ML19256E347
| ML19256E347 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 10/18/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19256E343 | List: |
| References | |
| NUDOCS 7911020208 | |
| Download: ML19256E347 (3) | |
Text
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uq'o, UNITED STATES NUCLEAR REGULATORY COMMISSION
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATInn SUPPORTING AMENDMENT NO. 29 TO FACILITY OPERATING LICENSE No. DPR-6 CONSUMERS POWER COMPANY BIG RDCK DOINT DOCKET NO. 50-155
1.0 INTRODUCTION
By letter dated September 7,1979, Consumers Power Company (the licensee)
(CPC) sutmitted an application for a license amendment to modify the Big Rock Point Technical Specifications to incorporate a procedure for reactor startup in the event neutron source strength is below that which provides the currently specified minimum count rate on out-of-core nuclear Instrumentation.
2.0 DISCUSSION The Big Rock Point Plant was shutdown in early February 1979 for maintenance and refueling. The shutdown was extended and startup is schedulad for October 1979.
The existing Technical Specification 7.3.2(d) reouires a count rate of "a minimum of three counts per second with a signal-to-noise ratio of 3 to 1."
Due to the length of this shutdown theantimony-beryllium startup sources have decayed (half life of these sources is 60 days) to the point that the licensee estimates that startup count rates may be as low as 2 counts per second during the October 1979 startup. The licensee also estimates that the signal-to-ncise ratio may also be less than 3 to 1.
In order to solve this problem CPC has proposed a revision to the Technical Specification to allow approach to criticality for reactor startup when the neutron source strength is insuf fici.t to produce the currently required count rate provided specifiec conditions are met.
The authorization would also be used for any subsequent startups as may be necessary until sufficient power operation has been accumulated to irradiate the antimony-beryllium sources sufficiently to produce the required count rate.
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. 3.0 EVALUATION This change would allow a critical approach with the reactor vessel head off to evaluate the out-of-vessel low-level detector response and control rod withdrawal sequence.
(A critical approach with the reactor vessel head off is part of the nomal startup). Temporary low-level detectors would be inserted in the core for this critical approach. These temporary detectors must meet the minimum 3 counts per second and the 3 to 1 signal-to-noise ratio. During thiscritical approach all seven out-of-core instruments (two startup range, two intermediate range and three power range monitors) will be inservice.
Count rate vs. control rod configura-tion and keff for both the temporary detectors and the startun range monitors will be recorded throughout the critical approach.
By the time the predicted.995 keff rod pattern is reached the out-of-core startup range monitors count rate and signal-to-noise ratio will be checked to be certain they meet the 3 cps and 3 to 1 signal-to-noise ratio.
The actual critical rod pattern will be compared with the predicted pattern.
A new.995 k pattern will be obtained if necessary and the count rate and signal-to-nob ratio for this new.995 keff pattern will be compared with the minimum 3 cps and 3 to 1 sigrial-to-noise ratio criteria.
Prior to the head-on critical approach tia tenporary detectors would be removed. Signal-to-noise ratio and gross count rate for the startup range monitor with all rods inserted are expected to be near but could possibly be less than the specified minimum values.
If startup range monitor count rate and signal-to-noise ratio do not meet the requirenents of Technical Specifications Section 7.3.2(d), the control rods will be withdrawn in a pattern identical to that for the head-off critical and startup range monitor 1/m plots as a function of keff will be compared to those generated with the startup range monitors for the head-off critical.
If, prior to or at the time of the estimated.995 keff control rod configuration established during the head-off critical approach is attained, a minimum signal-to-noise ratio of 3 to 1 and a gross count rate of greater than or equal to 3 cps are displayed by the startup range monitors, normal startun will continue. All rods will be returned to their fully inserted positions should these instrumentation requirements not be met by the time the head-off.9Pc kaf control rod configuration is attained.
The head-off.995 keff control rod pattern allows.5% marain prior to criticality.
It is also more than twice the maximum predicted notch worth in this part of the rod withdrawal sequence and.2% greater than the Technical Specification limit for notch worth.
Since the predicted notch worth near criticality i:. usually about.1%, the.995 keff p sition represents a rod pattern about 5 notches from criticality.
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. The compter code used for the.995 keff and critical predictions is GROK.
It has been used very successfully for the past 6 cycles. Startup test measurements for these cycles have all agreed with GROK predictions within.5% and many of the measurements have been within.1% of prediction.
Based on the above infonnation, we conclude that the use of temporary detectors to establish the control rod withdrawal sequence and to evaluate the out-of-vessel startup range monitors response for the upcoming operation is acceptable.
We also find that the comparison of the head-on 1/m plots as a function of keff with those obtained for the head off critical using the identical control rod withdrawal sequence is reasonable.
However, the GROK code is presently being reviewed by the NRC.
Since this review is not completed, we cannot approve this technical specification change on a permanent basis.
But, in light of the excellent agreement between GROK predictions and the actual measurements for tha last 6 cycles together with the comparison of the 1/m plots for the head-off and head-on critical approaches, we find this change acceptable for the October 1979 startup and Cycle 16 operation. We have revised the proposed technical specification to limit its applicability to Cycle 16 operation. We have informed CPC representatives of this revision and they find the revision to be accc; ta ble.
4.0 ENVIR0fNENTAL CONSIDERATION We have determined that the amendment does not authorize a change in effluent types or total amounts nor an increase in power level and will not result in any significant environmental impact. Having made this determination, we have further concluded that the amendment involves an action which is insignificagt from the standpoint of environmental impact and pursuant to 10 CFR f51.5(d)(4) that an envirormental impact statement or negative declaration and envirormental impact appraisal need not be prepared in connection with the issuance of this amendment.
5.0 CONCLUSION
S We have concluded, based on the considerations discussed above, that:
(1) because the amendment does not involve a significant increase in the probability or consequences of accidents previously considered and does not involve a sipificant decrease in a safety margin, the amendment does not involve a significant hazards concideratlon, (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (3) such activities will be conducted in compliance with the Commission's regulations and the issuance of this amendment will not be inimical to the comon defense and security or to the health and safety of the pu blic.
Date:
October 18, 1979 c]
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