ML20247L293
| ML20247L293 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 03/27/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20247L266 | List: |
| References | |
| NUDOCS 8904050426 | |
| Download: ML20247L293 (2) | |
Text
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[ga arog '9 UNITED STATES
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E WASHINGTON, D. C. 20555
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMEtiDMENT NO. 34 TO FACILITY OPERATING LICENSE NO. DPR-80 AND AMEN 0 MENT N0. 33 10 FACILITY OPERATING LICENSE N0. DPR-82 PACIFIC GAS AND ELECTRIC COMPANY DIABLO CANYON NUCLEAR POWER PLANT, UNIT NOS. 1 AND,2 DOCKET N05. 50-275 AND 50-323
1.0 INTRODUCTION
By letter dated Ap(PG&E or the licensee) requested amendments to theril 18, 198 Electric Company Technical Specifications (TS) aprended to Facility Operating License Nos. DPR-80 and DPR-82 for the Dislo Canyon Nuclear Power Plant, (DCNPP) Unit Nos. I and 2, respectively. The proposed amendments would change the DCGDP Combined Technical Specifications by revising TS 2.2.1,
" Reactor Trip System Instrumentation Setpoints," Table 2.2-1, " Reactor Trip System Instrumentation Trip Setpoints," Items 13 and 14 to reduce the steam generator water level low and low-low setpoints from 15 to 7.2 percent of the narrow range span.
Also, the associated TS bases would be changed accordingly.
2.0 EVALUATION The NRC staff has evaluated the proposed changes and has concluded that they are acceptable. The staff's evaluation is given below.
The purpose of the change as stated by)PG&E is to decrease the number of unnecessary reactor trips caused by (1 ste m gener4 tor water level low-low and (2) steam generator water level ow coincident with steam /feedwater flow mismatch.
This will in turn reduce the number of challenges to the reactor protection systems and impose fewer thermal transients on the plants.
The primary change proposed to support the setpoint reduction involves the replacement of the existing Rarton 764 steam generator level transmitters with more accurate Rosemount 1154 transmitters. The actual reduction proposed would be from 15% to 7.2% of the narrow range span.
As part of the proposed change, PG&E provided WCAP-11784, " Calculation l
of Steam Generator Level Low and Low-Low Trip Setpoint With Use of a I
Rosemount 1154 Transmitter," dated March 1988. The non-proprietary version (WCAP-11785) was also provided. The staff also reviewed the 8904050426 690327 DR ADOCK 05000275 PDC
i i q PG&E design calculation sheets related to the accuracy of the new transmitters.
4 The methodology used to calculate the setpoints as described in WCAP-11784 is similar to the netho:fology previously approved by the staff for the V. C. Summer Plant (NUREG-0717 SSER #4 August 1982).
Based on similarity, the staff considers the setpoint methodology to be.
acceptable. This methodology is a statistical (square root of the sum of the squares) method.
The two largest contributors to the original 15% setpoint (reference PG&E letter to F. J. Miraglia (NRC) dated February 19,1981) involved post accident transmitter error and an additional margin of safety. The proposed Rosemount transmitters have been type-tested by IEEE Standards 323-1974, 323-1983 and 344-1975. This testing involved baseline accuracy-tests, radiation tests, functional tests,. LOCA/high energy line break tests, one year post accident simulation and a final functional test.
Accicent test levels were chosen to encompass the Diablo Canyon postulated accident environment. The tests show the proposed Rosemount j
transmitters to be more accurate than the original Barton equipment during the postulated accident environment.
Based on this, the staff does not require an additional margin for safety for this equipn'ent.
The additional margin had originally been required due to the inaccuracies of the Barton transmitter when operated at the lower end of its scale. Due to the accuracy demonstrated by testing, the staff finds 2
the removal of the edditional margin acceptable for these Rosemount transmitters.
Therevisedsetpointcalculation(usingWCAP-11784)showsthatthe improved accuracy of the Rosemount transmitters ccmbined with the improved setpoint calculation methodology as compared to the original 15 percent calculation allows the steam generator water level 1cw-low setpoint to be reduced to 7.2 percent of the narrow range instrument span. The staff finds both the above change and the corresponding allcwable value of 6.2 percent as shown on the proposed technical specification to be acceptable. The staff also finds the same change for the steam generator water level low with steam flow / feed flow mismatch reactor trip to be acceptable, for the same_ reasons.
In summary, the staff has reviewed the proposed revision of Technical Specification 2.2.1 and for the reasons given above, finds the changes described in the April 18, 1988 PG&E submittal to be acceptable.
3.0 ENVIRONMENTAL CONCLUSION Pursuant to 10 CFR 51.21, 51.32, and 51.35, an Environmental Assessment and Finding of No Significant impact has been prepared and published (54 FR 12032) in the Federal Register on March 23, 1989. Accordingly, based upon the environmental assessment, the Commission has determined that the issuance of the amendments will not have a significant effect on the quality of the human environment.
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