ML20076A678
| ML20076A678 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 06/26/1991 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20076A676 | List: |
| References | |
| NUDOCS 9107080195 | |
| Download: ML20076A678 (2) | |
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NUCLEAR REGULATORY COMMISSION WASHINGTON, D C. 205b5
%..., *,g SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 63 TO FACILITY OPERATING LICENSE NO. DPR-80 AND AMENDMENT NO.
62 TO FACILITY OPERATING LICENSE NO. DPR-82 PACIFIC GAS AND ELECTRIC COMPANY DIABLO CANYON NUCLEAR POWER PLANT, UNIT NOS.1 AND 2 DOCKET NOS. 50-275 AND 50-323 1.0 INTRODUCTIO By letter de.ted October le, 1990, Pacific Gas and Electric Company proposed a change to the Technical Specifications (TS) for the Diablo Canyon Power Plant (DCPF) Units 1 and 2.
The change to TS 3/4.2.4, " Quadrant Power Tilt Ratio" would perinit the determination of the Quadrant Power Tilt Ratio (QFTR) by either a full incore flux map or by symetric flux thimble measurement in the event that a single power range channel becomes inoperable above 75 percent of Rated Thermal Power (RTP). The existing DCPP TS permits only the use of four pairs of symetric core thimbles in this situation. The proposed change would avoid reduction in plant load and subsequent adjustment of Nuclear Instrumenta-tion System protection bistables in the event that one or more symetric flux thimbles is unavailable for flux mapping.
2.0 EVALUA110N The excore detectors are the sensors for the Nuclear Instrumentation System (NIS). At greater than 50 percent RTP, the NIS continuously monitors the QPTR.
It is important that changes do not go undetected and invalidate the radial power distribution assumed in the accident analyses. Excore detector inoper-ability is not a routine occurrence except for surveillance.
Inoperability has occurred due to events such as the failure of electronic components.
The Moveable Incore Detector System, or Flux Mapping System, is used to measure the actual core power distribution. A full core map and a symetric thinble map are two of the flux mapping methods referred to in the DCPP TS and plant procedures. The full incore map provides the most accurate representction of power distribution and is used for the monthly hot channel factor surveillance.
By TS 3.3.3.2, at least 75 percent of the 58 neutron detector thimbles aith a minimum of two detector thimbles per quadrant are required for a full core map.
In a symetric thimble map, eight of the core's fuel assemblies are monitored.
This type of map is used to verify that the actual radial power distribution is consistent with the NIS-measured QPTR when one power range channel is inoperable above 75 percent RTP.
All eight symmetric thimbles must be operable for the performance of a symmetric thimble map.
There is both industry and DCPP history of inoperable neutron detector thimbles for various reasons, if one of the eight symetric thimbles wers inoperable 9107000195 910626 PDR ADOCK 05000275 P
2 and a power range channel were also inoperable, plant output would have to be reduced to 75 percent RTP. This would not be necessary if a full incore flux map were permitted in this situation.
The proposed change has previously been approved at other facilities and is also consistent with the Draft Revision 5 of the Westinghouse Standard Technical Specifications.
The proposed change to permit QPTR determination by a full incore flux map as well as by symetric thimble measurement is warranted beca'Jse the full incore map is the most accurate method of determining core power distribution. Based on the above considerations, the Technical Specifi-cation change as proposed is acceptable, i
4.0 STATE CONSULTATION
In accordance with the Commission's regulations, the California State official.
was notified of the proposed issuance of the amendments. The State official had no coments.
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5.0 ENVIRONMENTAL CONSIDERATION
The amendments change a requirement with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and change a surveillance requirement. The NRC staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cvmulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public coment on such finding. Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(t ) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
6.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that:
(1) there '.s reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendnent will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
M. Chatterton Date: June 26,1991
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