ML041250014

E-Mail, Increasing No. S/Rv License Amendment Request

ML041250014
Person / Time
Site:	Dresden
Issue date:	02/03/2004
From:	Banerjee M NRC/NRR/DLPM/LPD3
To:	Exelon Corp
Banerjee M, NRR/ADPT, 415-2277
References
Download: ML041250014 (3)

Text

From: Maitri Banerjee To: ken.nicely@exeloncorp.com Date: 02/03/2004 3:49PM

Subject:

Re: Increasing No. S/RV license amendment request NRC review of the information provided by you resulted in the following questions from the reviewers. Please give me a call to set up a conference call to discuss with the reviewers if you need clarifications:

1. In the licensees response to last RAI #3, they stated out of 40 tests of main steam safety valves (including the safety/relief valves) over the past four outages on each unit, five valves exhibited drift resulting in an as-found setpoint greater than 1% higher than the TS setpoint.

The highest as found setpoint was 2.29% higher than the TS setpoint. The resulting as-found setpoint of 2.29% was recorded from Safety/Relief Valve 215 which was only tested once in 3 cycles. S/RV 215 is one of the valves in group 1 (Tag Pressure 1135) and a delay in it opening at the assumed setpoint can cause an even greater resulting peak pressure for the ASME overpressure analysis.

2. The licensee also makes the conclusion that given the history of the valve test results, there is reasonable confidence that the 1% valve tolerance assumed bounds actual valve performance, since only five valves out of 40 tests have exceeded the assumed setpoint in the ASME overpressure analysis, and since the majority of the setpoint drift is in the downward direction. Staff does not find that this conclusion holds up under preliminary statistical analysis.

In a preliminary statistical analysis performed by staff using the valve test results provided from the licensee, it is unclear as to how the licensee can say there is reasonable confidence that the assumed 1% valve tolerance bounds actual valve performance. The first question is what is "reasonable" confidence according to the licensee (i.e., 95/95, 95/90, 90/90, etc.)? Staffs preliminary statistical analyses show that the spread of data does not hold with confidence that

+1% is acceptable. Even with 90/90 percent confidence, staffs preliminary statistical analysis shows that the lowest setpoint tolerance acceptable is slightly above 1.5%.

3. The licensee also states that there are significant conservatisms in both the ASME and ATWS analyses that following an occurrence of as-found setpoint drift of the magnitudes experienced, an evaluation performed would show that analysis acceptance criteria would be met. The staff does not consider the assumptions made in the ASME overpressure analysis to be "conservatisms" but rather NRC approved methodologies to account for uncertainties. For example, the licensee assumes 102% power in the ASME overpressure analysis to account for power measurement uncertainty. Therefore, the staff does not find the licensee can conclude they have a "reasonable" confidence that the assumed 1% tolerance is bounding based on the uncertainties that are incorporated into the ASME overpressure analyses based on NRC approved methodologies.

4. Given the first three arguments, the staff suggests that the licensee reanalyze the ASME overpressure analysis assuming a higher tolerance for the lowest opening S/RV (1135 psig) to ensure that design criteria can still be met given the valve test data drift magnitudes previously experienced.

5. With reference to Dresden Unit 3 LER 2002-004-00, "Main Steam Safety Valves Failed the Technical Specification As-Found Lift Setpoint," dated December 13, 2002, one of the corrective actions in the LER stated

"Regulatory Assurance to submit a Technical Specification Amendment Request to the Nuclear Regulatory Commission to increase the Main Steam Safety Valve setpoint tolerance as reflected in the analyses performed." Please let us know of actions taken by Exelon to address this commitment. For example, was the ASME overpressure analysis revised to reflect the as-found tolerance of the lowest set pressure SRV?

CC: Charles Hammer; Tanya Ford; Zena Abdullahi

Mail Envelope Properties (40200967.8C7 : 8 : 21450)

Subject:

Re: Increasing No. S/RV license amendment request Creation Date: 02/03/2004 3:49PM From: Maitri Banerjee Created By: MXB@nrc.gov Recipients exeloncorp.com ken.nicely (ken.nicely@exeloncorp.com) nrc.gov owf2_po.OWFN_DO CGH CC (Charles Hammer)

TNF CC (Tanya Ford)

ZXA CC (Zena Abdullahi)

Post Office Route exeloncorp.com owf2_po.OWFN_DO nrc.gov Files Size Date & Time MESSAGE 4740 02/03/04 03:49PM Options Expiration Date: None Priority: Standard Reply Requested: No Return Notification: None Concealed

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