ML20043E540

LER 90-008-00:on 900514,two Control Room Isolations Occurred as Result of Spurious Spikes.Caused by Loose Terminations on Relay Socket.Loose Connections Properly terminated.W/900607 Ltr

ML20043E540
Person / Time
Site:	Sequoyah
Issue date:	06/07/1990
From:	Bynum J, Spencer S TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-008-01, LER-90-8-1, NUDOCS 9006130109
Download: ML20043E540 (5)

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TENNESSEE VALLEY AUTHORITY

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. Chattanooga, Tennessee 37402-2801 June 7, 1990 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Gentlemen:

TENNESSEE VALLEY AUTHORITY - SEQUOYAH NUCLEAR PLANT UNIT 1 - DOCKET NO.

50-327 - FACILITY OPERATING LICENSE DPR LICENSEE EVENT REPORT (LER) 50-327/90008 The enclosed LER provides details of events wherein two control room isolations occurred as a result of spurious spikes caused from loose terminations on a relay socket for Radiation Monitor 0-RM-90-126. These events are being reported as engineered safety feature actuations in

.accordance with 10 CFR 50.73(a)(2)(iv).

Very truly yours.

TENNESSEE VALLEY AUTHORITY

/

. R. Bynum, Vice President Nuclear. Power Production Enclosure cc (Enclosure):

INPO Records Center Institute of Nuclear Power Operations 1100 Circle 75-Parkway, Suite 1500 Atlanta, Georgia 30339 NRC Resident Inspector Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy Daisy, Tennessee 37379 Regional Administration U.S. Nuclear Regulatory Comission Office of Inspection and Enforcement Region II 101 Marietta Street, Suite 2900 Atlanta, Georgia 30323

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Radiological Control personnel immediately surveyed the aseta and determined that no abnormal activity levels existed in the area. Operations personnel reset the CRIs after each respective isolation. Both of the CRIs resulted from high radiation spikes on Radiation Monitor (RM) 0-RW 90-126. The initial CRI appeared to be caused from welding or an unknown radie frequency source. After the second CRI, subsequent investigation revealed the root cause to be loose terminations on a relay socket that had been replaced dur!.ng the outage. The loose terminations generated noise resulting in a CRI when disturbed by personnel who were working near the loose terminations. Intermediate corrective actions consisted of properly terminating the loose connections on the relay s:,cket anf .tiew of the strip charts of the other RMs that had relay sockets replaced to ensure indications of exceasive noise that would be indicative of improper terminati . As long-term corrective action, SQN has implemented a comprehensive 7 program reduct. personnel errors.

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0 10 0 12 0F 014 TEXT U passe ausse 4 *seuseet es. eslisawier WC Aenen JIBCa, Oh Description of Event At 0900 Eastern daylight time (EDT) on May 14, 1990, with Unit 1 in Mode 5 (0 percent power. 300 pounds per square inch gauge (paig), and 170 degrees Fahrenheit (F)), and Unit 2 in Mode 1 (100 percent power, 2.235 psig and 578 degrees F) a control room isolation (CRI) occurred as a result of a spurious spike on a control room intake rcdiation monitor-(RM). At 2016 EDT on May 21,*1990, with Unit 1 in Mode 5 (0 percent power, 300 psig, and 170 degrees F), and Unit 2 in Mode 1 (100 p m ent power, 2,235 psig, and 578 degrees F), a second CRI occurred as a result of a spurious spike on a control room intake RM. In both cases. Operations immediately entered Limiting Condition for Operation (LCO) 3.7.7 and dispatched Radiological Control personnel to oscertain if an actual high radiation condition existed. The CRIs were both initiated f rom RM (F11S Code IL) 0-RM-90-126, which samples the main control room air intake.

This RM supplies an input signal to the Train B of the control room emergency v:ntilation system (CREVE) (EIIS Code VI). In both events. Radiological Control surveys rsveeled that an actual high radiation condition did not exist, the CR!s were reset in cecordance with System Operation Instruction (S01) 30.1B. " Isolation of the Control Room Heating Air Conditioning, and Ventilation System." and LCO 3.7.7 was exited at 0955 EDT on May 14 and 2045 EDT on May 21, 1990, respectively.

