valve 1SXQ11.

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b. Review and discuss other single failures that need to be considered, if any, for the proposed revisions to TS 3.7.9, which were based on scenarios 8C1 and 8D1.

4. Using the heat load given by the licensee in calculation M-MSD-009, the NRC staff performed an independent analysis and found a basin peak temperature above 100°F for scenarios 8C and 8D at approximately 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> after a LOCA. The heat load used by the NRC staff, being the same as in M-MSD-009, is half the actual containment heat load as noted in question 2, above.

What peak basin temperature does the licensee calculate for scenarios 8C and 8D (during cool down of the non-accident unit)? If basin temperature would exceed 100°F. what course of action is necessary to prevent basin temperature from exceeding 100°F for a LOCA and non-accident unit cool down?

ML100280553 and ML101830041, respectively), Exelon Generation Company, LLC (the licensee), submitted a license amendment request to revise Technical Specification 3.7.9, "Ultimate Heat Sink (UHS)," to add additional essential service water (SX) cooling tower fan requirements as a function of SX pump discharge temperature to reflect the results of a revised analysis for the UHS.

The NRC staff is reviewing your submittals, and has determined that additional information is required to complete its review. The specific information requested is addressed in the enclosed Request for Additional Information (RAI). The RAJ was discussed with your staff on August 18, 2010, and they agreed to respond within 60 days after the date of this letter.

The NRC staff considers that timely responses to requests for additional information help ensure sufficient time is available for staff review and contribute toward the NRC's goal of efficient and effective use of staff resources. If circumstances result in the need to revise the requested response date, please contact me at (301) 415-1547.

Sincerely, IRA!

Marshall J. David, Senior Project Manager Plant Licensing Branch 111-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. STN 50-454 and STN 50-455

Enclosure:

Request for Additional Information cc w/encls: Distribution via Listserv DISTRIBUTION:

PUBLIC RidsAcrsAcnw_MailCTR Resource RidsOgcRp Resource LPL3-2 RlF RidsRgn3MailCenter Resource GPurciarello, NRR RidsNrrDorlLpl3-2 Resource RidsNrrDssSbpb Resource GLapinsky. NRR RidsNrrLATHarris Resource RidsNrrDirslhpb Resource SRay, NRR RidsNrrPMByron Resource RidsNrrDirsltsb Resource MHamm, NRR RidsNrrDoriDpr Resource RidsNrrDeEeeb Resource NMilier. NRR ADAMS Accession No' .. ML102160190

• RAI E-mail Date NRR-088 OFFICE LPL3-2/PM LPL3-2/LA DSS/SBPB/BC LPL3-2/BC NAME MDavid THarris GCasto' RCarlson DATE 8/18/2010 8/5/2010 8/3/2009 8/18/2010