ML19211D271

LER 79-132/01T-0:on 791231,during Review of Effects of Changing RCS Cold Leg Temp on Accuracy of Power Range Nuclear Instrumentation,Calibr Procedures Found Inconsistent W/Accident Analysis.Caused by Procedure Error

ML19211D271
Person / Time
Site:	Davis Besse
Issue date:	01/11/1980
From:	Lingenfelter T TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19211D270	List: ML19211D269 ML19211D271
References
LER-79-132-01T, LER-79-132-1T, NUDOCS 8001170391
Download: ML19211D271 (3)

Text

NHC FORM 3GG U. S. NUCLEAR REGULATORY COMMISSION (7 77)

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(PLEASE PRINT OR TYPE ALL REQUIREO INFORMATIoN)

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63 61 Cd b3 74 75 REPORT DATE 80 DOCK E T N U'.'B E R EVENT DATE EVENT OESCAIPTION AND PRO 9ABLE CONSEQUENCES h  !

o 2 l During a review of Jhr 'ffects of a changing Reactor Coolant System (RCS) cold leg l o 3 i temperature on the accuracy of the power range nuclear instrumentation (UI), the pro- l o ,, l ceduresgoverning NI calibration were found to be inconsistent with the assumptions of l o s l the accident analysis. This could result, during a cooldown transient, in a high flux l o 6 l reactor trip at 114% actual power instead of the 112% power as assumed in the accidenti io 7 l analysis. Preliminary evaluation of a cooldown transient with the additional 2% error l o s I shows no significent change in the event. (NP-32-79-15) l coo'E '^"$E CO St ei$$e COMPONENT CODE St,8C DE S E lo 9 lI l A l@ yh l Zlh lI N l S l T l R l U lh lI l@ l Zl h 7 8 9 to 11 12 13 19 19 M

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42 43 44 4; CAUSE DESCRIPTION A*JO CORRECTIVE ACTIONS h i ii o l The cause of this occurrence was a procedure error. The RCS daily heat balance check j

,i i l allowed a normal dif ference between NI indicated power and the heat balance power of I

,, ., l up to 2% in the non-conservative direction. The procedure has been modified to assure l

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TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-32-79-15 DATE OF EVENT: December 31, 1979 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURREHCE: Power range nuclear instruments calibration defici-ency Conditions Prior to Occurrence: The unit was in Mode 5, with Power (MRT) = 0, and Load (Gross MWE) = 0.

Description of Occurrence: During a review of the effects of a changing Reactor Coolant System (RCS) cold leg temperature on the accuracy of the power range nuclear instrumentation (NI), the procedures governing NI calibration were found to be incon-sistent with the assumptions of the Final Safety Analysis Report (FSAR).

The specific effect under investigation'was the decrease in NI indicated power below actual reactor power with a decrease in RCS cold leg temperature. The decrease in NI indicated pot-:cr is caused by a re' duction in neutron leakage from the reactor vessel as cold leg temperature falls and the density of water in the vessel down-comer increases (along with the concentration of boron atoms per unit volume).

A review of the safety analysis for those accidents involving an overcooling tran-sient with a reactor trip on high flux revealed that for the feedwater temperature reduction from 100% full power, the error induced in NI power was approximately 4%

between NI power and heat balance power. This analysis also assumes that indicated NI power is equal to (or greater than) the heat balance power. However, the station procedures allow the heat balance power to be 2% greater than the indicated power.

In the event of an excessive heat removal transient from 100% full power, this addi-tional 2% error could cause the reactor to trip at 114% power instead of the 1121 assumed in the FSAF..

Designation of Apparent Cause of Occurrence: The procedures covering the calibration requirments were in error. These procedures were written in accordance with instruc-tions provided by Babcock and Wilcox.

Analysis of Occurrence: There was no danger to the health and safety of the public or to s tation personnel. Preliminary evaluation of a feedwater temperature reduc-tion transier : with a 2% error between NI power and heat balance power shows that there are no significant -hanges in the outcome of the event. No such feedwater -

temperature reduction transients have occurred. , ,

176L2 24i Corrective Action: The RCS Daily Heat Balance Check, ST 5030.01, has been modified with concurrence from Babcock and Wilcox to assure that the NI power is maintained equal to or greater than the heat balance power. This will assure that in the event LER #79-132

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TOLEDO EDISON COMPANY - '

DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-32-79-15 of an excessive heat removal transient, that the reactor will be tripped at 112%

power or less.

Failure Data: There have been no previous similar reportable occurrences.

LER #79-132 e

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f762 242 .