ML20090D826

AO-50-219/75-04:on 750303,average Planar Linear Heat Generation Rate Limits for Fuel Types III-E & F Exceeded Tech Specs Due to Unplanned Insertion of Control Rod 26-43. Caused by Relay 4k2 Failure.Relay Replaced

ML20090D826
Person / Time
Site:	Oyster Creek
Issue date:	03/10/1975
From:	JERSEY CENTRAL POWER & LIGHT CO.
To:	NRC
References
AO-50-219-75-04, AO-50-219-75-4, NUDOCS 8303020433
Download: ML20090D826 (4)

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Jers'ey Central Power & Light Company U(

MADISON AVENUE AT PUNCH BOWL ROAD e MORRISTOWN, N.J.07960

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OYSTER CREEK NUCLEAR GENERATING STATION FORKED RIVER, NEW JERSEY 08731 Abnormal Occurrence '

Report No. 50-219/75-4  ?

Report Date

('\ l March 10, 1975 N.

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Occurrence Date March 3, 1975 j l

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Identification of Occurrence }

1 A malfunction in the Reactor Manual Control System (unplanned insertion of N control rod 26-43) caused the Average Planar Linear lleat Generation P. ate Limits for fuel types ITI-E and III-F to be exceeded. This event is con-sidered to be an abnormal occurrence as defined in the Technical Specifications, paragraph 1.15B.

Conditions Prior to Occurrence The plant was operating at steady-state power with major parameters as follows:

Power: Reactor,1837.3 FMt Electric, 647 MWe Flow: Recirculation, 55.3 x 106 lbm/hr Feedwater, 6.85 x 10 6 lbm/hr Stack Gas: 32,550 uci/sec Description of Occurrence J

On Monday, March 3, 1975, at 0137, during the course of the weekly control rod

.. exercise surveillance, control rod 26-43 had been properly inserted one notch from position 48 (fully withdrawn) to position 46. Upon the attempt to withdraw it to position 48 using the manual rod control switch, control rod 26-43 inserted ,

from position 46 to position 28, stopping only after several attempts to withdraw using " notch override" in conjunction with the manual rod control switch and finally reducing the control rod drive water pressure.

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AbnormalOccurrc()ReportNo. 50-219/75-4

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The insertion caused the linear heat generation rates in fuel assemblies surrounding location 26-43 to increase sharply in the upper portion of the core as the control rod approached and stopped at the same position as two

, adjacent rods, 22-43 and 30-43 (see Figure 1) .

After consultation with the Technical Supervisor, the following corrective action was taken:

1. At 0145, rod group 22 was inserted from position 28 to position 24 to help reduce the flux peaking. At this time it was not known whether the normal rod control circuit would function, therefore, the " emergency rod-in" switch was used. The peak was reduced significantly at position 24 with only slight increases at nodes above position 24.

2. Consideration was now given to attempt the withdrawal of rod 26-43.

Since movement of the rod in either direction (in or out) would have the cifect of lowering the local power levels, it was decided to make the withdrawal attempt using the manual rod control switch. Rod 26-43 was successfully withdrawn by this means to position 48 at 0151.

3. Group 22 was then successfully withdrawn to its original position (28) using manual notch withdraw at 0155. TIP traces were taken immediately after the event and throughout the corrective action for subsequent analysis.

Observation of the Off-Gas Monitors revealed no increase in the release of activity indicating that fuel failure had not occurred.

After the return to the original rod pattern, an Instrument Technician was called to the site to determine the cause of the rod insertion. Upon hia arrival, the control rod exercise surveillance was continued and operation of the manual rod control system was continued and operation of the manual rod control systen was observed closely but no abnormal indications were found.

During the day shift, relay 4K2, a component analy:cd to be a possibic source of the malfunction, was removed from the manual rod control system and bench tested. Out of 400 operations, the relay failed to reset two times confirming it as the intermittently inoperable component. The relay was replaced with &

spare and the manual rod control system was returned to service.

Apparent Cause of Occurrence

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The apparent cause of this occurrence is component failure. Relay 4K2 (Rod-In Relay) intermittently failed to return to the reset position after being

.. deenergized.

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Abnormal Occurre Report No. 50-219/75-4 Pags 3 1

Analysis of Occurrence i

Since the control rod configuration caused by the event was abnormal and

, could not be handled by 'he plant core monitoring programs, estimates of the heat generation rates, peaking factor, and MCilFR were made and are as follows:

TIP Trace Using Approxi- 3-Dimensional Steady mate hbnitoring Factors State Core hbdel i Parameter  % of Parameter  % of Parameter Fuel Type Value Limit Value Limit APLilGR III-E 12.5 109% 11.83 101.7*6 III-F 12.7 10S's 12.20 102.7's I

I 10.5 94s 9.95 88.8's i LillGR III-E 14.8 89'e 14.02 85.4%

l III-F 15.0 91% 14.46 86.9%

I 12.8 77% 12.09 72.6%

Total Peaking 2.72 91.65 2.62 88.2%

Factor i

FCliFR (Type Ill-F -- --

2.79 Fuel)

Based on these results, no core thermal-hydraulic limits were exceeded that tould cause fuel damage. The average planar linear heat generation limits were, however, exceeded for approximately fourteen minutes. Under LOCA i conditions this might possibly have reduced the effectiveness of the emergency core teoling system.

Corrective Action Relay 4K2 was replaced with a new relay of the same type. Additional preventative maintenance actions for the manual rod control system will be investigated in order to prevent a recurrence of this type of malfunction, and the procedures will be reviewed to check their adequacy for this type of system failure.

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