ML20137V742
| ML20137V742 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 11/25/1985 |
| From: | Morgan H SOUTHERN CALIFORNIA EDISON CO. |
| To: | Martin J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| References | |
| NUDOCS 8512100074 | |
| Download: ML20137V742 (2) | |
Text
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S Southern California Edison Company SAN ONOFRE NUCLEAR GENERATING STATION P. O. BOX t 28 SAN CLEMENTE, CALirORNIA 92672 H. E. MORGAN -
TELEPHONE S
ON M A N AGE R November 25, 1985
<7388-****
U. S. Nuclear Regulatory Commission
~0ffice of Inspection and Enforcement
-Region V 1450 Maria Lane, Suite 210 Walnut Creek, California 94596-5368 Attention:
Mr. J. B. Martin, Regional Administrator
Dear Sir:
Subject:
Docket No. 50-206 Special Report - Revision 2 San Onofre Nuclear Generating Station, Unit 1
Reference:
Special Report - Revision 1, H. E. Morgan (SCE) to J. B. Martin (NRC), Same Subject, dated October 15, 1985 Pursuant to Section 6.9.3.f of Appendix A, Technical Specifications to Provisional Operating License No. DPR-13 for San Onofre Unit 1, the referenced letter provided a Special Report on inoperable radiation monitoring instrumentation. This letter provides an update on the-continuing investigation and additional corrective actions taken subsequent to the referenced letter.
On August. 14, 1985, at 0925 with Unit I at 93% power, the High Range West Main Steam Line Radiation Monitor R-1258B failed low and was removed from service.
The preplanned alternate method of monitoring was initiated at 1311 in accord-ance with Limiting Condition for Operation (LCO) 3.5.10, Action Statement 27.
The Low Range West Main Steam Line Radiation Monitor and both High and Low Range East Main Steam Line Radiation Monitors have remained operable.
As reported in the referenced letter, our initial assessment postulated that a ground loop was responsible for the instrument failure.
However, subsequent to our letter, a grounding study was completed which showed no apparent design discrepancies in the instrument grounding scheme. A poise study was also performed which demonstrated the probable causenofft'Se problem is AC noise induced into the coaxial detector I/O cables." Also, in an effort to rule out possible " shorts" etc., the 50 pin input / output (I/0) D g-cat connector has been replaced.
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4 Mr. 'J. B. Martin I As a result of the new information obtained from the grounding and noise studies we were unable to return Monitor R-1258B to service by November 1, 1985. On November 7, 1985, we scheduled corrective actions to correct the signal noise problem during the upcoming Cycle IX refueling, scheduled to begin November 30, 1985.
Neither the health and safety of plant personnel nor the health and safety of the public was affected by this event.
If you require additional information, please so advise.
Sincerely, b
L cc:
F. R. Huey (USNRC Senior Resident Inspector, Units 1, 2 and 3)
U. S. Nuclear Regulatory Commission i
Document Control Desk Institute of Nuclear Power Operations (INP0) 1 e
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