ML20006C054
| ML20006C054 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 01/26/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20006C052 | List: |
| References | |
| NUDOCS 9002060245 | |
| Download: ML20006C054 (3) | |
Text
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~ NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20566 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO.118 TO FACILITY OPERATING LICENSE NO. DPR-28 i
VERMONT YANKEE NUCLEAR POWER CORPORATION VERMONT YANKEE NUCLEAR POWER STATION l
DOCKET NO. 50-271 l
1.0' INTRODUCTION By letter dated November 9, 1989, the Vermont Yankee Nuclear Power Corporation (the licensee) requested an amendment to Facility Operating License No. DPR-28 for the Vermont Yankee Nuclear Power Station. The proposed amendment would extend the out-of-service time for the Uninterruptible Power Supply (UPS) from 7 to 30 days in the Limiting Conditions for Operation (LCO) in Technical i
Specification (TS)3.5.A.4 I
2.0 BACKGROUND
The proposed change extends the present LC0 for an inoperable UPS from 7 days to 30 days until-the forthcoming refueling outage (Fall,1990). Those low pressure coolant injection (LPCI) valves which are normally powered by the.UPS would be connected to an alternete power supply from the onsite 480-Vac-L
. emergency power distribution system whenever either UPS-1A or -18 is inoperable.
The licensee committed in their November 9, 1989 letter to replace the:
-j l-existing UPS System prior to startup-from the 1990 refueling outage. These TS will'be reviewed, at that time, for suitability with the-new.UPS System.- On November.5, 1989, UPS-1A was declared inoperable, the licensee found that i
p obtainino parts and making-necessary repairs during the required 7-day LCO i
l became increasingly difficult over time, as Class 1E equipment has-generally
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E become more difficult to procure. Therefore, on November 9, 1989, the NRC L
granted a Temporary Waiver of Compliance from TS section 3.5.A.4 in response to the licensee's November 9, 1989 letter. This allowed that the subject LCO be extended from 7 days to 30 days. The waiver expired on December 11, 1989, i
L Although an effort to restore the UPS was successful and the waiver was not L
needed, the licensee determined that the subject TS relief may still be L
advisable until a new UPS system is installed.
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3.0 EVALUATION j
l The UPS'is the normal power supply used to provide 480-Vac Class IE power to
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l LPCI valves.
It is used to reposition certain LPCI valves during the initiation of a LOCA. An alternate power supply from the onsite emergency power distribution system is also available when a UPS is found to be inoperable.
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-The UPS system was'added when the loop selection logic, which required a swing-bus and a. bus ~ transfer scheme, was removed at VY in 1976. Since the swing bus-transfer scheme was susceptible to a single failure which could prevent the-swing bus from seeking its alternate AC power, a total loss of LPCI function could occur. Thus, the UPS design was incorporated to provide independent power sources to the LPCI valves assigned to each split-bus to enhance the reliability of the LPCI system.
Upon an ESF actuation, both UPSs automatically isolate from the emergency buses-(8 & 9), but continue to supply power to the LPCI valves (MCC 89A & 898) from the UPS, completely independent of the onsite power distribution system.
Thus, it eliminates any single failure vulnerability resulting from the onsite emergency power source failures (AC & DC).
The licensee's November 9, 1989 request identified the worst case accident scenario during the extended LCO period with an inoperable UPS as follows:
1)
Loss of all offsite power 2) a double-ended recirculation discharge break in one loop (LOCA) 3)
a single failure of emergency diesel generator (EDG) which supplies power to the LPCI valves and pumps in the other unbroken) loop Under this scenario, the licensee finds that both LPCI loops and one core spray pump would not be available, thus leaving only one core spray pump to perform ECCS functions.
The licensee stated that the above scenario (i.e., single failure associated with EDG) is a very low probability event since the EDG buses can be powered from offsite AC power sources as well as from the nearby Vernon Hydro Station.
The staff has reviewed the onsite power distribution system with respect to the worst case accident scenario postulated by the licensee. We concur with the licensee that the LPCI valves assigned to the inoperable UPS could be connected to the already existing alternate onsite 480-Vac power distribution system by closing a maintenance tie when-the UPS is lost. The LPCI valves are also capable of being powered from either onsite EDGs or offsite power through the startup transformers..In addition, we find that the above LPCI valves can also be fed from the Vernon Hydro Station. For a loss of either normal power
_(offsite) or onsite EDG, the licensee demonstrated that the power transfer to the hydro station can be done manually in a matter of seconds from the control room and this switching operation is covered by the current plant procedures and operator training. The licensee also stated that the hydro station has been energized continuously, thus there is no need to startup any equipment and it has shown excellent reliability with a history of only two unplanned outages-(total of less than 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />) since 1965.
In addition, the licensee committed, as shown in the amended TS 3.5.A.4, that a 7-day out-of-service interval would not be exceeded unless the maintenance tie is available, the emergency diesel generators are operable and the 4160 volt tie line from Vernon Hydro is available.
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-4.0 DISCUSSION OF STATE'0F VERMONT'S COMMENTS
- By letter dated December 1,1989 the State of Vermont submitted coments on this proposed TS change request. The State was concerned about a potential reduction in the margin of safety by extending the outage time in the LCO from 7 to 30-days.
In Section 3.0 of this Safety Evaluation, we stated that the 7-day LCO would not be exceeded unless emergency power is available from both the Vernon Hydro and both diesel generators and the maintenance tie is available.
Therefore, operation, when permitted under the 30-day LCO, would present-the identical margin of safety as in the 7-day LCO.
The State' also expressed concern about the reliability of the Vernon Hydro Station and the ability of the plant operators to perform any needed power transfers from Vernon to the VY emergency busses. These concerns are also addressed in Section 3.0 of this Safety Evaluation.
5.0 ENVIRONMENTAL CONSIDERATION
This amendment involves a change in a requirement with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The staff has determined that the amendment involves no significant increase in the 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 Comission has previously published a proposed finding that the amendment involves no significant hazards consideration and while there was public comment on our finding, the comments did not result in.a~ change to our finding. Accordingly, this amendment meets the eligibility criteria for categoricalexclusionsetforthin10CFR51.22(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 this amendment.
6.0 CONCLUSION
' Based on our evaluation of the above worst case accident scenario and the licensee's comitments,-it is our judgement that a loss of all offsite power including the Vernon Hydro Station, a LOCA concurrent with an additional single failure which leaves one core spray to perform ECCS functions are a very unlikely coincidence of events during the extended 30-day LCO period with an inoperable UPS. Therefore, we conclude that this relief from the required 7-day requirements of the present TS until the next refueling outage is acceptable.
In addition, TS 3.5.A.4 would not permit a greater than 7-day out-of-service interval unless the maintenance tie, emerger.cy diesels and Vernon Hydro is an operable delayed access power source.
The staff 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 manner, and (2) such activities will be conducted in compliance with the Comission's regulations, and (3) the issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
P. Kang Dated: January 26, 1990
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