ML19241A752

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Deficiency Rept:Present Rod Controller Is Less Conservative than Assumed in Safety Analysis & Could Lead to DNB Reduction Below Min Design Value.Revised Setpoint Will Be Included in Tech Specs
ML19241A752
Person / Time
Site: Mcguire, McGuire  Duke Energy icon.png
Issue date: 06/22/1979
From:
DUKE POWER CO.
To:
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19241A743 List:
References
SD-369-79-03, SD-369-79-3, SD-370-79-04, SD-370-79-4, NUDOCS 7907090353
Download: ML19241A752 (1)


Text

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Reoort 50.. SD-369/79-03, 370/79-04 Rep rir t Date: June L.. 1979 Facility: McGuire Suelear Station - Units 1 and 2 Identification of Defluiencv: Dropped Rod Analysis Deficienc Description of Deficiency:

Westinghouse Electric Corporation informed Duke that the existing rO contro 'er may estimate a core average power level less than actual during certain caJ area events. Also, conservatism is reduced by inconsistencies between rod control settings actually used in the equipment and those assumed in the safety analysis.

In the event of a single dropped rod, the automatic red control system responis te the indicated consequent power reduction by withdrawing control rods ta restore the steady state power level. If the instrumentation orovides a low estimate of the core-wide power level, then the control system could respcnd to produce a power overshoot. The potential resulting power iver3htot coule result in calculated violation of the plant DNB limit.

A second reduction in conservatism arises because the safety anal fsis for the single rod drop event utilized non-conservative controller input settings which have an impact on the ability of the rod control system to minimize power overshoot and, hence, maxitaize DNB margins. The use of noncenserva-tively low values for these settings resulted in an FSAR analysis which ,

underestimated the resulting potential power overshoot. '

Additional details of the deficiency are descrioed in a March 37, 1979 letter, SS-TMA-2063, to Mr. John G. Davis, NRC/01E, from Mr. T. M. Anderson. Westinehouse Analysis of Safety Imolications:

Worst case safety consequences would be a reductica in DNBR below the minimum design value.

Corrective Action:

In a meeting between representatives of the NRC Staff and Westinghouse Electric Company on April 12, 1979, a change to the setpoint of the high flux rate trip in the reactor prctection system was discussed. In that meeting it was agreed that lowering (making more restrictive) the high negative rate flux trip would orovide adequate protection for any postulated rod drop accident.

Accordingly, this revised setpoint will be included in the tecanical speci-ricaticas issued with each unit's operating license.

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