Investigation of the first event consisted of the followingt (1) The instrument mechenics checked the power supplies for proper voltage output and noise, (2) the shift operations supervisor (SOS) interviewed Electrical Modifications personnel working in the area to determine if the work being performed could have caused the CRI, and (3) the SOS interviewed the shift operations personnel to determine if any switching or motor starts were being performed during this time. The system engineer and the factory representative for the RM manufacturer (Sorrento) were in the area at the time of the svent and saw the spike trace. The system engineer and the factory representative both reviewed the trace, and both considered the trace to be representative of welding noise. Based on the above and the results of the radiological surveys, it was concluded that the initial CRI was caused from welding or an unknown radio frequency source.

Accordingly, the RM was returned to service.

Following the second event, a more indepth investigation into peripheral activities was conducted. It was determined that a relay socket for the RM had been recently replaced; the RM was declared operational on May 12, 1990, after the performance of the postmodification test (PMT). The PMT did not indicate problems existed in the system.

The PMT was written to perform response time testing of the newly-installed relay; a review of the strip charts was not required because no changes were made to the strip chart circuit. Review of the strip chart for RM-90-126 following the second event back to May 12, 1990, indicated numerous instances where spikes occurred. It is believed that while personnel were working in the panels near the loose terminations, these loose terminations would cause spikes on 0-RM-90-126. similar to those caused by welding or a radio frequency signal.

Cause of Event The root cause of the first event is ettributed to personnel error in that during the wiring termination for the relay socket, the individuals failed to tighten the terminations properly. The root cause of the second event is attributed to a lack of depth during the review of the first CRI. The individuals involved in the review of the nc . senA nei

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Cause of Event (Continued) first CRI looked at the activities occurring during the incident, reviewed the RM strip chart and, from past experience, concluded that welding caused the event and failed to further investigate the event.

Analysis of Event These events are being reported in accordance with 10 CFR 50.73(a)(2)(iv), as unplanned-cetuations of an engineered safety feature.

The main control room habitability system, is described in Section 6.4 of the SQN Updated Final Safety Analysis Report (UFSAR). The control building air-cleanup system cnd the heating, ventilation, and air-conditioning system are described in Section 9.4.1 of the UFSAR. Additionally, the main control room air intake RMs are described in Ssetion 11.4.2.2.5 of the UFSAR. The CREVS is designed to provide a safe environment for personnel controlling plant operations during normal operations and during cecidents. There are two 100-percent redundant equipment trains for CREVS--Train A and Train B. The function of the subject RM is to detect high radiation levele in the main control room air intake and, upon detecting high radiation levels, to initiate a CRI, cnd subsequent CREVS start to protect the main control room environment from contamination. In each of these events, the RM performed its design function to initiate isolation of the main control room and CBEVS actuation. Associated equipment performed its intended function as designed. The loose wiring caused the RM to operate in the conservative direction, i.e., to initiate the protectivo function. Because there wIs no actual radiation increase involved with these events, there was no adverse effect on the health and safety of the public or plant personnel.

Corrective Action Iimediate corrective actions for each event consisted of having Radiological Control parsonnel perform surveys to ensure actual high radiation conditions did not exist and recovering from the CRIs in accordance with S01-30.1B.

After it was determined that loose terminations were the cause of the spikes, the loose terminations were properly terminated. The strip charts of other RMs that had the relay sockets replaced were reviewed to ensure that other instruments were not reading crratically. In addition, functional tests have been performed on the Unit 1 and Unit 2 upper and lower containment RMs and the A and B trains of the control room intake RMs to ensure these RMs are functioning properly. It is believed that these loose terminations '

were an isolated incident. Personnel performing the incident investigation have been cautioned to fully examine all possible causes, i.e. not always believe the seemingly most obvious conclusion. Management emphasis is continuing to be placed on reducing personnel errors as described in LER 50-328/90008.

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Consnitment s None.

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