ML20045A393

LER 91-029-01:on 911130 & 1213,false Primary Containment High Radiation Isolation Sys Occurred.Caused by Filters Attached to Input of Monitors.Correct Operation of Isolation of Primary Containment Vent & Valves confirmed.W/930603 Ltr

ML20045A393
Person / Time
Site:	FitzPatrick
Issue date:	06/03/1993
From:	Mulcahey E, Harry Salmon POWER AUTHORITY OF THE STATE OF NEW YORK (NEW YORK
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
JAFP-93-0318, JAFP-93-318, LER-91-029, LER-91-29, NUDOCS 9306100190
Download: ML20045A393 (5)

Text

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i Jamss A.FitzPctrick i

= Nuclear Powir Pl:nt ..

P.O. Box 41 Lycoming, New York 13093 j 315 342-3840 i

1. > NewYo.rkPower Harry P. Salmon, Jr.

& Authority nesieeni uenege, l

June 3, 1993 i JAFP-93-0318

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United States Nuclear Regulatory Commission i Document Control Desk i Mail Station P1-137 Washington, D.C. 20555 )

SUBJECT:

DOCKET NO. 50-333 LICENSEE EVENT REPORT: 91-029 Spurious Trips of Primary Containment Vent and Purge Isolation System

Dear Sir:

This updated report is submitted in accordance with 10 CFR 50.73 (a) (2) (iv) .

Questions concerning this report may be addressed to Mr. Eric Mulcahey at (315) 349-6458.

Very truly yours,

/ , f IARRY P.' SALMON, J W .

HPS. M: tid Enclosure cc: USNRC, Region i USNRC Resident Inspector INPO Records Center 9

93051'00190 930603 i PDR ADDCK 05000333 S PDR .\

NRC FORM 3t,1I U.S NUCLE AR RE GUI.ATORY COMMISSION 1,6 Sp APPROVED OMB190 3150 0104 E XPIRE S 4/30/92 ESTIMATED BURDEN 8'E R RESPONSE TO COMPL Y WTH THIS LlCENSEE EVENT REPORT (LEF SIMvENIs'UGNo'i'G fu7 o"MEsV[uAYE "%'RICO Os AND REPORTS MANAGEMENT BR ANCH IP 5308, U.S NUCLE AR HEGUL ATORY COMMIS510N. W ASHa3 TON. DC 20555. AND TO THE PAPERWORK RE DUCitON PROJECT (31500104). OFF ICE OF MANAGEMENT AND BUDGET. WASHINGTON. DC 20503 FQCtLITY NAME (1) DOCKET NUMBE R (2) F AGE 43 James A. FitzPatrick Nuclear Power Plant o l5 ; O io ; o l3i 3 } i lorlc) g TITLE tai Spurious Trips of Primary Containment Vent and Purge Isolation Systen EVENT DATE (51 LER NUMBER (6) REPORT DAT E 471 OTHE R F ACILITIES INVOLVED 18)

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Update Report - Previous Report Date, Janubry 2, 1992 EIIS Codes are in []

False primary containment [NH] high radiation isolation system [JM]

signals occurred at 1431 and 1938 on November 30, 1991, and again at 1114 on December 13, 1991, while the reactor was shutdown in the cold condition. The 12 primary containment isolation valves which are activated by these signals were already closed or went closed in response. Before two of the actuations, a two-way radio was being keyed in the vicinity of the radiation monitors and at the time of the third, a cable penetration fire seal inspection was being conducted within the monitor cabinet and a Technical Specification surveillance test was being performed on main steam line radiation monitors located in adjacent cabinets. The pathways for initiation of the monitor trips was through a filter assembly. The filters were found attached to the input of the monitors during a root cause investigation. The filters were removed from the monitor inputs before the plant was restarted in January, 1993, to eliminate monitor trips by this pathway. The root cause investigation and analysis was completed during the 1992 Refueling Outage.

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Description While the reactor was shutdown and in a cold condition on November 30, 1991, two invalid actuations of the primary containment [NH] vent and purge valves isolation system occurred. The first actuation was initiated at 1431 by the primary containment high range radiation monitor [JM] channel A and the second initiated at 1938 by high range radiation monitor channel B. At 1114 on December 13, 1991, with the reactor still in the cold condition, high range radiation monitor channel A again initiated an invalid isolation of the primary containment [NH] vent and purge valves system.

