ML20210U503
| ML20210U503 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 08/13/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20210U499 | List: |
| References | |
| NUDOCS 9908200146 | |
| Download: ML20210U503 (3) | |
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4 UNITED STATER NUCLEAR REGULATOR'r COMMISSION 5
e WASHINGTON. D.C. 20555-0001 4.....,/
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.173TO FACILITY OPERATING LICENSE NO. DPR-28 VERMONT YANKEE NUCLEAR POWER CORPORATION VERMONT YANKEE NUCLEAR POWER STATION DOCKET NO. 50-271
1.0 INTRODUCTION
By letter dated June 24,1999, the Vermont Yankee Nuclear Power Corporation (the licensee) submitted a request to amend the Vermont Yankee Nuclear Power Station (VY) Technical Specifications (TSs). The proposed amendment clarifies the basis for the reactor protection system bypass of the turbine stop valve (TSV) closure and turbine control valve (TCV) fast closure scram signals at low power. The amendment clarifies that the analytical basis for this bypass corresponds to a fraction of reactor rated thermal power (RTP) and not other measures of power, for instance, turbine power.
2.0 EVALUATION A reactor scram is initiated at the start of TSV closure and TCV fast closure in anticipation of the reactor pressure and power transients that could result from the valves' closure when operating at power. For these events the reactor scram provides protection of the fuel and (in combination with the safety and relief valves) pressure vessel.
At low-power levels the pressure rise associated with the TSV and TCV closure events is not as rapid or as large as at higher power levels. The TCV fast closure or TSV closure scrams are unnecessary at low-power levels because the margins to fuel thermal limits and reactor coolant pressure boundary limits are large at low-power levels. Therefore, these scrams are automatically bypassed at low-power. The licensee stated that this automatic bypass is a design basis assumption in the transient analyses for VY. The diverse high neutron flux or high vessel pressure scrams are adequate to terminate the transients at low-power levels. The scram bypass power level is currently limited by the transient analysis to operation at or below 32.2 percent RTP. This is the reactor power level at which sufficient fuel thermal margin is available to allow bypass of the TSV and TCV based trips, and place reliance on the neutron flux or high pressure scrams to terminate over-pressure events.
The licensee stated that the TCV fast closure and TSV closure scram bypass are controlled by four pressure switches which sense turbine first-stage pressure. These switches have a setpoint, which is slightly lower than the analytical limit, that automatically removes the scram bypass when the turbine first stage pressure exceeds a preset value corresponding to 30 percent of reactor RTP. The lower operationallimit provides additional conservatism by maintaining the TSP and TCV trips functional to a lower power than required by the analysis.
9908200146 990813 PDR ADOCK 05000271 1
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- The licensee stated that a non-conservative first-stage pressure setpoint had been established at another facility because personnel responsible for defining the instrument setpoint were incorrectly led to believe that the basis for the setpoint was 30 percent of rated turbine power l
instead of 30 percent of rated RTP. To avoid confusion and the potential for erroneous I
setpoints with consequent non-conservative operation concerning this scram bypass signal, the licensee proposed the following changes to the TSs.
The licensee proposed changing TS 2.1, Limiting Safety System Setting, paragraphs E and F to indicate that the TSV scram and TCV fast closure scram are applicable "when operating at greater than 30 percent of rated thermal power".
The licensee also proposed changing Table 3.1.1, Reactor Protection System (Scram)
Instrument Requirements, Note 10 to read " Turbine stop valve closure and turbine control valve fast closure scram signals may be bypassed at s 30% of reactor Rated Thermal Power."
Previously this note stated that the scrams could be bypassed "when the first stage turbine pressure is less than 30% of normal (220 psia)."
The proposed amendment also changes the Bases sections of these TSs to reflect these clarifications.
l The staff finds the proposed changes to be acceptable since they will clarify that the subject scrams can be bypassed at less than 30 percent of reactor rated thermal power consistent with the design basis assumptions for VY and will prevent confusion with other measures of power, for instance, turbine power. The staff has no objection to the proposed Bases changes associated with this amendment request.
3.0 STATE CONSULTATION
i in accordance with the Commission's regulations, the Vermont State official was notified of the proposed issuance of the amendment. The State official had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The NRC staff has determined that the amendment involves no significant increase in 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 cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendment involves no significant hazards
- consideration, and there has been no public comment on such finding (64 FR 38038 ).
- 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 be prepared in connection with the issuance of the amendment.
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5.0 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 the proposed manr.er, (2) such activities will be conducted in compliance with the =
Commission's regulations, 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.
Principal Contributor: R. Crotea'u Date:
August 13, 1999 l
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