ML20213G707

Special Rept:On 861020,condenser Evacuation Sys wide-range Noble Gas Monitor RI-7870 mid/high-range Channel Indication Found to Be Oscillating & Monitor Removed from Svc.Caused by Failed Preamplifier Circuit Board Due to Aging

ML20213G707
Person / Time
Site:	San Onofre
Issue date:	11/06/1986
From:	Morgan H SOUTHERN CALIFORNIA EDISON CO.
To:	Martin J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V)
References
NUDOCS 8611180278
Download: ML20213G707 (2)

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hd Southern California Edison Company SAN ONOFRE NUCLEAR GENERATING STATION P O. BOX 128 SAN CLEMENTE. CALIFORNIA 92672 H E MORGAN November 6, 1986 g["g, U. S. Nuclear Regulatory Commission _

Office of Inspection and Enforcement o, Region V .

1450 Maria Lane, Suite 210 ,

Walnut Creek, California 94596-5368  ; g Attention: Mr. J. B. Martin, Regional Adminstrator } -

3 $

Dear Sir:

~~

Subject:

Docket No. 50-362 ~

Special Report San Onofre Nuclear Generating Station, Unit 3 In accordance with Technical Specification 6.9.2 and Table 3.3-6, Action Statement 19, of Facility Operating License No. NPF-15 for San Onofre Nuclear Generating Station, Unit 3, this letter provides the required Special Report for the Condenser Evacuation System Wide Range Noble Gas Monitor being out of service greater than 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.

On 10/20/86, at 1100, with Unit 3 in Mode 3, Condenser Evacuation System Wide Range Noble Gas Monitor 3RI-7870 mid/high-range channel indication was found to be oscillating, and the monitor was removed from service. Repairs were completed and the monitor was returned to service on 10/30/86 at 1810 after successful completion of the quarterly surveillance.

The cause of the monitor oscillations was traced to the preamplifier circuit board for the mass flow transducer which is believed to have failed due to accelerated aging resulting from elevated temperatures, as evidenced by discoloration of the circuit board. The board is being returned to the manufacturer for additional analysis. The transducer set and the circuit board (Kurz ME-1661) were replaced.

The lead shield enclosure for this monitor impedes heat dissipation and creates an elevated temperature environment which accelerates aging of the solid state components . Interim corrective action will be taken to periodically replace this circuit board based on the expected mean time between failures. During the perfornance of radiation monitor surveillance testing, other circuit boards operating in a similar environment will be inspected, and suspect boards will be replaced. An evaluation is being conducted for this circuit board, and other boards that may be affected, to determine if components should be relocated, or if cooling should be provided for the enclosure.

0611180278 861106 PDR ALOCK 05000362 S PDR EO p' ';/

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Mr. J. B. Martin -

2-The health and safety of plant personnel or the public was not affected, as no release was involved, and alternate monitoring was provided as required by the Technical Specifications.

Please contact us if we can be of further assistance.

Sincerely, Mb Enclosure cc: F. R. Huey (USNRC Senior Resident Inspector, Units 1, 2 and 3)

U. S. Nuclear Regulatory Commission Document Control Desk Institute of Nuclear Power Operations (INPO)

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