05000338/LER-1980-055-01, /01T-0:on 800626,review of FSAR Safety Analyses for Boron Dilution Accidents Determined That Nonconservative RCS Vols Were Used for Cold Shutdown Condition.Cause Undetermined.Solution Pending Further Evaluation

/01T-0:on 800626,review of FSAR Safety Analyses for Boron Dilution Accidents Determined That Nonconservative RCS Vols Were Used for Cold Shutdown Condition.Cause Undetermined.Solution Pending Further Evaluation

ML19320C079
Person / Time
Site:	North Anna
Issue date:	07/10/1980
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19320C077	List: 05000338/LER-1980-055, Forwards LER 80-055/01T-0 05000338/LER-1980-055-01, /01T-0:on 800626,review of FSAR Safety Analyses for Boron Dilution Accidents Determined That Nonconservative RCS Vols Were Used for Cold Shutdown Condition.Cause Undetermined.Solution Pending Further Evaluation
References
LER-80-055-01T, LER-80-55-1T, NUDOCS 8007150777
Download: ML19320C079 (3)

LER-1980-055, /01T-0:on 800626,review of FSAR Safety Analyses for Boron Dilution Accidents Determined That Nonconservative RCS Vols Were Used for Cold Shutdown Condition.Cause Undetermined.Solution Pending Further Evaluation

Event date:
Report date:
3381980055R01 - NRC Website

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Q" U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT CONTROL BLOCK / / / / / / / (1)

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DOCKET NUMBER EVENT DATE REPORT DATE EVENT DESCRIPTION AND PROBABLE CONSEQUENCES (10)

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During a review'of the FSAR safety analyse.s for boron dilution accidents, it

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was determined ; hat nonconservative RCS volumes were used for the Cold Shut-

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down conditiori..Since the FSAR analysis assumes a full RCS and the RCS may

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be drained to the centerline of the RCS hotlegs, the volumes used in the

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analysis are nonconservative. This event is reportable pursuant to T.S.

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6.9.1.8.h.

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public health and safety are not affected.

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The cause of the discrepancy is not known. A minimum of two shutdown banks

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will be fully withdrawn and available for trip during shutdown conditions.

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withdrawn banks, the operator will 'nitiate boration immediately. This

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solution will be used pending further evaluation.

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80 0.715 0 M NAME ~ OF PREPARER -

W. R. CARTWRIGHT PHONE (703) 894-5151

4.

I Virginia Electric and Power Company North Anna Power Station, Unit 1 Attachment: Page 1 of 2 l

Docket No. 50-338 Report No. LER 80-055/01T-0

Description of Event

During a review of the FSAR safety analyses for boron dilution accidents, it was determined that nonconcervative RCS volumes were used for the Cold Shutdown condition. FSAR section 15.2.4.3 states that in the Cold Shutdown condition with a boron concentration of 1500 ppm, all RCC assemblies in, and a dilution flow rate of 300 gpm, the reactor could go critical in 15.5 minutes. This result may not be conservative because the RCS was assumed to be full.

In the Cold Shutdown condition the RCS may be drained to the centerline of the RCS hotlegs for main-tenance. This event applies to both Unit 1 and 2 and is reportable pursuant to T.S. 6.9.1.8.h.

At the time the event was determined to be reportable Unit I was in Mode 1 (Power Operation) and Unit 2 was in Mode 3 (Hot Standby).

Probable Consequences of Occurrence Since in Modes 3, 4, 5 and 6, the PG valves to the blend system are locked closed within 15 minutes after a planned dilution or makeup activity pursuant to T.S. 3.1.1.3.2 and neither unit is in cold shutdown, there are no immediate consequences which will affect the public health and safety. Westinghouse is performing a review of the safety signifi-cance of an inadvertant boron dilution at shutdown conditions and has identified the following potential concerns:

1)

There may be insufficient indication of an inadvertant dilution event to assure timely action by the operator prior to a

' return to critical.

2)

Without positive operator action, the potential exists for system overpressurization and limited fuel damage.

Both Vepco and Westinghouse are continuing investigations of the safety significance of inadvertant boron dilution at shutdown conditions.

Cause of Event

The cause of the discrepancy in FSAR analyses for boron dilution accidents is not known.

Immediate Corrective Action

In order to increase the safety margin for boron dilution accidents the following interim actions have been implemented:

1)

During shutdown conditions and while on the residual heat removal system, a minimum of two shutdown banks will be avail-able for trip (fully withdrawn) whenever dilution /bocation capability exists.

Attachment: Page 2 of 2 2)

Following either a source range high flux at shutdown alarm or trip of the withdrawn bank, the operator will terminate the dilution and f attiate boration immediately.

3)

The source range detectors and high flux at shutdown alarm will be verified as operable during shutdown.

The above interim action will continue until investigation results indicate other actions to be appropriate.

Scheduled Corrective Actions Corrective actions other than the actions listed above are pending the results of investigations of the safety significance of inadvertant boron dilution at shutdown conditions.

Actions to Prevent Recurrance No actions to prevent recurrance are required.

Generic Implications Westinghouse is conducting an investigation of the safety signifi-cance of inadvertant boron dilution at shutdown conditions for generic implications.