05000361/LER-1984-023, :on 840524,spurious Actuation of Control Room Isolation Sys Occurred Because of Noise Spike on Control Room Airborne Radiation Monitor.Monitor Detector Replaced & Preamplifier Properly Grounded

:on 840524,spurious Actuation of Control Room Isolation Sys Occurred Because of Noise Spike on Control Room Airborne Radiation Monitor.Monitor Detector Replaced & Preamplifier Properly Grounded

ML20138N579
Person / Time
Site:	San Onofre
Issue date:	11/01/1985
From:	Morgan H SOUTHERN CALIFORNIA EDISON CO.
To:
Shared Package
ML20138N558	List: 05000361/LER-1984-023, :on 840524,spurious Actuation of Control Room Isolation Sys Occurred Because of Noise Spike on Control Room Airborne Radiation Monitor.Monitor Detector Replaced & Preamplifier Properly Grounded 05000361/LER-1985-019, :on 850517,fuel Handling Isolation Sys Actuated by Spurious Airborne Monitor Alarm.Probably Caused by Radiation Monitor Detector Sensitivity.Spurious Actuations Also Occurred on 850519,26 & 0607 ML20138N556
References
LER-84-023, LER-84-23, NUDOCS 8511050235
Download: ML20138N579 (1)

LER-1984-023, on 840524,spurious Actuation of Control Room Isolation Sys Occurred Because of Noise Spike on Control Room Airborne Radiation Monitor.Monitor Detector Replaced & Preamplifier Properly Grounded

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(viii) 10 CFR 50.73(a)(2)(x)
3611984023R00 - NRC Website

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NR'C FJint 346 U.5L NUCLEA:'t REGut.ATOAY COMMISSION APPROVED OMS NO. 31504104 LICENSEE EVENT REPORT (LER)

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l CONTROL ROOM ISOLATION SYSTEM (CRIS) ACTUATIONS

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On May 24,1984, at 0952, with Units 2 and 3 in Mode 1 at 100% and 90% power, r:spectively the Control Room Isolation System (CRIS) (EIIS System Code VA) Train 'B' was spuriously actuated from a noise spike on Control Room Airborne Radiation Monitor 2/3RE-7825 (EIIS Component Code RIT). subsequent CRIS actuations occurred on May 27, June 20, and June 21. On each occurrence the Control Room Emergency Air Cleanup System (CREACUS) (EIIS System Code VI) actuated as required. Operators used the i

respective. redundant Control Room Airborne Radiation Monitors and air grab samples to verify that. actual Control Room radiation levels were below the CRIS actuation setpoints before resetting the CRIS and securing the CREACUS. See also.LERs84-002, 038, 047, and 073 (Docket No. 50-361), and 86030 (Docket No. 50-362).

Investigation has determined that the most probable single cause of the actuations was ground current surges traveling to the monitors through the ground system. An i ~

' additional-investigation of the' grounding system has been completed.

It has been cencluded the noise surges were entering through the detector and preamplifier. The detector was replaced and the preamplifier was properly grounded. This reduced the naise significantly, and the number of spurious actuations has been reduced to an infre~quent level, t

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