ML19268C174

Followup to RO 79-152/01T-0:on 791118,Westinghouse Notified Util of Potential Reduction in Conservatism Re Error Allowances Assumed in Analysis for Power Range Neutron Flux High Negative Rate.Setpoints Will Be Changed

ML19268C174
Person / Time
Site:	North Anna
Issue date:	11/19/1979
From:	VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:
References
NUDOCS 8001030618
Download: ML19268C174 (1)

Text

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• 8 UE'!RO REN Virginia Electric and Pcwer Coepany J l l!T!. . M North Anna Power Station Unit il LIC. d MPF-4 Docket No. 50-338 3 [ny {g Pl2

• 4 6 24 Hcur Reportable Event Written Follow-Up Event: Possible Non-conservatism in error allowances for the ,

negative high flux rate trip protection systen as specified in the Technical Specifications.

LER/R0 79-152/01T-0 Westinghouse has infomed Vepco of a potential reduction in conser-vatism in the error allowances assumed in the analysis for the Power Range Neutron Flux High Negative Rate. The value currently listed in the Technical Specifications is 0.51 of Rated Thermal Power. This value asstred that the differentiation of the NIS power signal would eliminate all steady state errors in the circuit before the differentiation; therefore, only precision and accuracy errors after the differentiation need be considered. This asstaption is non-conservative since errors asscciated with precision

• (hysterisis, repeatability, etc.) may not be entirely eliminated by differen-t1ation. When these additional errors are factored into the analysis, a reactor trip may not occur in socie cases.

This non-conservatism was discovered by Westinghouse in a re-analysis of the flux rate error allowances.

Vepco is currently awaiting further inforsatien frte Westinghouse on this ratter. After further evaluation, technical specification and/or setpoint changes may be initiated, if necessary, to return the margin of safety in the protection syste:n.

This non-conservatism has had no effect on the plant.

The unit is currently in Mode 5 operation following refueling. The unit will remain in Mode 5 operation for the next few weeks for further maintenance.

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