RS-07-003, Additional Information Supporting Request for License Amendment to Increase Main Steam Safety Valve Lift Setpoint Tolerance and Standby Liquid Control System Enrichment

Additional Information Supporting Request for License Amendment to Increase Main Steam Safety Valve Lift Setpoint Tolerance and Standby Liquid Control System Enrichment

ML070110416
Person / Time
Site:	Dresden
Issue date:	01/11/2007
From:	Jury K Exelon Generation Co, Exelon Nuclear
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RS-07-003, TAC MD2166, TAC MD2167
Download: ML070110416 (4)

Text

Exelon ..

Exelon Generation wwwexeloncorp .com Nuclear 4300 Winfeld Road Warrenville, IL 60555 RS-07-003 January 11, 2007 U. S. Nuclear Regulatory Commission ATTN : Document Control Desk Washington, DC 20555-0001 Dresden Nuclear Power Station, Units 2 and 3 Renewed Facility Operating License Nos. DPR-19 and DPR-25 NRC Docket Nos . 50-237 and 50-249 Subject : Additional Information Supporting Request for License Amendment to Increase Main Steam Safety Valve Lift Setpoint Tolerance and Standby Liquid Control System Enrichment (TAC MD2166 and MD2167)

Reference : 1. Letter from P . R . Simpson (Exelon Generation Company, LLC) to U . S.

NRC, "Request for License Amendment to Increase Main Steam Safety Valve Lift Setpoint Tolerance and Standby Liquid Control System Enrichment," dated June 2, 2006 In Reference 1, Exelon Generation Company, LLC (EGC) requested an amendment to Renewed Facility Operating License Nos . DPR-19 and DPR-25 for Dresden Nuclear Power Station (DNPS), Units 2 and 3 . The proposed change revises Technical Specification Surveillance Requirement (SR) 3 .4.3 .1 to increase the allowable as-found main steam safety valve lift setpoint tolerance from +/- 1% to t 3%. In addition, the proposed change revises SR 3.1 .7.10 to increase the enrichment of sodium pentaborate used in the Standby Liquid Control System from >_ 30 .0 atom percent boron-10 to >_ 45.0 atom percent boron-10 .

The NRC has requested additional information to complete its review . In response, EGC is providing the attached information .

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 1 . The information provided in this submittal does not affect the bases for concluding that the proposed license amendment does not involve a significant hazards consideration.

January 11, 2007 U . S . Nuclear Regulatory Commission Page 2 There are no regulatory commitments contained in this letter. Should you have any questions concerning this letter, please contact Ms . Michelle Yun at (630) 657-2818 .

I declare under penalty of perjury that the foregoing is true and correct. Executed on the 11 'n day of January 2007.

Respectfully, Keith R. Jury Director - Licensing and Regulatory Affairs  : Response to NRC Request for Additional Information cc : NRC Senior Resident Inspector NRC Regional Administrator, Region III

ATTACHMENT 1 Response to NRC Request for Additional Information

ATTACHMENT 1 NRC Request Page 3 of 12 in Attachment 1 to the June 2, 2006 [for Dresden Nuclear Power Station],

submittal states that all nine MSSVs are required to be operable by TS 3.4.3, "Safety and Relief Valves," and that the function of all nine safety valves is required to be operable to satisfy the assumptions of the safety analysis . However, on Page 2-2 of GE-NE-0000-0053-8435-R1 P in Table 2-1, "Overpressure Results with 3% Setpoint Tolerance," it states that the number of dual safety relief valves (DSRVs) credited for Dresden Units 2 and 3 is zero, and the number of safety valves credited is eight. Based on the information in this table it appears that only eight safety valves were credited for the overpressure analyses at Dresden which is inconsistent with the information on Page 3 of 12 in Attachment 1 to the June 2, 2006, submittal. Please confirm whether the Dresden Unit 2 Cycle 20 and [Dresden] Unit 3 Cycle 19 reload analyses credited all nine safety valves .

Response

The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code requires the reactor pressure vessel be protected from overpressure during upset conditions by self-actuated safety valves . As part of the nuclear pressure relief system, the size and number of safety valves are selected such that the peak pressure in the nuclear system will not exceed the ASME Code limits for the reactor coolant pressure boundary . Each unit is designed with nine safety valves, one of which also functions in the relief mode. This valve is a dual function Target Rock safety/relief valve (S/RV) . The current reload analyses for Dresden Nuclear Power Station, Unit 2 Cycle 20 and Unit 3 Cycle 19 credit only eight of nine safety valves, with the S/RV not credited in the analysis . Adherence to technical specifications that require the safety function of nine safety valves to be operable supports reload analyses and provides additional conservatism and assurance of the safety function during an overpressure event .