ML20059J238

Safety Evaluation Accepting 921125 TS Changes,Augmented by 930702 Response to NRC Rai,Allowing Use of Fixed Incore Detector Sys at Facility

ML20059J238
Person / Time
Site:	Seabrook
Issue date:	11/05/1993
From:	Office of Nuclear Reactor Regulation
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References
NUDOCS 9311120108
Download: ML20059J238 (6)

Text

[p r<cg[$ UNITED STATES NUCLEAR REGULATORY COMMISSION i 't g M(

j i S[ WASHINGTON, D.C. 20555-0001

, . ENCLOSURE 1 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO SEABROOK STATION UNIT 1 i FIXED INCORE DETECTOR SYSTEM

1.0 INTRODUCTION

In a letter of November 25, 1992 (Ref. 1), North Atlantic Energy Service Corporation requested U.S. Nuclear Regulation Commission (NRC) review of (Ref. 2) YAEC-1855P, "Seabrook Station Unit 1 Fixed Incore Detector System Analysis." This submittal was '

augmented by a July 2, 1993 (Ref. 3) response to an NRC request for additional information. Seabrook Station contains two complete and independent incore detector systems. The first is a ,

movable incore detector system, which uses movable fission chambers as designed by Westinghouse. The second detector system employs self-powered fixed detectors. The Fixed Incore Detection System provides information on the gamma and neutron flux levels in the same 58 instrumented assembly locations within the reactor core as the movable system. The signal produced from the i platinum incore is combined with analytical predictions of neutron flux to estimate the incore three-dimension power distribution. This power distribution is then used to derive the maximum local power peak and hot channel factor which are used to establish limits using a method similar to the one used with the movable Lncore Detector System. A detailed description of the Fixed Incore Detector System is given in Section 2.0 of YAEC- l 1855P. l l

j The purpose of the analysis provided in YAEC-1855P is to demonstrate that the Fixed Incore Detector System is comparable in accuracy and functionality to the movable Incore Detector l

System and to define the uncertainty for these power distribution measurements. It is the licensee's intention to use the fixed i i

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2 incore detector system as the primary power distribution measurement system with the movable incore detector system serving as a backup.

2.0 EVALUATION The previously approved CASMO-3/ SIMULATE-3 code package is used  !

as the analytical method for the prediction of neutron detector i

signals and three dimensional power distributions. This code system was modified to produce analytical predictions of gamma  ;

sensitive detector signals on a core wide basis. The gamma <

response calculation for platinum detectors within the SIMULATE-3 code is similar to the method used for standard fixed detector type calculations originally developed and demonstrated for rhodium detectors. The total signal given by platinum incore i detectors is a function of both the incident gamma and neutron flux. The gamma portion of the detector signals is determined by detailed response and gamma flux calculations. The neutron component is first determined on a core average basis and is then distributed by a weighting function of thermal neutron flux at each detector location. The average signal contribution due to neutrons was determined from operational data and public domain studies and was not the subject of a rigorous testing program.

1 The methods and calculations described in YAEC-1855P were applied to more than twenty power distribution measurements taken during 1 Cycle 1 and 2 operation at Seabrook Station. An uncertainty analysis was performed on this data which showed uncertainties of 4.13% for Fdh and 5.21% for Fxy and Fq. These uncertainties are f specific to the analytical physics methods, CASMO-3/ SIMULATE-3 used at Yankee, the incore data processing code, FINC, and the platinum fixed detectors currently in use at Seabrook Station.  !

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3.0 CONCLUSION

Based on our review of YAEC-18559, we have found the methods '

employed by Yankee Atomic to convert the platinum detector signals to power distribution are mathematically accurate and '

reasonable from an engineering standpoint. In addition, the -

uncertainty analysis performed on the data collected during Cycles 1 and 2 indicates that the Fixed Incore System is comparable in accuracy to the Standard Movable Incore Detector System. However, for the following reasons, the NRC. finds that both systems should be used until additional benchmark data can  !

be obtained:

1. There is a burnup dependence in the fixed / movable inferred measured Fry and Fq. The licensee responded to this concern by showing that the difference was most likely due to the inherent differences in the reactor physics methods used to predict the power distribution. While this may in fact be l true, it i- important that the ratio be monitored in future cycles to masure that the two methods do not continue to diverge which would indicate a problem with one of the systems.

2. The fraction of the total signal which is due to neutrons is approximate. It is not a well known number and is not based on control experiments. It is important that more core burnup be achieved to ensure that this ratio does not change significantly with core life.

3. There is little experience with a fixed platinum detector system in this country. This is the first plant to be approved to use this system for Technical Specification surveillance, and this is the fir t Westinghouse plant to employ a fixed incore detector system to determine core

4 i peaking factors.

i For these reasons, the following condition will be placed on the use of the platinum fixed incore detector system at Seabrook Station.

For the remainder of the current Cycle 03 operation, the licensee shall acquire one additional core flux map with the movable incore detector system, within the burnup window of EOL as defined in the Cycle 03 Nuclear Design Report. Eleven Cycle 03 ,

core flux maps have been taken to date with the movable incore detector system.

During Cycle 04 operation, the licensee shall acquire additional core flux map data from the movable incore detector system. A total of three core flux maps shall be taken with the movable incore detector system, one within each burnup window of BOL, MOL and EOL as defined in the Cycle 04 Nuclear Design Report. l Following completion of Cycle 04 operation, the licensee shall submit to the NRC a report showing compaL-ison of the fixed and movable incore detector flux map results (Fq, Fxy and FAh);

comparing Cycle 3 and Cycle 4 with the YAEC-1855P values.

If the Cycle 03 and Cycle 04 comparisons continue to demonstrate consistency with the results previously provided to the NRC for Cycle 01 and Cycle 02, then the NRC would no longer require l l

further confirmatory movable incore detector flux map data. j l

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REFERENCE:

1. North Atlantic Letter NYN-92162, dated November 25, 1992,

" License Amendment Request 92-14: Incore Detector System,"

T. C. Feigenbaum to USNRC.

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2. J. P. Gorski, "Seabrook Station Unit 1 Fixed Incore Detector System Analysis," YAEC-1855P, Yankee Atomic Electric Co.,  !

October 1992.  ;

3. North Atlantic Letter NYN-93098, dated July 2, 1993,

" Response to Request for Additional Information: License Amendment Request 92-14," T. C. Feigenbaum.

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ENCLOSURE 2 SYSTEMATIC ASSESSMENT OF LICENSEE PERFORMANCE Facility Name Seabrook Nuclear Power Station Summary of Review The SER involved a review of YAEC-1855P which was performed during July 1993 - October 1993 by the Reactor Systems Branch /DSSA/NRR. Based on its review, the staff concludes that the report is acceptable for referencing for use in Seabrook Station Unit 1.

NARRATIVE DISCUSSION OF LICENSEE PERFORMANCE - SAFETY ,

ASSESSMENT /OUALITY VERIFICATION The licensee addressed all aspects of the issues in their initial submittal in their response to request for additional information and in meetings with the staff. This achievement indicated good interdepartmental communications, a technically qualified staff,  ;

and responsiveness to NRC 1ssues.

AUTHOR: G. Schwenk DATE: 10/21/93 P

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