ML20206J933

Safety Evaluation Supporting Amend 52 to License DPR-34

ML20206J933
Person / Time
Site:	Fort Saint Vrain
Issue date:	04/06/1987
From:	NRC
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Shared Package
ML20206J752	List: ML20206J748 ML20206J841 ML20206J933
References
TAC-55294, NUDOCS 8704160214
Download: ML20206J933 (3)

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/$ Ag UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 E j

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 52 TO FACILITY OPERATING LICENSE NO. DPR-34 PUBLIC SERVICE COMPANY OF COLORADO FORT ST. VRAIN NUCLEAR GENERATING STATION DOCKET NO. 50-267

1.0 INTRODUCTION AND BACKGROUND

By letter dated May 10, 1984 (P-84137), Pyblic Service Company of Colorado (PSC) requested the Circulator Speed-High Steam trip setting listed in Table 4.4-3 of the Fort St. Vrain Technical Specifications be changed. PSC stated that the proposed increase in trip setting would increase circulator availability while still providing for initiation of the necessary protective actions prior i to the maximum credible overspeed condition or the blade shedding 4 safety limit. This new setting would avoid unnecessary actuations of the circulator protective circuitry due to normal system transients - '

at or near 100% power operation. The proposed increase in maximum trip setting, from 11,000 rpm (115% of rated) to 11,700 rpm (123% of rated), would still provide the automatic protective actions

• conservatively prior to the credible overspeed condition (135%) as ,

1 designed. Due to the almost instantaneous overspeed reaction under

, postulated control or piping failures, the proposed increase would-be -

insignificant from a system sensing and time response standpoint.

- Additional information was provided in a letter dated December 27, 1984(P-84537).

2.0 EVALUATION 2.1 Materials Considerations It does not appear that the overspeed setpoint is, in any way, a materials engineering consideration because a change in the setpoint would not change the overspeed actually experienced by the turbine.

Therefore, from the materials aspect, such a setpoint change is of no consequence. It should be noted that the calculated blade shedding speed is 273% of design and the proposed setpoint increase is from B704160214 870406 -

{DR ADOCK 05000267 PDR

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115% to 123% of rated speed. Generally, a plant trip imposes themal stress upon materials and is, therefore undesirable, and, in l

the case of the subject turbine setpoint, unnecessary. The basis is that the higher setpoint will not increase the probability of an accident, but will decrease the number of plant trips. The staff therefore concludes that the higher setpoint would not involve a significant increase in the probability or consequences of an accident previously evaluated, nor create the possibility of a new or different kind of accident, nor involve a significant reduction in any margin of safety. Additionally, a r' eduction in trips would probably be beneficial to the materials involved.

2.2 Instrumentation Consideration '

The current setpoint for the trip of the helium circulator on steam -

turbine drive is 11,000 rpm. This provides protection to assure that the circulator does not exceed the design speed limit of 13,000 rpm.

For steam line ruptures downstream of the circulator steam turbine, the maximum speed is 13,264 rpm with.no centrol action or overspeed trip. Therefore, this event does not establish a limit for an acceptable high speed setpoint.

With the presently assumed overspeed trip value, the maximum transient ovespeed for a loss of restraining torque event (blade shedding) is 13,050 rpm. Reanalysis with an assumed overspeed trip value of 11,500 rpm results in a maximum transient overspeed of 13,267 rpm. Based on these ,

i analyses, it is extrapolated that an assumed overspeed trip at .

11,700 rpm would result in a maximum transient overspeed of 13,370 rpm or less.

Therefore, based on this analysis, the staff concludes that an assumed 4 overspeed trip value of 11,700 rpm provides an acceptable basis for .

I determining the trip setpoint for this protection function. With .

the allowance for instrument uncertainty the overspeed trip setpoint will be 11,495 rpm.

O 2.3 Systems Consideration The circulator trip overspeed function is primarily provided to protect the individual circulators from damage due to an overspeed transient. However, even the loss of an individual circulator is not critical, since only one of four circulators is needed for safe shutdown. Hence, this change to an equipment protective function has very little consequence for overall plant safety, and is, therefore, acceptable.

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3.0 ENVIRONMENTAL CONSIDERATION

The amendment involves a change in the installation or use of a ,

facility component located within the restricted area. The staff.has determined that the amendment involves no significant increase in the '

amounts, and no significant change in the types, of any effluents L

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l 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 this amendment involves no significant hazards consideration and there has been no public comment on such finding. Accordingly, this amendment meets the eli for categorical exclusion set forth in 10 9). CFR $51.22(c)(gibili Pursuant to 10 CFR 551.22(b), no Environmental Impact Statement or Environmental Assessment need be prepared in connection with the issuance of this amendment.

4.0 CONCLUSION

We have 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 manner, and (2)'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 the public. ,

Dated: April 6, 1987 Principal Contributor: K. Heitner, DPWRL-B t

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