ML103500317

Draft NRC RAI Byron Station, Units 1 and 2 - LAR Ultimate Heat Sink

ML103500317
Person / Time
Site:	Byron
Issue date:	12/16/2010
From:	Nicholas Difrancesco Plant Licensing Branch III
To:	Schofield L Exelon Corp
DiFrancesco N, NRR/DORL/LPL3-2, 415-1115
References
TAC ME1669, TAC ME1670
Download: ML103500317 (2)

Text

From: DiFrancesco, Nicholas Sent: Thursday, December 16, 2010 10:03 AM To: Lisa.Schofield@exeloncorp.com Cc: DiFrancesco, Nicholas; Wohl, Marilyn; 'jeff.hansen@exeloncorp.com'; Carlson, Robert

Subject:

Draft NRC RAI Re: Byron Station, Units 1 and 2 - LAR Re: Ultimate Heat Sink (TAC Nos. ME1669 and ME1670)

Ms. Lisa Schofield, By letter to the Nuclear Regulatory Commission (NRC) dated June 30, 2009, as supplemented by letters dated January 25, July 1, and November 8, 2010 (Agencywide Documents Access and Management System Accession Nos. ML091831253, ML100280553, ML101830041, and ML103120556, 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 Balance-of-Plant Branch has reviewed the information provided and determined that in order to complete its evaluation, additional information may be required. The draft RAI related to the staff review is provided below.

After reviewing the draft RAI, please contact me at 301-415-1115 to discuss the need for a teleconference concerning the RAIs and to discuss a due date for the response.

Respectfully, Nicholas DiFrancesco

Project Manager Nuclear Regulatory Commission Division of Operating Reactor Licensing nicholas.difrancesco@nrc.gov Tel: (301) 415-1115 Fax: (301) 415-1222 REQUEST FOR ADDITIONAL INFORMATION BYRON STATION, UNIT NOS. 1 AND 2 DOCKET NOS. STN 50-454 AND STN 50-455

1. General Design Criteria 44, "Cooling water," states, in part, that suitable redundancy in components and features shall be provided to assure the system safety function can be accomplished, assuming a single failure.

Generic Letter (GL) 80-30 states that Standard Technical Specification (STS) Limiting Conditions for Operation (LCO) were formulated to preserve the single failure criterion for systems relied upon in the safety analysis report. When the required redundancy is not maintained due to equipment failure, GL 80-30 provides for a temporary relaxation of the single failure criterion for specified conditions within an allowed outage time. When the single failure criterion is temporary relaxed for the allowed outage time, the system safety function can still be performed with the remaining components and features during the allowed outage time.

The licensee has apparently proposed a new Condition B where there would not be enough remaining components and features to accomplish the safety function during the allowed outage time [i.e. there would not be enough essential service water cooling tower (SXCT) fans to perform the safety function even without any additional single failure]. This is described as follows. In Response 1 c of Exelon Letter dated November 8, 2010, the licensee is proposing a new Condition B which would allow two required cooling tower fans to be inoperable for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> when the SX system is operating with SX trains on either unit split. This new Condition B could allow one fan to be inoperable in each SXCT. The licensee has cited GL 80-30 as justification for allowing two required cooling tower fans to be inoperable. But, four operable fans in an SXCT are required for the safety analysis when the SX trains are split. The licensee states this requirement in Response 1 C as follows, "Calculations indicated that with no SXCT fans out of service and the SX trains separated, the UHS temperature could be maintained at less than 100 F with four SXCT fans operating on the SXCT with flow."

With neither SXCT having four operable fans, neither SXCT would be able to perform the safety function during the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> allowed outage time. The staff requests the following:

a.) Justify allowing two required cooling tower fans to be inoperable when the SX is operating in the configuration of Table 3.7.9-2 or revise Condition B to meet regulatory requirements. b.) Explain how the operators are supposed to determine UHS operability when the SX trains are split on one unit and/or both units. (Attachment 3 of the June 30, 2009 submittal, "Markup of Proposed Technical Specifications Bases Pages" define operability of the UHS when each units SX system has crosstied SX trains. The TS Bases does not provide UHS operability criteria for split SX trains.) c.) Explain why and how often the SX trains are operated split for one and/or both units.

2. The up rate heat load for the scenarios presented in Exelon Letter dated November 8, 2010 for the scenarios where SX is split show a constant heat load to the UHS for approximately the first 19 minutes after a Loss-of-Coolant Accident. These heat loads differ from the heat loads in the scenarios presented in your June 30, 2009 submittal. The staff recognizes differences in heat loads to the UHS based on one train of SX in the November 8 submittal versus two trains of operating SX in your June 30, 2009 submittal.

a) Explain the reasons for differences in the heat load profiles of your June 30, 2009 submittal and your November 8, 2010 submittal. b) Explain why the heat load is constant in your November 8 submittal for the first 19 minutes, whereas the corresponding heat load for the first 19-20 minutes is not constant for the scenarios in the June 30, 2009 submittal.