05000336/LER-1985-001, :on 850123,safety Analysis Error Found.Caused by Inconsistency Between Tech Spec Requirement on Axial Shape Index & Safety Analysis Assumptions on Index Used as Input to Small Break LOCA Analysis

:on 850123,safety Analysis Error Found.Caused by Inconsistency Between Tech Spec Requirement on Axial Shape Index & Safety Analysis Assumptions on Index Used as Input to Small Break LOCA Analysis

ML20107H963
Person / Time
Site:	Millstone
Issue date:	02/20/1985
From:	Mroczka E, John Parillo NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF ADMINISTRATION (ADM)
References
LER-85-001, LER-85-1, MP-6660, NUDOCS 8502270336
Download: ML20107H963 (4)

LER-1985-001, on 850123,safety Analysis Error Found.Caused by Inconsistency Between Tech Spec Requirement on Axial Shape Index & Safety Analysis Assumptions on Index Used as Input to Small Break LOCA Analysis

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)
3361985001R00 - NRC Website

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An inconsistency was found between the Technical Specification requirement on Axial Shape Index (ASI) and the safety analysis assumptions on ASI that are input to the Millstone 2 Small Break Loss of Coolant (LOCA) analysis. The Unit 2 Small Break LOCA analysis was performed by Combustion Engineering. The event was declared immediately reportable by site procedures and falls under the 30 day reportable criteria of 50.73 (a), (2) V & V1.

The ASI inconsistency between Technical Specifications and Safety Analysis could have allowed plant operation in an unanalyzed region should a small break LOCA occur. Administrative controls were immediately implemented to preclude any unan-alyzed operation until further corrective actions could be implemented.

Reanalysis has shown that when the correct ASI inputs are used in the small break LOCA model, Peak Clad Temperatures (PCT) increase from 1971 degrees F to 2035 degrees F, still within the 2200 degrees F 10CFR50.46 LOCA limits on PCT.

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EMPIRES 8/31/86 FACILITY esaast pl DOCKET NUteBER (23 LER NUMef R 163 PAGE (3) vtan SE Qus =T.a t atveosu Millstone Point Unit 2 0 l5 l0 j o lo l3 l 3 l6 8l 5

-- O l0l1 0 l0 0l2 OF 0 l3 rExt c-M wmRes mww nn The Safety Analysis that supports Millstone 2 operation is in part supplied by Combustion Engineering (C-E).

During the investigation phase of a potential Techni-cal Specification change, C-E identified an inconsistency between the Millstone 2 Technical Specification Axial Shape Index (ASI) values and the ASI assumptions utilized in the small break Loss of Coolant analyses performed by C-E.

The most negative Axial Shape Index (ASI) input to the LOCA analysis was an ASI of

.14.

Plant Technical Specifications allow a 100% power ASI of no more negati,ve than

.10.

Considering the

.06 ASI uncertainty assumed in the analysis, the plant could conceiv' ably operate with an ASI of (.10) - (.06) =

.16.

This is not bounded by the

.14 ASI input to the small break LOCA model.

The error was reported on 1/23/85 and was declared an immediate report to the NRC and state by site procedures. Administrative controls at this time were put in place to preclude plant operation in the unanalyzed ASI region, until corrective actions could be taken. Subsequently, a calculation was performed to determine the effects on the small break LOCA of the more negative ASI value of

.16.

The Peak Clad Temperature (PCT) during a postulated small break LOCA increased from 1971 degrees F to 2035 degrees F as a result of the mere negative ASI of

.16.

This increase still does not exceed the 10CFR50.46 limit for PCT, which is 2200 degrees F.

With this reanalysis in place and QA verified, administrative controls were removed on plant operation.

This incident was declared a 30 day report based on 100FR50.73 (a)(2)(V) and (VI).

This is because the ASI inconsistency could have allowed plant operation in unan-alyzed ASI space, where the ability of plant safety systems to mitigate a small break LOCA were not analyzed.

This error was in place since Cycle 3 (1979). This was the last time a Technical Specification change to the ASI Limiting Condition for Operation (LCO) was issued.

Three mitigating factors must be considered concerning this safety analysis incon-sistency:

1)

Actual plant operation in the unanalyzed ASI space during the time the error was in place, is extremely remote. Operation in the unanalyzed ASI space would indicate a severe abnormality in core power distribution.

2)

The only way operation in the unanalyzed ASI space could occur is if the ASI uncertainty of

.06 assumed in the analysis was at or near the negative ASI uncertainty limit of

.06.

3)

Even if operation did occur in the unanalyzed ASI space, reanalysis shows that plant safety systems were adequate to maintain PCT during a postulated small break LOCA to 2035 degrees F, below the 2200 degreor F 10CFR limit.

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,,,,c,,,,,,,,, t,T, This inconsistency between Technical Specification ASI limits and Safety Analysis limits on ASI is not common to any other Millstone 2 safety analysis transient nor is it a generic problem applicable to any other nuclear unit.

In summary, the corrective actions were to perform an analysis to ensure that plant h

operation with current Technical Specifications meet all LOCA acceptance criteria.

This analysis is complete.

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February 20, 1985 MP-6660 U. S. Nuclear Regulatory Commission Documept Control Desk Washington, D. C. 20555

Reference:

Facility Operating License No. DPR-65 Docket No. 50-336 Reportable 9ccurrence RO 50-336/85-001-0 j

Gentlemen:

This letter forwards the Licer. oe Event Report 85-001-0 required to be submitted within thirty (30) dafs pursuant to paragraph 50.73 (a) (2)

(V) and (VI).

Yours truly, NORTHEAST NUCLEAR ENERGY COMPANY D/

E. J. Mroczka Station Superintendent Millstone Nuclear Power Station EJM/JJP:mo

Attachment:

LER RO 50-336/85-001-0 cc:

Dr. T. E. Murley, Region I jh h

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