ML20057C356
| ML20057C356 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 09/17/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20057C355 | List: |
| References | |
| NUDOCS 9309280262 | |
| Download: ML20057C356 (3) | |
Text
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l SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 83 TO FACILITY OPERATING LICENSE NO. DPR-80 AND AMENDMENT NO. 82 TO FACILITY OPERATING LICENSE NO. DPR-82 PACIFIC GAS AND ELECTRIC COMPANY DIABLO CANYON NUCLEAR p0WER PLANT. UNITS 1 AND 2 DOCKET N05. 50-275 AND 50-323
1.0 BACKGROUND
By letter dated December 24, 1992, Pacific Gas and Electric Company (PG&E) proposed to amend Facility Operating Licenses DPR-80 and DPR-82.
The amendment would remove from the subject technical specification (TS) all references to supplemental vital inverters and supplemental vital busses for Units 1 and 2 cycle 7 and after.
PG&E intends to install new uninterruptible power supplies (UPSs) in March and September 1994 for Units 1 and 2, respectively.
For Units 1 and 2 cycle 6 the references to the existing six UPSs will remain in the subject TS. As a result of this equipment change, Diablo Canyon Units 1 and 2 will no longer have supplemental vital inverters.
Vital inverters convert dc power to 120 V ac as part of the UPSs that supply power to vital ac distribution panels.
PG&E proposes to replace the existing six UPSs with four larger UPSs.
Additional regulating transformers and transfer switches will provide increased redundancy to the UPSs.
Currently, vital instrument ac power is supplied by four 120-V vital instrument ac buses and two 120-V supplemental vital instrument ac buses, each energized from its associated inverter. The six inverters are each rated at 7.5 kVA.
These inverters are to be replaced by four inverters rated at 20 kVA each. The increase in capacity is needed to power future instrument systems loads. All six existing inverters share one voltage regulator as a backup power supply.
With the new configuration, each inverter will have its own regulating backup transformer, which could be connected to either the normal 480-V at vital bus or an alternative 480-V ac vital bus.
Each of the four new Class lE UPSs will contain a regulating rectifier, inverter, static bypass switch, and manual bypass switch. An auctioneer will automatically select the higher of the two de sources. The preferred source for each inverter normally will be the rectified 480 V ac power from the vital bus.
Each new UPS will contain a static transfer l
switch that will automatically transfer the 120-V ac vital loads to the new dedicated regulating transformer fed by the associated 480-V ac vital bus if the inverter or its sources should fail.
In addition, each regulating l
transformer will be connected to a manual transfer switch that will let the i
transformer be connected to its alternative 480-V ac vital bus if the normal 9309280262 930917 PDR ADOCK 05000275 i
P PDR
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480-V ac vital bus should fail. Thus, multiple failures would be needed to interrupt the UPS output to the 120-V ac vital loads for longer intervals than required to switch from one source to another.
j 2.0 fyALUATION The proposed new equipment will be installed in accordance with applicable l
codes and standards to upgrade plant equipment reliability, capacity, and 4
flexibility. The six 7.5-kVA inverters (45 kVA total) will be replaced by four new inverters (80 kVA total) to increase load capacity and provide automatic load transfer functions. The addition of new static transfer switches and dedicated bypass voltage regulating transformers will improve power availability in the event of a single equipment failure.
By preserving the independence of the four UPSs and of their vital instrument ac panels, the new design continues the reliability of the existing design because of its redundancy. The four UPSs will each be supplied by a plant battery that will be connectible to either of two chargers which, in turn, will be connected to' different 480-V ac vital buses.
Because of the increased capability of the inverters and the increased number of power supplies to the UPS, either by rectification or directly by means of new transformers and switches, there is no significant increase in the probability of occurrence of an accident previously evaluated; a decrease is more probable.
Previous analysis assumed a loss of one division of onsite power distribution (one vital inverter and one supplemental inverter); therefore, the consolidation of the vital and supplemental inverters does not alter the basis of the previous analysis. The new UPSs will improve the capability of the onsite power distribution system to fulfill its safety-related function to provide an uninterrupted supply of 120-V ac power required for plant safety.
The new equipment will be qualified and installed to applicable codes and standards, and operated within the requirements of the limiting conditions for operation (LCO) specified in the proposed TS. These LC0 restrictions are the same as those in the existing TS. Therefore, the proposed changes do not create the possibility of a new kind of accident or one that is different from any accident previously evaluated. Nor do the proposed changes involve a significant reduction in any margin of safety.
The staff has evaluated the proposed vital inverter equipment changes, and as requested by the licensee in its letter of December 24, 1992, it has reviewed the wording changes of the associated TS. The staff concludes that the licensee has provided adequate justification for these changes and the changes are therefore acceptable.
3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the California State official was notified of the proposed issuance of the amendments. The State official had no comments.
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4.0 ENVIRONMENTAL CONSIDERATION
These amendments change 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 NRC 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 individual or cumulative occupational radiation exposure.
The Commission has previously issued a proposed finding that the amendments involve no significant hazards considera-tion, and there has been no public comment on such finding-(58 FR 8775). Accordingly, the 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 the amendments.
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 amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
C. Morris i
I Date: September 17, 1993 I
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