ML20042E419

LER 90-007-00:on 900317 & 26,containment Ventilation Isolations Occurred During Purge Activities.Caused by Inadequate Procedural Guidance for Setpoint Determination. Alarm & Trip Setpoints increased.W/900413 Ltr

ML20042E419
Person / Time
Site:	Sequoyah
Issue date:	04/13/1990
From:	Bynum J, Spencer S TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-007, LER-90-7, NUDOCS 9004200753
Download: ML20042E419 (5)

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[ g c-TENNESSEE VALLEY' AUTHORITY; 6N 38A Lookout Place Chattanooga, Tennessee 37402-2801 April;13, 1990 ,

U.S. Nuclear Regulatory Commission I Washington, D.C. 20555 Attention: Document Control Desk-Centlement TENNESSEE VALLEY AUTHORITY - SEQUOYAH NUCLEAR PLANT UNIT 2 - DOCKET NO.

50-328 - FACILITY OPERATING LICENSE DPR LICENSEE EVENT REPORT (LER)-

50-328/90007 The enclosed LER provides details concerning two containment ventilation 1 isolations that occurred during purging activities as a result of radiation

-levels exceeding the calculated setpoint of the radiation monitors. These events.are being reported in accordance with 50.73(a)(2)(iv).

Very truly yours, TENNESSEE VALLEY AUTHORITY l . _ ,

.. R. Bynum, Vi e President Nuclear Power Production Enclosure '

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IhTO Records Center Institute of Nuclear Power Operatione 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 Commission Office of Inspection and Enforcement Region II 101 Marietta Street, Suite 2900 Atlanta, Georgia 30323 s

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On March 17 and 26, 1990, with Unit 2 operating in Mode 1 at 100 percent power, containment ventilation isolations (CVIs) occurred during containment purge activities.

Ibch of the CVIs resulted when actual radiation levels exceeded the calculated setpoint {

for Radiation Monitor (RM) 2-RM-90-130A. The root cause of the CVIs was procedures were b]ing used that did not contain appropriate guidance for setpoint determination when I cperating conditions such as elevated airborne radioactivity in containment are present. Immediate corrective actions consisted of verifying that a high radiation lovel did not exist in containment, recovery from the CVIs, and completion of new purge p;ckages. As long-term corrective action. TVA is increasing RM alarm and trip sstpoints, and requiring closer tolerance for adjusting instrumentation setpoints.

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p ngription of Event i At approximately 0645 Eastern standard time (EST) on March 17, 1990, with Unit 1 in Mode 3 (0 percent power, 2,235 pounds per square inch gauge (psig), and $47 degrees F) 7 cnd Unit 2 in Mode 1 (100 percent power, 2,235 psig, and 578 degrees Fahrenheit), a crntainment ventilation isolation (CVI) (EIIS Code JM) occurred on Unit 2. The CVI was ,

initiated by containment purge exhaust Radiation Monitor (RM) 2-RM-90-130A (EIIS Code IL) high radiation alarm when the setpoint was exceeded. The Unit 2 operator verified that containment purge was stopped and that the isolation valves were closed in cccordance with System Operating Instruction (SOI) 30.2, " Containment Purge System Operation." The automatic isolation of the CVI valves (EIIS Code ISV) resulted in the  ;

isolation of flow through the sample pump (EIIS Code P) for 2-RM-90-106 (lower ctmpartment RM) and 2-RM-90-112 (upper compartment RM). Operations personnel subsequently stopped 2-RM-90-106 and 2-RM-90-112 sample pumps. The Unit 2 unit operator ,

responded to the alarms, reset the high radiation alarm, and entered Limiting Conditions' for Operation (LCOs) 3.4.6.1 and 3.3.3.1 at 0645 EST. Operations personnel verified by

• indications in the main control room that both trains of CVI had actuated properly and vsrified that no actual high airborne radioactive conditions were present. '

Operations personnel proceeded with recovery steps for the CVI in accordance with

• S01 30.2 and S01-88.1, " Containment Isolation System." The CVI was reset, 2-RM-90-106 was returned to service, and LCOs 3.4.6.1 and 3.3.3.1 were exited at 0940 EST on March 17, 1990. Operations considered the caussi of the first CVI to have been '

ottributed to changing containment conditions during the elapsed time from abtaining the s mple until the actual purge was initiated. Operations requested Chemistry to resample end analyce the containment atmospheric conditions and initiate a new containment purge rolease package based on present conditions. Chemistry completed the requested purge p:ckage that contained the calculated setpoint for 2-RM-90-130A. The containment purge was successfully accomplished at 0600 EST on March 18, 1990.

