ML20033B312
| ML20033B312 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 11/05/1981 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20033B308 | List: |
| References | |
| NUDOCS 8112010218 | |
| Download: ML20033B312 (2) | |
Text
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SAFETY' EVALUATION ~BY THE'0FFICE OF' NUCLEAR' REACTOR' REGULATION SUPPORTING AMENDMENT NO.' 8 T0 ' LICENSE 'NO.~ 'DPR-22 NORTHERN STATES' POWER: COMPANY DOCKET N0. 50-263 MONTICELLO NUCLEAR GENERATING PLANT
'l.0 Introduction By letter dated June 4,1981 Northern States Power Company (the licensee)
' requested changes to the Technical Specifications (Appendix A) appended to Facility Operating License No. DPR-22 for the Monticello Nuclear
' Generating Plant. The requested changes reflect plant modifications being made as part of the Mark I Containment Long-Term Program.
2.0 Background Information Monticello currently has ten 18-inch Atwood and Morrill vacuum breakers on the end of the eight vent lines in the pressure suppression chamber (torus).
Six of these vent lines fiave one vacuum breaker and two of the vent lines have two vacuum breakers. As part of the Mark I Containment Long-Term Program, the licensee has reevaluated vacuum breaker sizing requirements.
The licensee determined that the limiting transient occurs with both drywell sprays initiated simultaneous'.y in a steam filled drywell (following onset of a LOCA). Northern States Power Company also determined that six vacuum breakers would keep the torus to drywell differential pressure we' 5elow the two p id design pressure.
Based on this finding, the licensee proposed changing the Technical Specifica-tions to require that eight vacuum breakers be operable under normal conditions in lieu of the current requirement of ten operable vacuum breakers.
3.0 Evaluation 1:
Torus - Drywell Vacuum Breakers The licensee has evaluated the following cases: (1) inadvertent spray operation; (2) drywell spray following onset of a LOCA; and (3) vessel reflood through the postulated break. The licensee determined that the limiting transient occurs for drywell spray following onset of a LOCA and that six vacuum breakers would keep torus-to-drywell differential pressure wen below the 2 psid design limit.
8112010218 811105 DR ADOCK 05000263 PDR
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2 We have performed indepbndent confirmatory calculations and agree with the licensee's conclusion that six vacuum breakers are sufficient to keep the torus to drywell differential pressure below the design value.
Based on this finding, we conclude it would be preferable for the licensee to mount only eight vacuum breakers on the vent lines in the
' torus instead of the ten vacuum breakers called for in the existing Technical Specifications.
Reducing the total number of vacuum breakers from ten to eight would also reduce the potential for drywell-torus bypass leakage.
Accordingly, we find the licensee's proposed Technical Specification changes acceptable.
4.0 Environmental Considerations We have determined that the amendment does not involve a change in effluent types or total amounts nor an increase in power level and will nct result in any significant environmental impact.
Having made this determination, we have further concluded that the amendment involves an action which is insignificant from the standpoint of environmental impact and pursuant to 10 CFR Section 51.5(d)(4) that an environmental impact statement or negative declaration and environmental impact appraisal need not be prepared in connection with the issuance of the amendment.
5.0 Conclusions 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 singificant decrease ~ in a safety margin, the amendment does not involve a significant hazards consideration, (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manr.,, and (3) such activities will be conducted in compliance with the Commission's regulations and the issuance of the amendment will not be inimical to the common defe.nse and security or to the health and safety of the public.
Dated:. November 5, 1981