ML20129A749
| ML20129A749 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 07/02/1985 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20129A712 | List: |
| References | |
| NUDOCS 8507150376 | |
| Download: ML20129A749 (3) | |
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UNITED STATES
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g NUCLEAR REGULATORY COMMISSION
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- j WASHINGTON, D. C. 20555
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SAFETY EVALUATION AMENDMENT NOS. 48 AND 14 TO NPF-14 AND NPF-22 SUSQUEHANNA STEAM ELECTRIC STATION, UNITS 1 AND 2 DOCKET NOS. 50-387/388 Introduction The licensee has provided proposed changes to both the Unit 1 and Unit 2 Technical Specifications. The proposed changes improve the availability of the ECCS system for design basis accidents by including controls in the Technical Specifications on equipment which must be OPERABLE to ensure proper functioning of the isolated 480 volt swing busses.
Evaluation Each unit has two redundant 480 volt swing busses and each 480 volt swing bus has two power supplies, preferred and alternate. The two redundant busses in each unit support the operation of the LPCI injection valve motor operators, recirculation loop bypass valve motor operators, ana recirculation discharge valve motor operators. The preferred power source to each bus is supplied through the MG set, which is used to electrically isolate two redundant load groups. Faults on a swing bus would not be propagated into more than one load group. The automatic transfer switch transfers the swing bus to the alternate power source upon loss of voltage; however, if the undervoltage is caused by a fault at the swing bus, automatic transfer will be prevented. When voltage is restored, on the preferred source, the swing bus will be automatically transferred back to the preferred source. The FSAR design basis for the system (FSAR 8.3.1.3.5) provides the basis as the following:
"The swing bus and transfe: switch are designated so that for a loss of offsite power and any single failure, the minimum required ECCS flow to meet 10 CFR 50 Appendix K criteria is always available."
Hcwever, the current LCO in the technical specification covers the swing busses and their associated transfer switches but it does not cover the MG sets for the following postulated event. Swing bus MG set "A" is down for maintenance with no LC0 to force its return to service. A break occurs in the "B" recirculation loop together with a single failure of the alternate pcwer source, Channel C 4 kV power supply; this renders both LPCI loops inoperable. The "B" loop is out of service due to the break, and the "A" loop injection valve is without power to open.
8507150376 850702 PDR ADOCK 05000387 P
. FSAR 6.3.1.1.2 states the following:
In the event of a break in a pipe that is a part of the ECCS, no single active component failure in the ECCS prevents automatic initiation and successful operation of less than the following combination of ECCS equipment:
a.
2 LPCI umps (1 loop), 1 CS loop and the ADS or HPCI (i.e., CS failure ; or b.
1 LPCI pump, 1 CS loop and the ADS or HPCI (i.e., single diesel generatorfailure);or c.
2 LPCI pumps (1 loop), 2 CS loops and the ADS (i.e. HPCI failure)
In the FSAR these are the three minimum ECCS combinations which result after assuming the failures and assuming that the ECCS line break disables a LPCI system loop. Each of these combinations requires at least one LPCI pump with a flow path; no LPCI is available in the above postulated event. FSAR Table 6.3-5 outlines the various ECCS complements remaining after four assumed single failures. For the LPCI injection valve failure during a discharge pipe break, two core spray (CS) subsystems (i.e. four pumps) are assumed available. Only three CS pumps are available in the postulated event, due to the loss of the Channel C power as can be seen in Figure A of the licensee's October 1,1984 submittal. Therefore, the postulated single failure represents a potential unreviewed safety question if appropriate controls are not placed on the power sources supporting the isolated 480 volt swing bus.
Therefore, the ECCS - Operating Technical Specification should be written so the ACTION is required when the ECCS system operability has degraded to the point where a single failure will place the unit in an unanalyzed event.
Due to the relationship between the low pressure ECCS and the swing bus as evaluated, the ACTION time (LCO) associated with LPCI and CS was proposed for the swing bus support equipment including the MG set when it has reached the same condition.
Baseo on our evaluation of the relationship of the ECCS system to the swing bus for the postulated event and bases for the ACTION, the staff has concluced that the Technical Specification proposed for the swing busses, associated transfer switches and MG set is consistent with the operability requirements of the safety-related ECCS system and, therefore, is acceptable.
Environmental Consideration These amendments involve a change in the installation or use of a facility component located within the restricted area defined in 10 CFR Part 20.
The staff has determined that the amendments involve 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 the individual or cumulative occupational radiation exposure. The Connission has previously issued a proposed finding that these amendrants involve no significant hazards consideration and there has been no public
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. comment on such findings. Accordingly, these amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(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 these amendments.
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 these amendments will not be inimical to the common defense and security or to the health and safety of the public.
Dated: Jul 0 21985 l
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