ML18116A383

LER 79-022/01X-1 on 790621:increase in Steam Generator Ref Leg Temp Resulting in Rise in Containment Temp Not Accounted for by Westinghouse Accident analysis.Long-term Action Under Evaluation

ML18116A383
Person / Time
Site:	Surry
Issue date:	08/10/1979
From:	Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML18116A382	List: ML18116A381 ML18116A383
References
LER-79-022-01X, LER-79-22-1X, NUDOCS 7908200376
Download: ML18116A383 (3)

Text

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION (7-7J)

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[}:II] I On 6/21/79 Westinghouse notified VEPCO of a non-conservatism in the accident analysis.I ITTIJ Specifically, the increase in steam generator reference leg temperature resultant

[QJIJ from a rise in containment temperature was not properly accounted for. Consequently,

[QTIJ safeguards actuation may be delayed after a high energy line break. This event is

[QTIJ reportable as per Technical Specifications 6.6.2.a.8.

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The event was caused by a deficiency in the accident analysis. Immediate corrective I action has been completed and long term action is being evaluated.by Westinghouse andl

[J]J] VEPCO. Westlnghouse has submitted a 10 CFR 21 report.

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• UPDATE REPORT Attachment, page 1 of 2 Surry Power Station, Unit 1

! Docket No: 50-280 Report No: 79-022/0lX-l Event Date: 06/21/79 Title of Report: Non-Conservatism in Accident Analysis

1. Description of Event:

On 6/21/79, Westinghouse notified VEPCO of a non-conservatism in the analysis. Specifically, the potential increase in the steam generator reference leg resultant from a rise in containment temperature was not properly accounted for in the analysis. The increased reference leg water temperature will result in a decrease of the water column density which gives an apparent increase in steam generator level. This event is reportable as per Technical Specifications 6.6.2.a.8.

2. Probable Consequences and Status of. Redundant Systems:*

This potential level bias could result in delayed protection signals which are based on low-low steam generator water level. Backup signals were available from the Overtemperature Delta T, pressurizer pressure, contain-ment pressure and safety injection systems.

3. Cause:

This event was caused by the identification of a deficiency in the accident analysis for High Energy Line Break.

4. Immediate Corrective Action:

Westinghouse prepared and submitted a 10 CFR 21 Review report. Westinghouse and VEPCO are evaluating corrective action at this time.

As a result of this evaluation, it has been determined that an increase of ten percent (10%) in the low-low steam generator level trip setpoint would compensate for the temperature effect on the reference leg.

Technical Specification 2.3.A.3.b directs that the low low steam generator level trip be set at> 5% of narrow range instrument span. The trip set-point has been increased by the recommended 10% plus 2% for instrument error on Unit 1. Technical Specifications will not need to be changed at the present time. Pending an alternative long term solution, 15%

will be used as the minimum allowable safety instrument setting.

Attachment, page 2 of 2 Surry Power Station, Unit 1 Docket No: 50-280 Report No: 79-022/0lX-O Event Date: 06/21/79 Title of Report: Non-Cbnserva tism in Accident Analysis

5. Subsequent Corrective Action: I I

Several possible long term corrective actions are under evaluation. Once these studies are completed, they will be analyzed and if one is determined viable, it will be implemented. If changes to Technical Specifications are required, they will be made at that time.

6. Actions Taken to Prevent Recurrence:

The proposed corrective actions will prevent recurrence.

7. Generic Implications:

This error may be generic to Westinghouse PWR's.