ML20059B041
| ML20059B041 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 12/22/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20059B031 | List: |
| References | |
| NUDOCS 9401030263 | |
| Download: ML20059B041 (4) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO, 27 TO FACILITY OPERATING LICENSE NO. NPF-86 NORTH ATLANTIC ENERGY SERVICE CORPORATION SEABROOK STATION. UNIT NO. 1 DOCKET NO. 50-443
1.0 INTRODUCTION
By application dated November 25,1992 (Ref.1), as supplemented by letters of July 2, 1993, and November 24, 1993, North Atlantic Energy Service Corporation (North Atlantic /the licensee) proposed an amendment to the Appendix A Technical Specifications (TS) for the Seabrook Station, Unit 1 (Seabrook).
The proposed amendment would revise the TS with regard to requirements for use of the movable incore detectors to perform certain core measurements.
The proposed changes would allow the use of either the fixed incore detector system or the movable incore detector system to perform TS surveillances.
Specifically, the amendment modifies TS Sections 3.1.3, 4.2.2, 4.2.3, 4.2.4, and 3.3.3.
2.0 BACKGROUND
Seabrook contains two complete and independent incore detector systems. The first is a movable incore detector system, which uses movable fission chambers 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 platinum incore detector (fixed incore detector system) 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 factors which are used to establish limits using a method similar to the one used with the movable incore detector system. A detailed description of the fixed incore I
detector system is given in Section 2.0 of YAEC-1855P (Ref. 2).
1 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 System and to define the uncertainty for these i
power distribution measurements.
It is North Atlantic's intention to use.the fixed incore detector system as the primary power distribution measurement system with the movable incore detector system serving as a backup.
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3.0 EVALUATION The previously approved CASM0-3/ SIMULATE-3 code package is used as the i
analytical method for the prediction of neutron detector 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 detectors is a function of both the j
in:ident gamma and neutron flux. The gamma portion of the detector signal is i
dr.termined 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 4
operational data and public domain studies and was not the subject of a j
rigorous testing program.
The methods and calculations described in YAEC-1855P were applied to more than 20 power distribution measuremer.ts taken during Cycle 1 and 2 operation at Seabrook. 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 specific to the analytical physics methods, CASM0-3/ SIMULATE-3, used at '
Yankee,'the incore data processing code, FINC, and the platinum fixed incore detectors currently in use at Seabrook.
1 Based on the staff's review of YAEC-1855P, the staff finds the methods employed 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.
f The staff finds that the changes are based on applicable regulatory guidance in Standard Review Plan 5.2.2 (Revision 2), are reasonably conservative, and i
are acceptable.
However, for the following reasons, the NRC staff finds that both systems should be used until additional benchmark data can be obtained:
1.
First, there is a burnup dependence in the fixed / movable inferred measured Fxy and Fq. North Atlantic provided information (Ref. 3) to respond to this concern that shows that the difference most likely is due to the inherent differences in the reactor physics methods used to predict the power distribution. While this may be true, it is important that the ratic be monitored in future cycles to ensure that the two methods do not continue to diverge which would indicate a problem with one of the systems.
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2.
The fraction of the total signal which is due to neutrons is approximate,-is not a well know number, and it 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.
Third, there is little experience in the United States with a fixed platinum detector system.
Seabrook is the first plant to be approved to use this system for TS surveillance, and Seabrook is the first i
Westinghouse plant to employ a fixed incore detector system to determine core peaking factors.
The staff discussed these concerns with North Atlantic.
In response, North Atlantic has committed (Ref. 4) to the following actions:
1.
For the remainder of the current Cycle 3 operation, North Atlantic sill acquire at least one additional core flux map with the movable incore detector system within the burnup window of end-of-life (E0L) as defined in the Cycle 3 Nuclear Design Report. Eleven Cycle 3 core flux maps have been taken to date with the movable incore detector system.
2.
During Cycle 4 operation, North Atlantic will acquire additional core flux map data from the movable incore detector system. At least three core flux maps will be taken with the movable incore detector system, one within each burnup window of beginning-of-life (BOL), middle-of-life (MOL) and E0L as defined in the Cycle 4 Nuclear Design Report.
3.
Following completion of Cycle 4 operation, North Atlantic will submit to i
the NRC a report showing comparison of the fixed and movable incore detector flux map results (Fq, Fxy and FAh) comparing Cycle 3 and Cycle 4 with tne (AEC-1855P values.
If the Cycle 3 and Cycle 4 comparisons continue to demonstrate consistency with the results previously provided to the NRC for Cycle 1 and Cycle 2, then the NRC will no longer require i
further confirmatory movable incore detector flux map data.
4.0 STATE CONSULTATION
In accordance with the Commission's regulations, the New Hampshire and Massachusetts State officials were notified of the proposed issuance of the amendment. The State officials had no comments.
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5.0-ENVIRONMENTAL CONSIDERATION 1
The amendment changes requirements with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR t
Part 20 and changes surveillance requirements. The NRC staff has determined that the amendment involves no significant increase in the amounts, and no i
significant change in the types of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendment involves no significant hazards l
consideration, and there has been no public comment on such finding i
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l (58 FR 7002). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need i
be prepared in connection with the issuance of the amendment.
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6.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in tne proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, i
and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
7.0 REFERENCES
1.
North Atlantic Letter NYN-92162, dated November 25, 1992, " License Amendment Request 92-14:
Incore Detector System," T. C. Feigenbaum to USNRC.
2.
J. P. Gorski, "Seabrook Station Unit 1 Fixed Incore Datector System Analysis,".YAEC-1855P, Yankee Atomic Electric Co., October 1992.
I 3.
North Atlantic Letter NYN-93098, dated July 2,1993, "Rasponse to Request for Additional Information: License Amendeant Request 92-14,"
T. C. Feigenbaum to USNRC.
4.
North Atlantic letter NYN-93161, dated Nuvember 24, 1993. " Response to 1
Request [for] Additional Information: License Amendment Request 92-14 i
(TAC No. M85020)," T. C. Feigenbaum to USNRC.
Principal Contributors:
E. Kendrick G. Schwenk Date: December 22, 1993 1
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