ML20211P938

Informs NRC of Change to Commitment for MSRV Leakage Action Plan Only.Evaluation for Operability & Potential for Inadvertent Opening Will Be Made at Designated Points During Plan

ML20211P938
Person / Time
Site:	Limerick
Issue date:	10/15/1997
From:	Walter MacFarland PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20211P942	List: ML20211P938 ML20211P947
References
NUDOCS 9710220033
Download: ML20211P938 (2)

Text

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- &- gl - Wdtst o.MacFa hnd,IV, P.4.

s e President Umenck Generatng Station 3 v

, RECO NUCLEAR rem e- c-Po Box 2300 - . C

- A Uvr or PECO ENrucys Sanatoga. PA 19464 0920 61o 718 3000 rax 61o 718 3008 Pager 1800 672 2285 #8320 October 15,1997 Docket Nos. 50-352 50-353 License Nos. NPF-39 NPF 85 U.S. Nucl6ar Regulatory Commission

~ Attn: Document Control Desk Washington. DC 20555

- SUBJE7T: Limerick Generating Station. Units 1 and 2 -

Change to the Main Steam Safety Reliof Valve Leakage Action Plan !

By letters c'ated October 6,1995, and March 1,1996, PECO Energy committed to an action plan to address occurrences of Main Steam Safety Relief Valve (MSRV) leakage at Limerick Generating Station (LGS), Units 1 and 2. This commitment was a result of-an inadvertent MSRV opening event on September 11,1995, after degradation of the MSRV from prolonged pilot seat steam leakage. The purpose of this letter is to inform the NRC of a change to the commitment for MSRV leakage action plan only. The action plans in the above referenced letters conceming Emergency Core Cooling System (ECCS) pump suction strainer differential pressures and suppression pool cleanliness remain unchanged from previous correspondence with the NRC.

- The significant change to this action plan is to provide operability determinations based

- on evaluated leak rate rather than a specific tailpipe temperature, and accordingly, to raise the trigger temperature for these evaluations. The attachment to this letter

_ provides the revised action to be taken at certain monitoring points.- Evaluations for operability and for the potemial for inadvertent opening will be made at designated -

- points during this plan.

' Justification for this action plan revision is based on additional experience which PECO Energy has gained in correlating tailpipe temperatures up to 240 degrees F with leak rate. The leak rate vs. temperature varies for each MSRV since tailpipe thermocouple distances from the MSRVs range from approximately 3 feet to 11 feet on uninsulated tailpipe. Leakage correlation with tailpipe temperatures to date shows that a tailpipe temperature of 240 degrees F conesponds to a leak rate well below 100 lbm/hr for a!!

thermocouple configurations. The MSRVs were designed to ba tolerant to this leak rate. Data also shows that setpoint drift of +/1% is not a concem for a leak rate up to -

200 lbm/hr. This data also shows that the va:ues of leakags are generally very low at

- the initial evaluation temperature of 225 degrees F per the present action plan. The _g revised action plan provides an initial response to MSRV leakage at leakage values which are more appropriate to be concemed with MSRV setpoint operability. The i I revised action plan is based in part on the success of an MSRV pilot thermocouple modification which provides the ability to distinguish pilot leakage from main valve QV T

leakage.

Leak rates which result in Ygher renges of tailpipe temperatures, i.e., above 240 degrces F, are able to be determined using other plant parameters such as

- suppression poci temperature rise or mass input. Above 240 degrees F, the correlation precision of the leak rate value using tailpipe temperature is not as good and leakage

-9710220033 971010

-PDR ADOCK-05000 52

Docket Nos. 50-352 and 50-353 ,

October 15,19977 Page 2 precision of the leak rate value using tailpipe temperature is not as good and leakage monitoring will be done using a combination of pilot temperatures, tailpipe temperatures, suppression pool heatup, and suppression pool mass input. This action plan revision is based on evaluated MSRV leakage values instead of the previous 250 degree and 275 degree F action points. Tailpipe temperatures of 250 degrees F and -

275 degrees F correspond to a wide range of possible leahage rates depending on the linear placement of tailpipe thermocouples. Evaluations of the potential for inadvertent opening and the need for preemptive outage initiation will be made based on trending -

- of leakage well below the 1000 lbm/hr at which inadvertent opening could be possible.

Normal MSRV leakage degradation is a slow process, allowing the time needed to make those evaluations and to monitor leakage trends to conservatively determine the potential for inadvertent opening. Operability evaluations for setpoint drift and manual / remote actuation are also made above 240 degrees F when leakage exceeds the design leak tolerance of the MSRVs. - As always, these evaluations will be made

- based on the best available data when the leakage trend is behaving as previously experienced.

Larger than expected increases in leak rate require a more urgent assessment of the leakage mechanism and appro priate action will be taken if the leakage mechanism appears abnormal. For examp e, an abnormai leakage trend on the Unit 1 'J' MSRV resulted in a conservative management decision to shutdown Unit 1 during June of ,

1997. A gasket leak in the range of 30 lbm/hr, a relatively low leakage value, provided cause for cono3rn since its trend was higher than normally expected with a pilot valve seat leak, the ncimal cause of pilot valve leakage Present LGS experience is that a few MSRVs have pilot valve leaks over an operating cycle, and that an outage may or may not be required for this leakage. PECO Energy has made conservative decisions regarding MSRV leakage by taking advantage of unit shutdowns for other reasons to replace leaking MSRVs at very low leak rates in the interest of preventing less opportune shutdowns later in the operating cycle.

MSRV main valve leakage concems are primarily b. sed on the need for increased suppression pool cooling. An outage for MSRV replacement for main seat leakage will be conservatively taken before reaching 1000 lbm/hr, the same criteria for a pilot valve leak.

The application of the predictive techniques described in this letter represent a more accurate method of determining MSRV leakage characteristics. This provides PECO Energy better ability to continue to make conservative decisions to ensure the safe operation of LGS.

If you have any questions, please do not hesitate to contact us.

Very truly yours, 1 -

h) y& R Attachment

- cc: H. J. Milir, Administrator, Region I, USNRC w/ attachment

. A. L. Burritt, USNRC Senior Resident inspector, LGS "

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