ML20012G535

Comments on Util 921215 Request for one-time Extension of LCO for DG in Order to Perform Preventive Maint.Suggests That Util Withdraw Request & Refrain from Practice of Discretionary Removal of DG for Preventive Maint

ML20012G535
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	03/01/1993
From:	Sendano R VERMONT, STATE OF
To:	Reid D VERMONT YANKEE NUCLEAR POWER CORP.
References
NUDOCS 9303090003
Download: ML20012G535 (2)

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_f STATE OF VERMONT DEPARTMENT OF PUBLIC SERVICE 120 STATE STREET MONTPELIER, VT 05620-2601 TEL: (802) 828-2811 FAX: (802) 828 2342

[O,27l TTY /TDD (VT): 1-800-734-8390 March 1, 1993 Donald Reid, Vice President &

Manager of Operations Vermont Yankee Nuclear Power Corp.

RD #5, Box 169 Brattleboro, VT 05301

Subject:

Discretionary Maintenance of Diesel Generators during Plant Operation

Dear Don:

In a December 15, 1992 letter to the Nuclear Regulatory Commission (NRC) , Vermont Yankee requested a one-time extension of its Limiting Condition for Operation (LCO) for diesel generators in order to perform preventive maintenance. In this letter, Vermont Yankee states:

"The proposed change would not involve a significant increase in the probability or consequences of an accident previously evaluated."

" Approval of this request involves an insignificant reduction in the margin of safety...."

This evaluation addresses the limited issue of a 7-day LCO extension. These same judgements regarding significance would apply to the broader practice of voluntarily removing the diesel generators from service for preventive maintenance within existing LCO limits.

Vermont Yankee Technical Specifications, through LCO's, allow safety-systems to be inoperable for periods of time before plant shutdown is required. It is apparent to us that inoperable safety systems reduce margins of safety. Since our litigation in 1988 in the area of alternate testing, we have been' expressing a desire for established bases for system out-of-service times.

What is the risk of removing diesel generators from service for 7-days? For 14-days? For multiple times during the year?

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In the Vermont Yankee evaluation, the use of terminology, "does not involve a significant increase" and " involves an insignificant reduction," shows imprecision and reliance upon judgement. However, techniques and methodologies exist to quantify both the risks and benefits of discretionary removal from service of safety-systems. All nuclear plants have been required by NRC to prepare Individual Plant Examinations (IPEs) assessing safety risks through probabilistic risk assessment methods. While some plants have made submittals, Vermont Yankee is not scheduled to submit the results of its IPE until December 1993. It is expected that the significance of removal from service of diesel generators can be assessed through this risk study.

Consequently, we make the following two requests of Vermont Yankee. Since the " significance" or " insignificance" of i discretionary removal from service of diesel generators is a matter of judgement and has not been quantified, we request that Vermont Yankee: .

1) Withdraw its December 15, 1992, request for technical {

specification amendment for a one-time extension of the ,

diesel generator LCO.

2) Refrain from the practice of discretionary removal from service of diesel generators for preventive maintenance I

until the significance of risk associated with the practice is assessed through a submitted IPE; and i If you have questions, regarding these requests, please  :

call.

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Richard P. S ano Commissioner cc: /D. Dorman, NRC Project Manager H. Eichenholz, NRC Senior Resident I

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