ML19345D223
| ML19345D223 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 11/21/1980 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19345D217 | List: |
| References | |
| NUDOCS 8012120272 | |
| Download: ML19345D223 (3) | |
Text
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 30 TO FACILITY OPERATING LICENSE NO. DPR-54 SACRAMENTO MUNICIPAL UTILITY DISTRICT RANCHO SECO NUCLEAR GENERATING STATION DOCXET N0. 50-312 Introduction By letter dated August 11, 1980, Sacramento Municipal Utility District (the licensee) requested an amendment to the Rancho Seco Technical Specifications (TSs) appended to Facility Operating License No. DPR-54 The proposed amend-ment would change the " flux-to-flow" ratio from the present value of 1.05 to a new value of 1.08.
Discussion The requested change in TSs will prevent inadvertent challenges to the Reactor Protection System resulting from Reactor Coolant System (RCS) flow oscillations.
Flow oscillation indication in the RCS is attributed to the recent adjustment of flow " snubbers" installed in the flow instrumentation sense lines.
In the Rancho Seco loss of flow transient analysis, the licensee assumed that the delay to the flow signal, due to the presence of the snubbers in the instrument lines is 1.0 second. Because of a reduction in reactor coolant flow resulting from the installation of 52 Burnable Poison Rod Assemblies (BPRAs) into the core during the Cycle 4 reload, and in anticipation of potentially exceeding the 1.0 second delay limit during the startup test for Cycle 4, the licensee decreased the damping effect of the snubbers so that the delay time would be decreased and, therefore, meet the analysis assumption.
l During the reactor startup test program, the delay time was measured to be about 0.70 second (Ref.1). liowever, the effect of decreasing the damping of the flow snubbers was to render the flow transmitters more sensitive to rapid flow changes.
The increased flow measuring sensitivity, coupled with the existing flux-to-flow trip setpoint of 1.05, was found to cause spurious reactor trips if the reactor l
power was raised above 96% while at full flow. The licensee chose to operate at no higher than 96% power until the situation is modified.
To modify this situation, the licensee is requesting a TS change of the flux-to-flow trip set-point to the higher value of 1.08.
Evaluation For this evaluation, the following RCS flow rates are germane and are listed for clari ty:
GPM
% Design Design 369,600 100 TSs 387,600 104.9 Measured 404,820 109.5 80121204 M
. Previous analysis utilizing the existing flux-to-flow setpoint of 1.05 and the design flow rate of 369,600 gpm indicated a minimtsr Departure from Nucleate Boiling Ratio (DNBR) margin of approximately 10.5%. Justification for increasing the flux-to-flow setpoint from 1.05 to 1.08 is based upon the licensee taking ci
. for the additional flow allowed by the TSs. Utilizing a flow rate of 387,600 gpm and a flux-to-flow setpoint of 1.08, the licensee analyzed the effects of the change in the flux-to-flow setpoint on transients that involve a flux-flow mismatch. Results of the analysis indicate that a minimum DNBR margin in excess of 10% remains throughout the transients. This DNBR margin is acceptable.
Uncertainty of the measured RCS flow rate is indicated to be +2.5% by the licensee (Ref. 2). With a +2.5% uncertainty in the currently measured four pump full flow rate of 404,E20 gpm, the minimum required TS flow rate of 387,600 is not violated. The licensee assures and we agree that the minimum TS flow rate is always achieved by using the measured flow of 404,820 gpm as the 100% flow figure rather than using the TS figure of 387,600 gpm. Utilizing this methodology, subsequent reduction in flow throughout plant lif7 would necessitate a corresponding identical reduction in reactor power (i.e., if the flow instrumentation indicated 387,600 gpm, the actual flow could be 2.5% less, but the indicated flow for the flux-to-flow trip would be 95.7% which would result in a reduction in the maximum allowable power level to 95.7 x 1.08 =
103.4% (Ref. 2)).
An additional protective feature at Rancho Seco is the 105.5% overpower trip, which will remain unchanged. Should the reactor be operating at full power and at full flow rate, and a malfunction cause a power rise, the overpower reactor trip will scram the reactor before the flux-to-flow setpoint of 1.08 is reached.
Based on the above, it is deemed that the requested change to the TSs does not compromise any safety requirements, and we therefore find it acceptable.
Environmental Consideration f
We have detemined 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 t.
< detemination, we have further concluded that the amendment involves an action which is insignificant from the standpoint of environmental impact and, pursuant to 10 CFR 551.5(d)(4), that an environmental impact statement, or negative declaration and environ-mental impact appraisal need not be prepared in connection with the issuance of this amendment.
l
Conclusion 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 significant decrease in a safety margin, the amendment does not involve a significant ha:ards consideration (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 coeren defense and security or to the health and safety of the public.
Dated: November 21, 1980 References 1.
Letter, R. J. Rodriguez (SMUD) to Director, I&E (NRC), dated July 7,1980.
2.
Letter, J. J. Mattimoe (SMJD) to R. W. Reid (NRC), dated November 10, 1980.
.