ML17306B228
| ML17306B228 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 01/04/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17306B227 | List: |
| References | |
| NUDOCS 9301070029 | |
| Download: ML17306B228 (6) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555 SUPPLEMENTAL SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION STATION BLACKOUT RULE 10 CFR 50.63 ARIZONA PUBLIC SERVICE COMPANY PALO VERDE NUCLEAR GENERATING STATION UNITS 1
2 AND 3 DOCKET NOS.
50-528 529 AND 50-530
1.0 INTRODUCTION
The NRC staff's Supplemental Safety Evaluation (SSE) pertaining to the Arizona Public Service Company's (the licensee's) responses to the Station Blackout (SBO) Rule, 10 CFR 50.63, was transmitted to the licensee by letter dated July 28, 1992.
The staff's SSE found the licensee's proposed method of coping with an SBO to be acceptable except that the 3-month interval operability tests of the gas turbine generators (the AAC power source) should include testing the gas turbine generators (GTGs) under load.
The licensee provided a response to the staff's SSE by letter from W. F.
- Conway, dated October 2, 1992.
By enclosure to the letter, the licensee concluded that the 3-month tests, under load, were not required by the SBO Rule guidance and are not appropriate.
The staff's evaluation of the licensee's response follows.
2.0 EVALUATION
- 2. 1 Licensee Res onse The licensee's response references NUMARC 87-00, Item B. 10, which states that the Alternate AC (AAC) source shall'e started and brought to operating conditions that are consistent with its function as an AAC source.
The licensee states that it does not interpret this to require loading the AAC, only that the AAC should be energized to verify that it can meet its intended operability and reliability.
- Further, the licensee contacted NUMARC and NUMARC concurred stating that the intent was to bring the AAC power source to operating conditions (voltage and frequency).
The licensee states that the GTGs feed the 13.8 kV buses downstream of the start-up transformers and upstream of the Class lE buses.
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loading of the GTGs would require paralleling them with the 13.8 kV power sources.
The licensee states that the GTGs were not designed to operate in parallel with an energized unit during power operation.
The GTGs are located outside the protected area, with the controls and indication in a local control room near the GTGs.
The design does not include GTG controls or indication in the main control rooms.
The licensee states that any paralleling evolution creates the potential for transients caused by equipment malfunction and human error.
Operator actions remote from the main control room increases the potential for error.
- Also, a
deenergization of a 13.8 kV bus from the offsite source during power operation would result in a Technical Specification (TS) Limiting Condition for Operation (LCO) action statement, including a start of the diesel generator.
The licensee proposes to load test the GTGs during refueling outages that have a Train A 13.8 kV electrical bus scheduled for maintenance.
These outages would occur approximately once every 12 months.
The tests would include a
timed start (within the I-hour time frame) and operation of each GTG in parallel with the offsite source (which is feeding the emergency buses) at rated load until stable operating parameters are achieved.
2.2 Staff Evaluation The staff agrees with the licensee that the intent of the 3-month tests are to demonstrate the operability and reliability of the AAC source to perform its intended function.
However, the intended function of the AAC source is to power the SBO loads.
The staff does not interpret this to mean that the actual SBO loads need be powered on a 3-month basis, provided the ability to power these loads is demonstrated initially and every refueling outage.
Powering an equivalent load on a 3-month basis should be sufficient to demonstrate the reliability of the AAC source.
The staff recognizes that paralleling a
GTG with the normal AC power source creates some potential for introducing a transient.
However, the staff believes that the 3-month load tests are necessary to obtain sufficient data to demonstrate the required 95X reliability of the GTGs.
Therefore, the licensee should conduct the 3-month load tests or describe what other means it intends to demonstrate that a 95X reliability is being maintained.
3.0
SUMMARY
AND CONCLUSION The staff has reviewed the licensee's October 2,
- 1992, response to the staff's July 28,
- 1992, supplemental safety evaluation pertaining to the licensee's proposed plan for implementing the Station Blackout Rule.
The staff concludes that the licensee should implement the 3-month load tests of the proposed
t AAC power source (the gas turbine generators) in accordance with NUHARC 87-00, Item B-IO, or describe what other means it intends to demonstrate that a 95X reliability is being maintained.
Principal Contributor:
Argil Toalston Electrical Engineering
- Branch, NRR Date:
January 4,
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