ML20079G599

Provides Plans to Document Load Testing of Safeguards Diesel Generators for Current 18-month Surveillance Test Requirement,Per Generic Ltr 88-15

ML20079G599
Person / Time
Site:	Prairie Island
Issue date:	10/02/1991
From:	Parker T NORTHERN STATES POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-88-15, NUDOCS 9110090186
Download: ML20079G599 (2)

Text

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i40rthem States Power Company 414 Nicolle,1 Mall Minneapolis, Minnesota $54011927 i Telephone (612) 33@5W0 1 l

October 2, 1991 Technical Specification TS 4.6.A.3.c.

U S Nuclear Regulatory Conunission Attn: Docu:nent Control Desk Washington, DC 20555 PRAIRIE ISIAND NUCLEAR GENERATING PIANT Docket Nos. 50 282 1.icense Nos. DPR 42 50 306 DPF-60 i

Diesel Centrator Load Testine. Surveillance l

This letter provides our plans to document the load testing of our safeguards diesel generators for the current 18 month surveillance test requirement.

These plans were discussed with the Prairie Island Ptoject Manager, Armando Masciantonio, and it was agteed that we document the plans through this letter.

Backcround Generic Letter 88-15 dated September 11, 1988 entitled " Electric Power Systems - Inadequate Control over Design Processes" addresses the problem of diesel generator loading in excess of design rating. It discusses a situation where a plant's diesel generator technical specifications required testing at least once every 18 months for 60 minutes at a load equal to or greater than 3000 kw. However, the manufacturer required that the diesel be subjected to a special maintenance inspection to verify that the diesel has not been damaged if the time of operation between 3000 and 3300 kw exceeds 30 minutes. The concern is that testing beyond the inanufacturer's design limit could jeopardize the diesel generator capacity to reliably perform its intended safety function during an event in which loss of of fsite power occurs.

Prairie Island's safeguards diesel generators have a 30 minute rating between

-3000 and 3250 kw. The current Technical Specifications (Technical Specification 4.6.A,3.c.) require that each diesel generator operate once each 18 months for at least one hour while loaded to 3000 kw. This creates a situation where a diesel generator could easily be opera.t ed above the 3000 kw level inadvertently. Even a slightly miscalibrated instrument could put the nachine into the region f or a long enough duration to jeopardize confidence in its ability to perform its intended cafety function.

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e Nodhom States Power Company NR October 2, 1991 Page 2 Therefore, it is prudent to test the machine at lower level, thereby avoidin e soproaching too close to the 30 minute cing. The Technical Specification specifies 3000 kw with no tolerance given. Since it is nec possible to maintain a constant 3000 kw load with the equipment configuration of our diesel generator sets, we have to maintain the load within a band around the target load. For the current 18 month test interval, we have chosan-to test the machine-by setting the controller to maintain the load in a band below 3000 kw in order to avoid exceeding 3000 kw for any appreciable period of time. Ve have chosen 2910 kw as the low and of the targeted band

-because 2910 kw is greater than the design basis load. We expect the machine ,

to briefly drift below 2910 kw and above 3000 kw .iuring the duration of the load test but not long enough to invalidate the t nor to require a-special maintenance inspection.

By the time that the next Technical Specification required performance of this test is dee, we plan to have added two additional safeguards diesel generators "

- which vill decrease the design basis loading on the original diesel generators. We will then submit a License Amendment Request to it wer the test load value from 3000 kw to a reduced load with a tolerance. The lower end of the new test load requirements will exceed the design basis load with an appropriate margin and the upper end will be less than the 3000 kw 30 minute rating.

Please contact us if you require additional it. formation.

/

/Thomas KC P k /

M Parker Manager

. Nuclear Support Services c: Regional Administrator - Region III, NRC Senior Resident Inspector NRC-NRR Project Manager, NRC J E Silberg e