ML20236Q531

Safety Evaluation Re Safety Limit Violation on 870911.Safety Significance Considered Low Due to Adequate Core Cooling & Low Decay Heat Levels.Basis for Conclusion Elaborated in Encl Insp Rept 50-219/87-29

ML20236Q531
Person / Time
Site:	Oyster Creek
Issue date:	11/06/1987
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20236Q524	List: IR 05000219/1987029 ML20236Q522 ML20236Q531 ML20236Q535 ML20236Q559 ML20236Q567
References
TASK-2.K.3.19, TASK-TM NUDOCS 8711200110
Download: ML20236Q531 (3)

See also: IR 05000219/1987029

Text

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION

RELATING TO THE SAFETY LIMIT VIOLATION ON SEPTEMBER 11, 1987

GPU NUCLEAR CORPORATION (GPUN)

OYSTER CREEK NUCLEAR GENERATING STATION

DOCKET NO. 50-219

1.0 INTRODUCTION

l

l In May of 1979, as a result of c1psing all five recirculation system valves

i simultaneously during a transient, a reactor zone water level transient

I occurred at Oyster Creek that went undetected until the receipt of the

low-low-low level alarm.

Soon after this incident, the NRC imposed a Safety Limit on the facility that

required at least two loops to have both the recirculation pump suction and

discharge valves open during all plant conditions unless the reactor vessel

, head was removed. Technical Specification P.1.E states, "During all modes of

I

operation except when the reactor head is off and the reactor is flooded to a l

1evel above the main steam nozzles, at least two (2) recirculation loop '

l suction valves and their associated discharge valves will be in the full open

position."

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l

As part of the post-Three Mile Island Action Plan, II.K.3.19, the NRC imposed

requirements for an interlock to prevent less than two loop operation. This

was subsequently changed to an alarm in the control room that would actuate if

I less than two recirculation loop suction and discharge valves were fully

l open. This alarm was installed during the recent (11R) refueling outage which

was completed in December 1986.

A violation of this Safety Limit occurred at Oyster Creek on September 11,

i 1987, when the plant was in cold shutdown and when fewer than two sets of

I

recirculation loop valves were fully open for a short period of time. The

operator closed the loop recirculation valves while responding to an event

involving a leak in the reactor building closed cooling water system. A

detailed description of the maintenance activities leading up to the event,

plant conditions immediately prior to the event and the sequence of events is

presented in the Region I Augmented Inspection Team Report No. 50-219/8749

(enclosed).

In letters dated September 20 and 22, 1987 the GPUN provided an analysis of the

event and GPUN's corrective actions (References 1 and 2). '

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2.0 EVALUATION  !

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The safety significance of this event is considered low based upon the analysis

of the events. The basis of the safety limit is to maintain fluid

communication between the core region and the annulus region of the reactor

vessel. The annulus region is where most of the level instrumentation measures ,

reactor vessel level. Only the fuel zone level instrumentation measures level 1

in the core region. Therefore, to accurately measure vessel level and activate .

the associated alarms and safety features, the Oyster Creek Techrical

'

i Specification requires at least two loops must be open to facilitate adequate

I fluid communication between the enre recion and the annulus. In our Safety

Evaluation on TMI ' action item IJ.K.3.io dated March 7, 1986, the staff

concluded that one loop is sufficient to assure adequete communication between

the core and downcomer recion during a plant shutdown. During shutdown

conditions at Oyster Creek, if no action is taken upon isolating all five

recirculation loops, it would take hours before boiloff o# water would lower

vessel level to the top of active fuel from the normal water level band given

the other conditions which existed at the time. These conditions are described

in AIT Report No. 50-219/87-29.

During the event, two isolation valves were opening as two isolation valves

were closing and, in addition, all five recirculation discharge bypass isola + ion

valves (2" valves) were full open. The analysis indicates that the time span i

from when the first isolation valve started to close until the second isolation

,

valve reached the full open position and cleared the less-than-two-loops-

l isolated alarm was approximately two minu+es. The maximum possible time

duration for this valve stroke sequence to occur would have been approximately

two and one half minutes. Therefore, considering actual valve stroke times and

time duration of the sequence, there was no time period durina which the core

region was completely isolated from the annulus region. In addition, the pump

discharge bypass valves were open throughout.

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3.0 CONCLUSION

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This event is considered a violation of the Safety Limit Technical

Specification, but its safety significance is considered low. The basis for

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this conclusion as elaborated upon in AIT Report No. 50-219/87-29 is that core

cooling was always adequate due to the low decay heat levels, fluid communication

! between vessel regions was always maintained and, in addition, the fuel rone

level instrumentation was functional and indicated that the fuel region water

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level was always maintained at appropriate levels for a shutdown reactor.

Reactor water level was always maintained at several feet above top of the

active fuel. There was no fuel damage or equipnent damaae during the event.

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d.0 REFERENCE

1. GPU letter, dated September 20, 1907 from P. R. Clark (GPU) to NRC

" Safety Limit Violation."

2. GPU letter, dated September 22, 1987 from P. B. Fielder (GPU) to NRC

" Spill of Reactor Building Closed Cooling Water during Maintenance."

Principal Contributor: G. Thomas

Dated: NOV o e 1997 ,

Enclosure: '

As Stated

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