ML20128A159
| ML20128A159 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 11/20/1992 |
| From: | Buckley B Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20128A165 | List: |
| References | |
| NUDOCS 9212030221 | |
| Download: ML20128A159 (5) | |
Text
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7590-01 UNITED STATES NUCLEAR REGULATORY COMMISSION VIRGINTA ELECTRIC AND POWER COMPANY DOCKET NO. 50-339 ENVIRONMENTAL ASSESSMENT AND FINDING OF NO SIGNIFICANT IMPACT The U.S. Nuclear Regulatory Connission is considering issuance of an exemption from the requirements of 10 CFR 50.49 to Virginia Electric and Power Company (the licensee), for the North Anna Power Station, Unit No. 2 (NA-2)
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located in Louisa County, Virginia.
ENVIRONMENTAL ASSESSMENT Identification of Procosed Aq11gn:
The proposed exemption would allow temporary relief from the requirements of 10 CFR 50.49, Environmental Qualification of Electric Equipment Important to Safety for Nuclear Power Plants. The temporary relief would be for the environmental qualification of the NA-2 control room chillers for the work activities associated with the Phase 1, Stage 1 Service Water Restoration Prcject (SWRP).
The Phase 1, Stage 1 will be performed concurrently with the NA-1 Steam Generator Replacement Program (SGRP). This exemption would permit temporary cooling of the NA-1 control room chillers from the common bearir.g cooling water system to provide normal control room temperatures and provide a reliable backup cooling systeu to the NA-2 air conditioning design basis. The period for the NA-1 chillers to be operating on bearing cooling water is projected to be between 90 and 120 days.
NA-162 each have three ccatrol room air conditioner chillers located in a missile protected rocm of the service building off the respective unit's turbine building basement.
Ventilation of each unit's chiller room is taken 9212030221 921120 PDR ADOCK 05000339 P
pon
l 1 fron and exhausted to the respective unit's turbine building basement. Hence, the chillers for each unit are located in the same environmental zone which is also common to the unit's turbine build %g basement. Therefore, as the result of an environmental qualification evaluation of the control room air conditioning systems, a station standing order was issued to require at least one of the opposite uait's chillers to remain oparable while in a shutdown condition.
Specifically, the station standing order requires that at least one control roo'n chiller on the unit in Mode 5 or 6 be maintained operable while the other unit is in Mode 4 or above. This measure assures that the air conditioning system serving the control room and emergency switchgear room would ue available during a postulated main steam line break accident in the turbine building.
However, with bearing cooling water supplied to the NA-1 chillers instead of service water, the reliability of tne NA-1 chillers is called into question because bearing cooling is not safety-related.
Bearing cooling would not be available in the event of a loss of offsite power event or design basis earthquake coincident with the main steam linc break accident in the turbine building.
Therefore, an exemption from 10 CFR 50.49 for the NA-2 chillers is l
requested for the period that the service water system is isolated from the NA-1 recirculation spray heat exchangers and the control room chillers.
While the shutdown unit's Technical Specifications (TS) do not require the air conditioning systems to remain operable in Modes 5 and 6, the environmental qualification design basis for tbe operating unit's air conditioning systems requires at least one of the shutdown unit's chillers to be operable as a backup to the operating unit.
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The accident of concern results in an environmental condition in the NA-2 chiller room for which the NA-2 control room chillers are not qualified and may cease to function properly.
The or.ly postulated accident event that could cause this condition is the failure of a main steam line in the turbine bui' ding basement in proximity to the NA-2 chiller room. However, in order to have sufficient steam concentration in the area to disable the NA-2 chillers, the main steam trip valve on the line would also have to fail to a closed position.
This is unlikely because the trip valves are essentially check valves reversed to the flow of steam with the che '. oisk physically held out of the steam flow path.
Failure to hold the disk out of the steam flow path would cause the trip valve to slam shut.
Failure of the valve where the disk is stuck open is, therefore, highly unlikely.
The Need for the Procosed Action:
The proposed exemption is needed in order to permit the completion of highly desirable repairs and replacement activities in the NA Service Water
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System (SWS) without unduly extending the next several scheduled NA-l&2 refueling outages.
Environmental Imoacts of the Procosed Action:
The proposed exemption does not involve any measurable environmental impacts during normal operation since the plant configuration is changed only minimally and operation of NA-2 is not changed. The likelihood of the above accident scenario during the time the exemption would be in effect is low.
Thus, the proposeo exemption vauld not significantly affect the probability or consequences of potential reactor accidents and would not otherwise affect I
l l radiological plant effluents.
Consequently, the Commission concludes that there are no significant radiological impacts associated with the proposed exemption.
With regard to potential non-radiological impacts, the proposed exemption involves features located entirely within the restricted area as defined in 10 CFR Part 20.
It does not affect non-radiological plant effluents and has no other environmental impact.
Therefore, the staff concludes that there are no significant non-radiological environmental impacts associated with the proposed exemption.
Alternatives to the Proposea Action:
Since the staff has concluded that there are no measurable environmental impacts associated with the proposed exemption, any alternatives with equal or greater environmental impact need not be evaluated. The principal alternative to the exemption would be to require strict compliance with 10 CFR 50.49.
Such action would not significantiv enhance the protection of the environment, and would result in a significa
.oss of power to the licensee, as the next two refueling outages would have to be extended considerably.
Alternative Use of Resources:
This action does not involve the use of any resources not previously considered in the Final Environmental Statement for the North Anna Power Station, Units No. 1 & No. 2.
Acencies and Persons Consulted:
The NRC staff reviewed the licensee's request and did not consult other agencies or persons.
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' FINDING OF NO SIGNIFICANT IMPACT Based upon the foregoing environmental assessment, the staff concludes that the proposed action would not have a significant effect on the quality of the human environment and has determined, therefore, not to prepare an environmental impact statement for the proposed exemption.
For further details with respect to this action, see the application diLed September 11, 1992, which is available for public inspection at the Commission's Public Document Room, The Gelman Building, 9120 L Street, NW.,
Washington, DC 20555, and at the local public document room locc+ad at the Alderman Library, Special Collections Department, University of Virginia, Charlottesville, Virginia 22903-2498.
Dated at Rockville, Maryland, this 20th day of November 1992.
FOR THE NUCLEAR REGULATORY COMMISSION RCl Bart C. Buckley, Acting %
g.
Director Project Directorate 11-2 Division of Reactor Projects - 1/II Office of Nuclear Reactor Regulation I