ML20101F126

Special Rept Spr 920003:on 920516,smoke Detectors in Zone Ppp of Reactor Bldg Alarmed & Failed to Reset.Caused by High Temp & High Humidity & Detector &/Or Base Damage.Smoke Detector Sys Will Be Replaced in Mar 1993 During Refuel 7

ML20101F126
Person / Time
Site:	Summer
Issue date:	06/12/1992
From:	Skolds J SOUTH CAROLINA ELECTRIC & GAS CO.
To:	Ebneter S NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
SPR-920003, NUDOCS 9206240290
Download: ML20101F126 (4)

Text

.

south archnQ Electuc & 00s CompOny John 60 t gny sc mes w m o w annns

. SCE&G um. . -

June 12,1992 Mr. S. D. Ebneter Regional Administrator U. S. Nuc1 car Regulatory Coinmission Region II, Suite 2900 101 Marietta Street, NW Atlanta, GA 30323

Subject:

VIRGIL C. SUMMER NUCLEAR STATION DOCKET NO 50/395 OPERATING LICENSE N0. NPF-12 SPECIAL REPORT (SPR 920003) (ON0 920041)

This Special Report is being submitted by South Carolina Electric & Gas Company pursuant to the requirements of the Virgil C. Summer Nuclear Station (VCSNS) Station Administrative Procedure (SAP) 131A, fire Service Eauipment/

Systems Operability Requirements.

At 1230 hours0.0142 days <br />0.342 hours <br />0.00203 weeks <br />4.68015e-4 months <br /> on May 16, 1992, the smoke detectors in Zone PPP of the Reactor Building (RB) spuriously alarmed and failed to reset. Because of a previous failure of a smoke detector in the RB, hourly temperature readings required by the Action Statement of SAP-131A had previously been implemented.

During the Plant Safety Review Committee (PSRC) meeting of September 26, 1991, the failure of smoke detectors in the RB was discussed. The PSRC directed that a Root Cause investigation be initiated to determine a common denominator for the high failure rates of the RB smoke detectors. The task group identified two primary causes for the failures: high temperature and high humidity, in addition, secondary failure modes were identified which result in permanent detector and/or base damage. Attached to this report is a copy of the Executive Summary from the investigation.

A modification hn been initiated and approved for the replacement of the RB Smoke Detector System. This modification is currently scheduled for implementation in March 1993 during Refuel 7.

Should you have any questions, call at your convenience.

Very truly yours, John L. Skolds RJB:lcd l c: See Page 2 / v'9/ \

y \

9206240290 920612 PDR ADOCK 05000395 3 s PDR

Mr. S. D. Ebneter l

. Of40 920041 Page 2 of 2 c: 0. W. Dixon R. R. Mahan R. J. White General Managers G. F. Wunder S. R. Hunt NRC Resident inspector J. 8. Knotts Jr.

Marsh & McLennan Document' Control:-- Desk -

INPO Records Center ANI Library NSRC RTS ONO 920041)

File 818.05 & 818.08) l NOCLEAR EXCELLENCE - A SUMMER TRADITION!

.- . . - . . . . . ~ -

9

+

. Attachment to Mr. S. D. Ebneter Letter ON0 920041 Page 1 of 2-EXECUTIVE

SUMMARY

This Root Catse Investigation was initiated in response to a PSRC Committee request to d!termine a common denominator for the high failure rates of the Reactor Builjing Smoke Detectors. During this investigation, the task group identified two primary causes for the Reactor Building Smoke Detector failures. In addition, seconaary failure modes were identified which result in permanent detector and/or base damage.

The first primary failure contributor is high temperatures in the Reactor Building. A direct correlation can be made between smoke detectors experiencing high failure rates and platit locations with high ambient temperatures. In several failed detectors, the task group noted a general softening of a resin used in the assembly of the detector head. This softened resin allowed the internal detector components to shift or change configuration tolerances. Eventually, this changed internal configuration of the detector head will result in a false alarm signal. This softening of the resin is believed to be caused by extended exposure to the high area '

temperatures.

Another primary failure contributor is high humidity. Humidity levels experienced by the detectors located in the Reactor Building exceed those specified by the manufacturer. The high humidity caused the normelly energized trouble rel8y contacts to oxidize, eventually causing excessive line resistance and spurious trouble alarms. The detection strings with multiple detectors were especially vulnerable to this condition. The combination of high temperature and humidity is suspected to have a synergistic effect for the primary failure contributors. Radiation was considered as a possible contributing factor. However, no conclusive failure trend could be identified from the empirical data reviewed.

Detectors which fail in a locked trouble or alarm condition are susceptible to secondary failure modes. Design of the detectors and/or bases allows for operation in alarm or trouble condition for short durations only. Per the manufacturer, operator response and system reset would be expected to occur expeditiously. The detectors located in the Reactor Building are not readily accessible during normal plant operaticas, therefore detectors which lock into alarm or trouble may operate in these conditions for extended periods or until the next unit outage.

Several failed detector bases were inspected and tested by the task group.

Those bases which had operated continuously or over extended periods in alarm or trouble condition experienced wiring damage associated with the base's integral _ local buzzer. In addition, the detectors which had operated for extended periods in an alarm state experienced changes in the detector head's sensitivity. This sensitivity drift was found to be attributable to the cathode tube internal to the head. Once the detector's cathode tube fires, the tube remains in an energized / excited state. Extended continuous operation of the head in this state will result in changes in the required firing potential of the tube, hence causing the detector sensitivity to drift outside of the allowable range.

i

. Attachment to Mr. S. D. Ebneter Letter ONO 920041

. Page 2 of 2 Prior to this investigation Design Engineering was aware of the Reactor Building Smoke Detector reliability problem. Based on the poor system performance and vendor inability to support the existing system, modification MRF-20951 had been initiated and approved to repair or replace the plant smoke detector system. Implementation of the Reactor Building portion of this MRF is scheduled for Refuel 7.

The Reactor Building Smoke Detector failure Root Cause Investigation team concurs with the replacement of Reactor Building Smoke Detector System under MRF-20951. The new system components will be tested for operation in high _

radiation, temperature, and humidity environments. This modification should resolve the high failure rate problem currently being experienced by the Reactor Building Smoke Detectors.

m