ML20010J279

Final Deficiency Rept Re Loss of Diesel Generator Output Due to Unit Tripping Out on Spurious High Crankcase Pressure Signals,Initially Reported on 810622.Correct Pressure Switches Installed & Calibr

ML20010J279
Person / Time
Site:	San Onofre
Issue date:	09/21/1981
From:	Papay L SOUTHERN CALIFORNIA EDISON CO.
To:	Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
References
10CFR-050.55E, 10CFR-50.55E, NUDOCS 8109300229
Download: ML20010J279 (3)

Text

. . 50.55(e) Report Docket Nos. 50-361/362 Southern California Edison Company R O. BOX 800 ST 2244 WALNUT GROVE AVENUE nOscucAo, cAurORNIA OWO m . .. ..- e September 21, 1981 ,,,..,,...,.

Mr. R.H. Engelken, Director Office of Inspe.ction and Enforcement N U.S. Nuclear Regulatory Commission [6 ' '

Region V  %

- 2 Suite 202, Walnut Creek Plaza E P 2 9 79 3 7 ,,,

1990 North California Boulevard D se j Walnut Creek, California 94596 Q' k

Dear Mr. Engelken:

y

Subject:

Docket Nos. 50-361 and 50-362 In a letter to your office dated June 22, 1981 we identified a condition involving loss of di sel generator out-put due to the unit tripping out on spurious high crankcase pressure signals. We considered this conditi0n to be potentially reportable in accordance with 10CFR50.55(e). On August 20, 1981 we provided an interim report related to the condition.

Enclosed in accordance with 10CFR50.55(e) are twenty -

five (25) copies of a final report entitled, " Final Report on Diesel Generator High Crankcase Pressure Signals, San Onofre Nuclear Generating Station, Units 2 and 3."

If you have any questions regarding this report, we would be pleased to discuss this matter with you at your con-veniance.

Very truly yours, Enclosures CC: Victoc Stello (NRC, Director I & E)

A.E. Chaffee (NRC, San Onofre, Units 2 & 3) g ni f?,

m m g 2 Ig8 f/ n.

" 51 hI r 1

S 9109300229 810921 PDR ADOCK 05000361 PDR S

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FINAL REPORT ON DIESEL GENERATOR HIGH CRANKCASE P'AESSURE SIGNALS San Onofre Nuclear Generating Station, Units 2 & 3 INTRODUCTION This final report is submitted pursuant to 10CFR50.55(e )(3). It describes a condition discovered during preoperational testing wherein spurious diesel generator trips occurred with "high crank-case pressure" on several of the engines. This report 7cludes a description of the situation, an analysis of the safety implications, and a summary of corrective actions taken to date. By letter dated June 22, 1981, Edison confirmed notification to the NRC of this potentially reportable condition. In a letter dated July 20, 1981, Edison reported that the. Investigation was incomplete and requested an extension on reporting time to August 21, 1981. An interim report was submitted to t'le NRC on August 20, 1981.

BACKGROUND During the diesel-generator;(D/G) preoperational test program, frequent high engine crankcase pressure alarms and trips were en-countered on engines of both D/G sets. Diagnosiic tests were con-ducted which determined the trips were spurious and did not reflect a true high pressure condition. A subsequent investigation revealed several causes and contributing factors.

DISCUSSION The following discussion is responsive to 10CFR50.55(e)(3).

Description,of the Deficiency These spurious trips were found to occur under a number of conditions:

(a) trips occurred randomly during engine operation, (b) trips occurred when the switches or mounting panel received any shocks or substantial vibration, and (c) trips occurred after engine shutdown j and would not clear to allow a restart. The investigation of the problem revealed several causes and contributing factors:

I a) The installed switches were found to be of the incorrect model and pressure range.

b) The sensing line was found to have low points which became filled with engine oil and caused erroneous input signals to the switches.

c) The repeatability of the switches was nat within specifica-tion.

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l Analysty of Safety Implications I The dier.al generators start automatically on either of Loss of Volt-age Signal (LOVS) or Safety Injection Actuation Signal (SIAS). The "high crenkcase pressure" trip is bypassed when a SIAS is present.

However, spurious "high crankcase pressure" trips during a LOVS condition without SIAS could trip one or both of the redundant diesel generators and preclude manual restart until the trip clears. Thus the diesel generators could be disabled during a loss of offsite power for events which do not result in a SIAS.

Corrective Action i The corrective action included the following:

1. The correct pressure switches have been installed and calibrated.

2. The sensing line size has been increased from 1/4 inch to 1/2 inch to preclude blockage and any capillary action.

The line was rerouted to avoid pockets and sloped to the engine to prevent oil entering the line.

3 A review was performed of the adequacy of the panel and switch support to' withstand vibration. The panel with the correct pressure switches has previously been seismically qualified. This qualification includes testing which sub-7 jected the panel to shocks and vibrations similiar to those described above without failure of the panel and the switches to perform their intended function.

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