ML19225C429

Submits Info Requested in 780807 Ltr Re Reactor Protection Sys Power Supply.Ge Has Conducted Failure Modes & Effects Analysis & Seismic Performance Evaluation Test & Concluded Risk of Failure Is Low.No More Studies & Mods Required

ML19225C429
Person / Time
Site:	Vermont Yankee
Issue date:	07/27/1979
From:	Moody D VERMONT YANKEE NUCLEAR POWER CORP.
To:	Ippolito T Office of Nuclear Reactor Regulation
References
WYV-79-83, NUDOCS 7907300305
Download: ML19225C429 (2)

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{ V ERMONT Y AN KME NUCLEAR POWER CORPORATION stvCNTY SEVEN GROVC STR ECT B.3.2.1 RUTI. AND, VEltM O NT 05701 WY 79-83 REPLY TO:

ENGINEERING OFFICE TURNPlK C RO Ao WESTDORO, M AU3 AcHUSCTTS 01581 July 27, 1979 ytte, sour.,,.3...,o,,

United States Nuclear Regulatory Commission Washington, D.C. 20555 -

Attention: Office of Nuclear Reaccor Regulation Thomas A. Ippolito, Chief Operating Reactors Branch #3 Division of Operating Reactors Re fere. ice s : (1) License No. DPR-28 (Docket No. 50-271)

(2) USNRC Letter to YAEC dated August 7, 1979 (3) VYNPS Letter (WVY 78-92) to USNRC. dated October 11, 1979

Subject:

Reactor Protection System Power Supply Reference (2) identified certain concerns regarding the Reactor Protection System Motor-Generator Sets, wherein a unique sequence of events is postulated to adversely af fect the operability of the Reactor Protection System. We were asked to evaluate our system and determine whether the same characteristics as those identified in Reference (2) were possible following a similar chain of events.

Our responsc, Re fer ence (3), was based on preliminary information from the General Electric Company which indicated that although the chain of events postulated in Reference (2) was technically possible, this unique combination and sequence of events had an extremely low probability of occurring and thus was not a problem which required any modifications to the Reactor Protection System. In order to support this position, we stated that General Electric was in the process of performing a Failure Modes and Effects Analysis; and, in addition qualification work was in progress to evaluate the capabilities of the install.ed equipment. We committed to inform you of our position on completion of the above e f forts.

General Electric has since conducted; (1) a Failure Modes and Effects Analysis (FMEA), where hypothesized single and common mode failures are analyzed and; (2) a seismic performance evaluation test where a specimen of an RPS MG Set Protective Circuit was tested under simulated sei mic conditions on a shaker table. Based on the se two programs , General Elec*r - 'oncluded with r

the following statemeats:

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United States Nuclear Regulatory Commission Page 2 July 27, 19'/9 L

"The FMEA summary concludes that the risk of an RPS failure with the present design is sufficiently low and acceptable" and "The seismic performance test ... concludes that the specimen demonstrated sufficient integrity to withstard the prescribed simulated seismic event environment without compromise if structure or electrical functions."

Based on the information contained in these studies, together with the minor equipment modifications made to satis fy the calibration requirements of Re ference (2), we conclude that no additional studies or modifications are required.

In ordcr to satisfy concerns associated with the postulated single failure of motor generator set equipment, we will continue to perform the surveillance and testing outlined in Reference (3).

We trust that the information provided above is adequate to close out this issue; however, should you have any questions, do not hesitate to call.

Very truly yours, VERMONT YANKEE NUCLEAR POWER CORPORATION

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D. E. Moody W

Manager of Operations DEM/jgh 414 3;3]p