ML20210D696

Informs of Results of Cycle 3 Startup Physics Tests Conducted Using Method Described in, Rod Bank Worth Measurement Utilizing Bank Exchange. Ref Bank,Shutdown C, Worth Measured 14% Below Predicted Value

ML20210D696
Person / Time
Site:	Mcguire
Issue date:	09/15/1986
From:	Tucker H DUKE POWER CO.
To:	Harold Denton, Youngblood B Office of Nuclear Reactor Regulation
References
TAC-62972, TAC-62981, TAC-62982, NUDOCS 8609190300
Download: ML20210D696 (4)

Text

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Duxn POWER GOMPANY P.O. Box 03189 Ott ARLOTTE, N.C. 28242 "O ".;.". -it".

MC' September 15, 1986 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Consnission Washington, D.C. 20555 ATTENTION: Mr. B.J. Youngblood, Project Director PWR Project Directorate #4

Subject:

McGuire Nuclear Station, Unit 2 Docket Nos. 50-370

Dear Mr. Denton:

During the Cycle 3 startup physics tests perfonned at McGuire Unit 2, rod worths were measured using the method described in " Rod Bank Worth Measurement Utilizing Bank Exchange", (WCAP-9863-A). This test process incorporates a two tiered set of criteria for test result evaluation. These are " review" criteria, which have no direct safety significance, and " acceptance" criteria, which is based on meeting safety analysis input assumptions. The specific lists of these criteria are defined in WCAP-9863-A, Section 5.0 and also listed in the NRC Safety Evaluation Report (SER). The SER also requires that, in the event that a review or accep-tance criterion has not been met, a report be submitted to the NRC.

On June 26, 1986, during the McGuire Unit 2 Cycle 3 Rod Exchange test, the ref-erence bank Shutdown C, worth was measured to be 14.5% below the predicted value.

'This deviation exceeded review criterion (1) on the reference bank worth of 10%.

' All other measurements met their review criteria. All rod exchange acceptance criteria were met. Therefore, no safety analysis input assumptions are affected.

The attached report summarizes review criteria evaluations as directed in the NRC SER.

8609190300 86071S yDR ADOCK 05000370 i

PDR A R 00I L

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1 Mr. Harold R. Denton J

. September 15, 1986 i Page 2 'l I

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. If there are any questions regarding this report, please contact Duke through the.  !

norwal licensing channels.

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' Very truly yours,

'l C/d.d /$-

Hal B. Tucker

.RLG/105/jgm Attachments xc: W.T. Orders NRC Resident Inspector McGuire Nuclear Station Darl Hood, Project Manager '

Division of Licensing U.S. Nuclear Regulatory Comission Washington, D.C. 20555

ATTACHMENT McGuire Unit 2 Cycle 3 ' Rod Exchange Test -

Summary of Review Criteria Evaluation INTRODUCTION / BACKGROUND Duririg the Cycle 3 stattup physics teste performed at McGuire Unit 2, rod worths

.were measrured using the method. described in " Rod Bank Worth' Measurement Utilizing Bank Exchange", (WCAP-9863-A). This test process incorporates a two tiered set of criteria for test reault evaluation. These are " review" criteria, which have no direct safety significance, and " acceptance" criteria, which are based on meeting safety analysis input assumptions. The specific lista of these criteria are defined in WCAP-3863<-A, Section 5.0 and also listed in the NRC Safety Evaluation Report (SER).as attached in Appendix A.

On June 26, 1986, during the McGuire Unit 2 Cycle 3 Rod Exchange test, the reference bank, Control Bank C, worth was measured to be 14.5% below the predicted value. This deviaticn exceeded review criterion (1) on the reference bank vorth of 10%. All other maasurements met their review criteria. All rod exchange ecceptance criteria were set. Therefore, no safety analysis input assumptions are

'affacted. .This report autsmarizes review criteria evaluations as directed in the NRC SER.

EVALUATION The evaluation cente:ed on.the following areas:

1) Review of analytical predictions

2) Review of reactivity computer traces and assumptions.

The models und calculatiens on which the predictions were based were reviewed. No errors were Cound and all quality assurance requirements were met.

The delayed neutron fraction (B,) can be affected by rodded configurations by as much as 3% in some cores. For AcGuire 2 Cycle 3, the effect is small (0.4%).

Increases in B can also be obtained from refined B calculations. Work by 3

L R.J. Tuttle (17 results in a 2% increase in the delayed neutron fraction. The use l of Tuttle's method, reconsended in Reference 2, was intended. However, a i

mirunderstanding about the code used to generate delayed neutron data resulted in j the ase. of the standard Westinghouse method. For McGuire, a 2.4% increase in measured reactivity of Control Bank C would have resulted from utilizing Tuttle's

}: Method and redded B's.

In reviewing the reactivity trace from the recorder strip chart for the

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measurement of Control Bank C, the trace was found to contain no noticeable anomalies. Although the change from unrodded to the Control Bank C In condition results in a radial redigitribution into the peripheral assemblies, this was not observed in the trace. Specifically, the predicted radial power redistribution caused by Control Bank C insertion would result in reactivity "undershoot"

following the rod motion. This spatial effect is typical in rod worth reactivity traces and would normally be accounted for in the trace analysis. However, no spatial effects were visible in this trace. This apparent absence of a spatial redistribution effect could have contributed to the lower measurement of Control Bank C rod worth.

CONCLUSIONS Westinghouse has reviewed the results of the McGuire 2 Cycle 3 Rod Exchange test and has found no deficiency in either the calculational models used for prediction or the rod worth measurement and procedures. The likely cause of the measured versus predicted differences in reference bank reactivity is a combination of small variances in input to the reactivity computer and measurement environment effects. There is no effect on the safety analysis input assumptions due to these measurements.

REFERENCES (1) R.J. Tuttle, " Delayed-Neutron Data for Reactor-Physics Analysis", Nuclear Science and Engineering, Volume 55, pages 37-71,1975.

(2) Letter 85DA*-G-083 McGuire Nuclear Station Unit 1 Cycle 3 Rod Swap Measurement Discrepancies.

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