05000280/LER-1979-036-01, /01T-0:on 791128,during Unit Operation,Util Notified by Engineer That Error in Current Containment Depressurization Analysis Assumed Spray Effectiveness Values Too High.Caused by Incorrect Application of Approved Model

/01T-0:on 791128,during Unit Operation,Util Notified by Engineer That Error in Current Containment Depressurization Analysis Assumed Spray Effectiveness Values Too High.Caused by Incorrect Application of Approved Model

ML18136A288
Person / Time
Site:	Surry
Issue date:	12/12/1979
From:	VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML18136A287	List: 05000280/LER-1979-036, Forwards LER 79-036/01T-0 05000280/LER-1979-036-01, /01T-0:on 791128,during Unit Operation,Util Notified by Engineer That Error in Current Containment Depressurization Analysis Assumed Spray Effectiveness Values Too High.Caused by Incorrect Application of Approved Model
References
LER-79-036-01T, LER-79-36-1T, NUDOCS 7912140394
Download: ML18136A288 (2)

LER-1979-036, /01T-0:on 791128,during Unit Operation,Util Notified by Engineer That Error in Current Containment Depressurization Analysis Assumed Spray Effectiveness Values Too High.Caused by Incorrect Application of Approved Model

Event date:
Report date:
2801979036R01 - NRC Website

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I During unit operation, on November 27, 1979, Vepco was notified by the architect-

[]:]}] I engineer of an error in the current containment depressurization analysis for Surry [Q]}] !Unit 1.

Specifically, the spray effectiveness values assumed for the containment

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I spray systems were higher than can conservatively be expected.

Revised analyses

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44 47 o:::I]J JThe error was caused by the architect-engineer's incorrect application of an approved OJJJ 1spray effectiveness model.

As a result, the spray effectiveness assumed in perfor-o:II] 1ming the containment depressurization analysis was erroneously high.

More restrictive o:::I)) llimiting conditions for unit operation have been imposed based on corrected analysis.

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LER 79-036-0lT-0 Surry Unit 1 Docket No. 50-280

Description of Event

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Attachment Page 1 On November 27, 1979, Vepco was notified by the architect-engineer, Stone and Webster, that an error has been identified in the current con-taimnent depressurization analysis for Unit No. 1.

Specifically, spray effectiveness values had been assumed for the containment spray systems which were higher than can be conservatively expected.

Probable Consequences Reanalysis, using conservative values for spray effectiveness, indicate that for the worst case LOCA, assuming the most detrimental extremes of initial plant operating conditions, the containment depressurization criteria might not have been met.

That is, while the containment would have been restored to subatmospheric conditions within one hour, the third pressure peak occurring after the first hour could have caused the containment pressure to return slightly positive (approximately 0.5 psi) for approximately 1.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />.

This would have resulted in a slight increase in offsite dose over the original estimate.

Cause of Occurrence Following the completion of interim modifications to ensure adequate NPSH to the Low Head Safety Injection and Outside Recirculation Spray pumps, contaimnent depressurization analyses were performed which established limiting conditions for operation.

The spray effectiveness values used for the contain-ment depressurization analyses were developed using an approved model.

However, the architect-engineer has now determined that the spray effectiveness model was inappropriately applied yielding an erroneously high value.

Corrective Actions

Contairnnent depressurization analyses, using conservative values for spray effectiveness have been performed to establish revised limiting conditions for operation.

The revised limits are slightly more restrictive than those ori-ginally established.

Operation of Surry Unit 1 is in accordance with the revised operating limits.

The current limiting conditions for Surry Unit 2 are similarly affected.

However, since the final modifications to address NPSH concerns are currently in progress on Unit 2, that unit will return to operation under a different revised set of LC0 9s.