ML20082M691
| ML20082M691 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 04/17/1995 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20082M689 | List: |
| References | |
| NUDOCS 9504240342 | |
| Download: ML20082M691 (4) | |
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t UNITED STATES j
,j NUCLEAR REGULATORY COMMISSION t
WASHINGTON, D.C. 300eH001 1
i SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NOS. 73 AND 62 TO -
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FACILITY OPERATING LICENSE NOS. NPF-76 AND NPF-80 ffQ@lQ!LLIGHTING & POWER COMPANY f
CITY PUBLIC SERVICE BOARD OF SAN ANTONIO CENTRAL POWER AND LIGHT COMPANY l
f CITY OF AUSTIN. TEXAS DOCKET NOS. 50-498 AND 50-499 1
SOUTH TEXAS PROJECT. UNITS 1 AND 2 i
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1.0 INTRODUCTION
I By application dated November 8,1994, Houston Lighting & Power Company, et al., (the licensee) requested changes to the Technical Specifications (TSs)
(Appendix A to Facility Operating License Nos. NPF-76 and NPF-80) for the South Texas Project, Units 1 and 2 (STP). The proposed changes would require only one of the two battery chargers associated with each Class IE 125-VDC Channel.I and Channel IV to be operable, in TS 3/4.8.2.1, D.C.
Sources, Operating, and in TS 3/4.8.2.2, D.C. Sources, Shutdown.
i Subsequently, by letter dated March 14, 1995, the licensee withdrew that portion of the amendment request regarding TS 3/4.8.2.2, because the required wording was incorporated into this TS by Amendment Nos. 71 and 60, issued by the NRC on February 14, 1995, in response to another amendment request. The March 14, 1995, letter also provided clarifying information and did not change the initial no significant~ hazards consideration determination, j
t 2.0 EVALUATION The proposed changes would require only one of the two battery chargers associated with each Class IE 125-VDC Channel I and Channel IV to be operable.
The current TS 3.8.2.1 requires two battery chargers associated with Channel I i
and Channel IV to be operable during power operation. The proposed change will make TS 3.8.2 identical for all four Class IE 125-VDC channels.
9504240342 950417 DR ADOCK O 498 I
. The Class IE 125-VDC system at STP consists of four independent, physically separated channels (Channels I, II, III, IV), each served by two battery chargers and one battery.
Each battery supplies 125-VDC power required for plant protection and controls when power from normal AC power sources fails.
Each battery also supplies power to the associated inverters, which convert DC power to AC power for the vital instrumentation and control systems.
Each battery has sufficient capacity to supply its loads for 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />.
Each battery charger has sufficient capacity to restore the battery from its design minimum charge to its fully charged state while supplying normal and post-accident steady-state loads. The current limit setting of each battery charger is adjustable from 110 to 125 percent of the nominal rating and is presently set at 110 percent of the nominal setting, or 330 amperes.
During normal operation, the 125-VDC load is supplied from the battery chargers with the batteries floating on the system. Upon loss of offsite power, the entire load is powered from the batteries until the power is restored by the diesel generators (DGs).
Channels I and IV have a larger DC load and use a larger battery than Channels II and III. This load difference requires only one of the two operable battery chargers associated with Channels II or III, but requires two operable battery chargers associated with Channels I and IV.
The licensee is proposing to require only one instead of two battery chargers associated with Channels I and IV to be operable. This proposal is based on the recent evaluation of the DC load requirements for battery chargers for Channels I and IV.
The licensee states that requiring two battery chargers for Channels I and IV can potentially result in unnecessary and unplanned unit shutdowns as a result of the loss of a single battery charger.
The reason for the load difference between Channels I and IV and Channels II and III is a note in Updated Final Safety Analysis Report (UFSAR) Table 8.3-6, which imposes 393 amperes of load on Channels I and IV.
This value represents the maximum possible load that the batteries are capable of supporting while concurrently maintaining the required 2-hour duty cycle; however, this maximum possible load has been interpreted as the battery charger output current requirements. The licensee contends that this is not the correct battery charger load since this maximum load includes the inverters which are not powered from the battery or the battery charger if AC power is available.
When normal AC power is lost, power to the DC loads including the inverters is supplied by the batteries until the DG starts and loads. The motor control centers supplying the battery chargers and the inverters will then be sequenced onto the bus being supplied by the DG. Thus, the inverters do not become a load on the chargers unless normal AC supplies to the inverters or the rectifier portion of the inverters fail.
Therefore, one battery charger is sufficient to supply the necessary loads for Channel I or Channel IV.
The licensee has performed an analysis that identifies all of the actual Class lE 125-VDC loads for Channels I and IV for which the battery chargers may have to supply power, assuming the battery is fully charged. This analysis is conservative because it assumes the simultaneous failure of two inverters rated for 7.5 kilovolt amperes (kVA) and 25 kVA connected to Channels I and
'IV.
For this -analysis,, Channel I values (worst case) were used. The total-normal DC loads with batteries fully charged and the charger on normal float voltage is calculated to be 64 amperes. The current required by two inverters i
with batteries fully charged and the charger on normal float voltage is 216 amperes. These current requirements are based on 100 percent loading of both inverters.
Current conditions include minimum margins for future load growth of 21 percent for the 25-kVA inverter, 25 percent for the 7.5-kVA inverter, and 50 percent for the de loads.
The total current required by the two inverters with batteries fully charged, the charger on normal float voltage, and the normal DC bus loads is 280 amperes. Thus, a single battery charger using 110 percent (330 amperes) i current limit can maintain the Channel I or the Channel IV bus loads operable.
j Based on the above information, the staff finds that the analysis submitted by the licensee is conservative because the inverters do not become a load on the i
chargers unless an inverter failure occurs and that even with the loss of both inverters, a single battery charger is able to maintain the operability of i
Channel I or Channel IV at the design loading. Therefore, the staff finds the i
proposed revision to TS 3.8.2.1, to require only one battery charger to be operable for Channels I and IV instead of two, to be acceptable.
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3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Texas State official was notified of the proposed issuance of the amendments. The State official had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
The amendments change a requirement with respect to installation or use of a-facility component located within the restricted area as defined in 10 CFR Part 20. The NRC staff has determined that the amendments involve no i
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 Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (59 FR 63123). Accordingly, the amendment l
meets 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 i
environmental assessment need be prepared in connection with the issuance of the amendments.
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5.0 CONCLUSION
The Commission 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, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
- 0. Chopra Date: April 17, 1995 P
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