05000338/LER-1979-085-03, /03L-0 on 790715:following Power Reduction Caused by Secondary Plant Problems,Quadrant Power Tilt Alarm Was Observed.Possibly Caused by Dropped Rodlets.Tilts Under Review

/03L-0 on 790715:following Power Reduction Caused by Secondary Plant Problems,Quadrant Power Tilt Alarm Was Observed.Possibly Caused by Dropped Rodlets.Tilts Under Review

ML19207B326
Person / Time
Site:	North Anna
Issue date:	08/20/1979
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19207B325	List: 05000338/LER-1979-085, Forwards LER 79-085/03L-0 05000338/LER-1979-085-03, /03L-0 on 790715:following Power Reduction Caused by Secondary Plant Problems,Quadrant Power Tilt Alarm Was Observed.Possibly Caused by Dropped Rodlets.Tilts Under Review
References
LER-79-085-03L, LER-79-85-3L, NUDOCS 7908240427
Download: ML19207B326 (3)

LER-1979-085, /03L-0 on 790715:following Power Reduction Caused by Secondary Plant Problems,Quadrant Power Tilt Alarm Was Observed.Possibly Caused by Dropped Rodlets.Tilts Under Review

Event date:
Report date:
3381979085R03 - NRC Website

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EVENT DESCR PTION A DPROBA LEC JENCES [o p j l On 7/15/79 at about 0548 fol'owing a power reduct ion canSmLhy socondary Plant I

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Subsecuent t il t calculations l

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This event is reportable pursuant to T.S. 6.9.1.9.b.

The health and I

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l LER/R0 79-079/03L-0. This problem is currently being investigated bv both Venco I

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Core flux napping surveillance has been increased, however suf ficient inforcation has not been obtained to deter-ine the exac t cause.

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Attachment:

Page 1 of 2 North Anna power Station, Unit #1 Docket No.: 50-338 Report No.: LER 79-035/03L-0 Description cf Event :

On 7/15/79 at approximately 0548 during a Power Escalation following mainte-nance on a secondary plant feedwater pump and main condenser, the alarn on core tilt deviation was observed.

Seven periodic tests which evaluate the tilt utilizing excore detector currents were perforced.

The tilt peaked in the upper half of the core with a tilt ratio of 1.0561 at 0652 and the ala.m cleared when the tilt ratio decreased to 1.0178 at 0920.

The action statements of T.S. 3.2.4 were followed until the tilt reduced belcw the 1.02 limit.

Probable Consequences of Occurrence The limit of T.S.

1.02 provides for DNB and linear heat generation rate pro-tection of X-Y plane power tilts. A period of two hours of operation between 1.02 and 1.09 is allowed by Technical Specifications to allow for problen analysis and correction.

A power reduction from 100% is necessary to reinstate the nargin of uncertainty for FQ.

Since the reactor was at reduced power during this event, the health and safety of the general public were not affected.

Cause of Concurrence An evaluation of potential causes of the tilt condition has been performed.

P~eliminary results from the evaluation ruled out control rod misalignment, L :rnable poison rod failure, 1-Salance of loop thermal power, fuel enrichment variations, and calculational errors as being the cause of the tilt condition.

The possibility of dropped RCCA rodlets has not been ruled out.

Therefore, a detailed safety evaluation to assess continued operation with a few dropped RCCA rodlets was performed.

The results of this safety evaluation conclude that there will be no adverse impact on safety fron continued operation with the current Technical Specifications limit.

Specifically, shutdown nargin is adequate, achievable power distribution during the remainder of NA1, Cycle 1 operation is bounded by the power distribution assumed in the FSAR, and the presence of dropped RCCA rodlets will not result in an inoperable control rod.

These results have been discussed with the NRC Division of Nuclear Reactor Regulation.

Inmediate Corrective Action Af ter the presence of the tilt was noted, the actions required by T.S.

3.2.4 were followed.

Since the power level was approximately 50% no further power reduction was required to restore the margin of safe ty for F.Q. and since the duration of the tilt condition was less than 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />, no Power Rangu neutron flux-high trip setpoint reduction was required.

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Page 2 of 2 Scheduled Corrective Action To continue to perforn more frequent flux napping (i.e., bi-weekly whenever core conditions pernit) as well as acquire and analyze relevant data obtained during ona-,tions which result in an increased tilt.

To conduct a visual exaninatic -

the core to determine the condition of the control rods.

Actions Taken To Prevent Recurrence No specific actions have been outlined.

However, the tilts are being reviewed on a case-by-case basis in an attempt to prescribe an operating technique which would reduce the nagnitude and frequency of tilt occurrences.

As a result of more detailed evaluation and core inspection, additional actions may be taken.

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