On March 26, 1990, at approximately 0510 EST with finit 1 in Mode 5 (0 percent power, 0 psig, and 112 degrees F), and Unit 2 in Mode 1 (100 percent power, 2.235 psig, and 578 degrees F), a second CVI occurred during an attempt to purge Unit 2 containment.

The CVI was initiated by containment purge exhaust RM 2-RM-90-130A high radiation alarm sxceeding the setpoint ten minutes into the purge activity. The Unit 2 unit operator responded to the alarms, reset the high radiation alarm, and entered LCOs 3.4.6.1 and 3.3.3.1 at 0510 EST. Operations personnel verified by indications in the main control room that both trains of CVI had actuated properly and verified that no actual high airborne radioactive conditions were present.  ;

Operations personnel proceeded with recovery steps for the CVI in accordance with SOI 30.2 and SOI-88.1. The CVI was reset, 2-RM-90-106 was returned to service, and

• LCOs 3.4.6.1 and 3.3.3.1 were exited at 0515 EST on March 26, 1990. Operations considered the cause of the CVI to have been attributed to changing containment "

conditions during the elapsed time from obtaining the sample until the actual purge was initiated. Additionally, the containment atmosphere is a nonhomogeneous mixture, thereby permitting the purge to operate for approximately 10 minutes before the CVI NRC Fonn 3,tA (649)

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textm . w mic w am mim Description of Event (continued) cccurred. Operations requested Chemistry to perform a new containment purge package b: sed on present containment conditions. Chemistry completed the requested purge package, verified just prior to initiation of the second purge attempt that containment conditions had not changed, and the purge was successfully completed.

I Cause of Event The procedures used did not contain appropriate guidance for setpoint determination when operating conditions, such as elevated airborne radioactivity in containment are present. Additionally, the procedures used for adjustment of the M setpoints did not provide stringent acceptance criteria. Therefore, the M setpoint, which was 25 percent cbove the predicted M response, was not adequate to preclude the CVIs.

Analysis of Event These events are reportable in accordance with 10 CiR 50.73, paragraph (a)(2)(iv) as an engineered safety feature actuation, which was not part of a preplanned activity.

Following the CVIs, Operations personnel took appropriate and timely action in verifying that the trip setpoints were exceeded and that actual high airliorne radioactivo conditions in containment did not exist. Upon receipt of the OVI signals, the equipment roquired to actuate on a CVI signal performed as designed. Because actual high airborne radioactive conditions did not exist, (27.3 percent of technical specificativn [TS) limits for the first event and 38.8 percent of TS limits for the e cond eve,nt), there was no threat to plant personnel or the general public. Therefore, nu adverse safety consequences resulted from this event.

Corrective Action As immediate corrective action for each event, Operations personnel verified that a high l cirborne radioactive condition did not exist. Operations recovered from the CVIs in

! cecordance with SOI-30.2B, requested initiation of new purge packages, and performed l' successful purges.

As interim corrective action, Chemistry is sampling containment atmosphere just before initiation of containment purge activities. This provides added absurance that containment conditions have not changed.

As long-term corrective actions:

, 1. Chemistry has evaluated the setpoint criteria for the alarm and trip setpoints on l- the 1, 2-M-90-130A and -131A Ma and are revising Surveillance Instruction l (SI) 410.2, " Containment (Upper, Lower) Purge," to allow higher setpoints that are still well below TS limits. SI-410.2 will be revised by May 7, 1990.

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Corrective Action (continued)  ;

2. Technical Support has compared the actual RM setpoint acceptance criteria in SI-291.3, " Readjustment of Setpoint for Radiation Monitors with Variable Setpoints and Block I' unctions," with the acceptance criteria in SI-83. " Channel Calibration for' Radiation Monitoring System," and determined that SQN can reduce the uncertainty in establishing setpoints. Technical Support has revised SI-291.3 to require tighter acceptance criteria for radioactive effluent and containment radiation ,

monitors.

Additional Information These are the first CVIs resulting from increased airborne radioactive conditions during I containment purge.

, C?mmitment SI-410.2 will be revised to allow higher setpoints for RMs by May 7, 1990, t

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