Just before the November 30, 1991, actuations a two-way radio was being keyed in the proximity of the control room cabinets containing the high range radiation monitors. The 1431 actuation, initiated the tripping of division I (channel A) isolation logic circuity (outboard vent and purge valves) and the 1938 actuation initiated the tripping of division II (channel B) isolation logic circuity (inboard vent and purge valves). During the December 13, 1991 actuation, two work  ;

activities were being conducted within the vicinity of the Primary l Containment high range radiation monitors, one was the performance of l a Technical Specification (TS) table 4.1-2 Main Steam Line Radiation '

Monitor channel A calibration surveillance and the second was a fire seal inspection of cable penetrations by craft electricians within the cabinet containing the monitors. Two attempts to repeat the actions ,

of the craft electricians failed to reproduce an actuation of the monitors and the surveillance testing was continued without further incidence of spurious actuation of the high range radiation monitors.

At tne conclusion of each actuation, the isolation logic was reset and occurrence reports (OR) initiated by the station operators.

l Cause After experiencing repeated actuation of the primary containment [NH]

vent and purge isolation systems and also other ventilation systems caused by spurious (invalid) initiation of radiation monitors, a radiation monitoring specialist was contracted to perform a field investigation and analysis of the causes. A study was conducted during the 1992 refueling outage. The specialist started a NRC Form 366A (Mt91

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.aem a cr- w.nm preliminary inspection of the monitors environment, circuitry configuration and interconnection relationships on December 9, 1991. -

The primary containment high range radiation monitors with a high number of random actuations were selected to be investigated first, studying the sensitivity of the monitors to external (electrical and magnetic) noise. A possible pathway for the introduction of the noise into the input of the monitors had been identified from.the preliminary investigation. In LER-91-030, it was described as a filtering network attached to the inputs of the high range radiation monitors which is believed to have been used for evaluations of Electromagnetic Interference (EMI) during field tests. In-depth analysis was performed to quantify the effect of the filter assembly on the monitors performance.

The filter was found to have a significant effect on EMI susceptibility. The assembly was poorly shielded and the assembly design was such that it would rectify (and the monitor would amplify) any EMI induced noise. This was verified by keying a hand held radio to demonstrate the EMI susceptibility of the circuit with and without the filter in place.

Analysis The activation of the primary containment vent and purge valves isolation logic is reportable under provisions of 10CFR50.73 (a) (2) (iv) as an actuation of an Engineered Safety feature [JE]. There were no system or equipment failures. The 12 isolation valves which received the close signal were already in the closed (isolated) position or went closed (isolated) when actuated by the logic circuitry. The isolation logic initiating signal was not a true high radiation signal. There was no potential for adverse safety consequences generated by this event.

Corrective Actions

3. Correct operation of the isolation of the primary containment vent and purge valves system was confirmed. The isolations were then reset and occurrence reports initiated.

2. The Control Room operators removed the two-way radios from the Control Room and posted signs on Control Room [NA] entrance doors warning against use of radios in the Control Room.

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3. The attached filter to the high range radiation monitors was removed prior to restart after the 1992 Outage, also the signal input cables were shortened and rerouted to lessen adverse effects of Electromagnetic Interference (EMI).

I Additional Information Related LERs: 90-028 An electrical noise spike resulting from a l high voltage measurement on a radiation monitor caused a partial isolation of the reactor building (secondary containment) [NG]

ventilation system.91-001 An electrical noise spike resulting from a high voltage measurement on service water effluent (KG] process radiation monitor caused primary containment high range radiation monitor B to initiate an isolation of primary containment vent and purge isolation valves.91-018 A random electrical noise spike (source unknown) caused primary containment high range monitor A to initiate an isolation of primary containment vent and purge isolation logic circuitry.91-022 A spurious noise spike believed to have been generated by an isolation delay timer caused primary containment high range radiation monitor A to initiate an isolation of primary containment vent and purge isolation logic circuitry.91-030 Assemblies (fi]*ers) on the input of the primary containment high range radiation monitors have been the cause of the spurious isolations of the vent and purge valves.

Reason for Update: This LER is updated to provide the results of the j evaluation of the effects of the filter assembly found attached to the input to the primary containment high range radiation monitors. A vertical bar in the right hand margin indicates text changes (except where minor editorial or typographical errors were corrected.

NRC Form 366A 16494

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