ML19274D456
| ML19274D456 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 01/12/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19274D454 | List: |
| References | |
| NUDOCS 7902010193 | |
| Download: ML19274D456 (2) | |
Text
.
p n*Ecm UNITED STATES
/
NUCLEAR REGULATORY COMMISSION yg g
4r
{,,W j j WASHINGTON, o. C. 20555 e
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 58 TO PROVISIONAL OPERATING LICENSE NO. DPR-21 NORTHEAST NUCLEAR ENERGY COMPANY MILLSTONE NUCLEAR POWER STATION, UNIT 1 DOCKET NO. 50-245 Introduction In a letter dated March 15, 1978, the Northeast Nuclear Energy Company (the licensee) proposed a change to the Technical Specifications for the Millstone Nuclear Power Station Unit No.1.
This change would revise the setpoint for the suppression chamber to reactor building vacuum breakers from 0.5 psid to a range of 0.4 to 0.5 psid.
This change was requested to permit greater flexibility in the vacuum breaker valve maintenance and adjus".1ent procedures.
Discussion and Evaluation The suppression chamber to reactor building vacuum breaker system has been designed to limit the external differential pressure acting on the containment structure in the event of a negative pressure transient in either the drywell or suppression chamber. This vacuum breaker system consists of redundant lines, each containing a check valve in series with a nomally-closed, air-operated butterfly valve. The containment pressure response and vacuum breaker sizing analysis has been based on the assump-tion that the vacuum breaker valves would begin to open at an external pressure differential of 0.5 psid. The check valve is adjusted to open when a force equivalent to an external pressure differential of 0.5 psid acts on the valve disc, while the butterfly valve receives a differential pressure signal to open.
These valves which serve as containment isolation barriers to limit tha release of fission products from the contakment atmosphere for all other transient events are normally closed. To provide added assurance that the valves are closed and the containment isolated except when valve opening is necessary to protect the structural integrity of the containment, a lower hound on the vacuum breaker setpoint is ee,tablished to reduce the probability of inadvertent or spurious opening of these valves. The licensee has proposed a lower bound on the vacuum breaker setpoint of 0.4 psid. We find based on the licensee's operating experience that this value provides sufficient margin to preclude ina/ 1rtent operation of the vacuum breakers during normal barometric chan
, or pressure fluctuations.
7902010l93
. The revised setpoint will not change the technical specification design basis for the vacuu.J breaker performance, nor will it potentially jeopardize the containment integrity. Should an accident occur while the vacuum breaker valves are open, the increased pressure inside containment will causa such valves to close imediately so that the proposed amendment will not affect the release of radioactivity. On this basis, we find the proposed setpoint change to be acceptable.
Environmental Consideration We have detemined that 1,the amendment db 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 detemination, we have further concluded that the amendment ir/.tives an action which is insignificant from the standpoint of environmental impact and, pursuant to 10 CFR 251.5(d)(4), that an environmental impact state-ment or negative declaration and environmental impact appraisal need r.ot be prepared in connection with the issuance of this amendment.
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 haiards car, sideration, (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 common defense '
and security or to the health and safety of th public.
Date: January 12, 1979
.5