ML20210T225
| ML20210T225 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 09/04/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20210T222 | List: |
| References | |
| NUDOCS 9709150017 | |
| Download: ML20210T225 (6) | |
Text
M ito y
4 UNITED STATES j
NUCLEAR REGULATORY COMMISSION I &
WASHINGTON, D.C. 306M-0001 s
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 105 TO FACILITY OPERATING LICENSE NO. NPF-51 ARIZONA PUBLIC SERVICE COMPANY. ET AL.
PALO VERDE NUCLEAR GENERATING STATION. UNIT NO. 2 DOCKET NO. STN 50-529
1.0 INTRODUCTION
By letter dated August 28. 1997, as supplemented by letter dated September 3.
1997, the Arizona Public Service Company (APS or the licensee) requested changes to the Technical Specifications (Appendix A to Facility Operating License No. NPF-51) for the Palo Verde Nuclear Generating Station (PVNGS).
Unit 2.
The Arizona Public Service Company submitted this recuest on behalf of itself, the Salt River Project Agricultural -Improvement anc Power District, i
Southern California Edison. Company. El Paso Electric Company. Public Service Company of New Mexico. Los Angeles De)artment of Water and Power, and Southern California Public Power Authority. Tie proposed changes would revise Technical Specification (TS) Table 4.3-2 to allow for a one-time, five-day extenr.on of the required surveillance interval for the main steam isolation system (MSIS) portion of the engineered safety feature actuation system (ESFAS) logic.
2.0 EVALUATION The proposed TS amendment would increase the surveillance interval on a one-time basis for the ESFAS MSIS instrumentation surveillance requirement of
-TS 4.3.2.1.
Specifically, the quarterly CHANNEL FUNCTIONAL TEST requirements of Table 4.3-2. " Engineered Safety Features Actuation System Instrumentation Surveillance Requirements." items 1. 2 and 3 of IV.B. "ESFA System Logic " and
' item IV.C. " Automatic Actuation Logic." would be extended for five days beyond the 25 percent extension of the surveillance interval allowed by TS 4.0.2.
The surveillance tests ccnnot be performed because there is a degraded contact block on the control room manual ISIS switch for Channel C which could cause a spurious trip input to the MSIS initiation logic. Spurious actuation of this switch during the performance of the quarterly MSIS channel functional tests may cause an inadvertent MSIS signal and result in tripaing the unit. The quarterly-surveillances are due September 4.1997, whic1 includes the maximum extension of 25 percent allowed by TS 4.0.2.
A five day surveillance extension would allow the unit to begin a controlled shut down for the scheduled refueling outage on September 6, 1997, and proceed to Mode 5 by September 9. 1997, where the surveillance is not required.
The switch will be replaced after the unit enters Mode 5 and tested prior to unit startup.
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- Although APS has replaced these switches on-line before, this evolution is considered to be high risk due to the physical location of the switch and the close proximity to other ESFAS channels and reactor protection system channels.
By letter dated September 3.1997. APS provided the results of a historical review of the performance of the switches.
The historical review spanned the last three years of Licensee Event Reports. Condition / Disposition Requests and Equipment Failure Data Trending. The review concluded that there have been no failures of the matrix logic, initiation logic, automatic actuation logic, or manual actuation that would have prevented the ESFAS MSIS from performing its design function.
As such, delayv.g the surveillance by five days is not expected to miss the identification of a condition that would result in the inability of the equipment to perform its intended function.
Further, in July, 1994, the TS surveillance intervals for the MSIS CHANNEL FUNCTIONAL TEST were increased from monthly to quarterly.
Probabilistic risk analysis techniques were used to demonstrate that the proposed surveillance interval extensions to quarterly did not result in increased risk when compared to the monthly surveillance interval.
Specifically, the studies found that the decrease in core melt fre test-induced transients is 8.78 x 10(-8)quency due to the reduced exposure to per year while the increase in core melt frequency due to the increase in system unavailability is less than 6.3 x 10(-8) per year. Therefore, the net impact of increasing the surveillance interval from 30 da the overall core melt frequency.ys to 90 days resulted in a slight decrease in The increase in the surveillance test interval that is being requested by this TS amendment request is five days beyond the 25 percent extension of the interval. Given the results of the probabilistic risk analysis discussed above, where the overall core damage frequency would actually decrease for longer test intervals in this range, the re negligible effect on core damage frequency. quested extension would have a Based on the above, the staff concludes that the one-time, five-day extension of the quarterly surveillance interval beyond the 25 3ercent extension for the channel functional test for the ESFAS MSIS is accepta)le.
3.0 DESCRIPTION
OF EXIGENT CIRCUMSTANCES The degradation of the Channel C marual MSIS switch was identified by the licensee on August 14. 1997, when a spurious trip of MSIS leg 1-3 initiation logic occurred. Subsequent troubleshooting determined that a higher than normal voltage drop exists across the switch, making it highly susceptible to spurious operation. As a result, the licensee concluded that the surveillance tests in TS Table 4.3-2 for the MSIS logic cannot be performed because the degraded control room manual MSIS switch for Channel C could cause a spurious trip input to the MSIS initiation logic. Spurious actuation of this switch during the performance of the quarterly MSIS channel functional tests required by TS Table 4.3-2 may cause an inadvertent MSIS signal and result in tripping the unit. The quarterly surveillances are due September 4,1997, which a
- includes the maximum extension of 25 percent allowed by TS 4.0.2.
A five-day surveillance extension would allow the Unit to begin a controlled shut down for the scheduled refueling outage on September 6. 1997, and by September 9, 1997, where the surveillance is not required. proceed to Mode 5 The switch will be replaced after the unit enters Mode 5 and tested prior to unit startup.
Although APS has re) laced these switches ~on-line before. this evolution is considered high risc due to the physical location of the switch and the close aroximity to other ESFAS channels and reactor protection system channels. APS 1as determined that the risk associated with switch replacement outweighs the risk associated with increasing the allowed surveillance interval by five days.
The exigent situation exists and cannot be avoided because (1) the degraded condition of the MSIS manual switch did not occur until August 14. 1997, and could not have been aredicted. (2) performance of the ESFAS logic channel functional tests wit 1 the degraded switch could cause an inadvertent MSIS (and a resulting plant trip), and (3) the quarterly surveillance requirements cannot be extended beyond September 4. 1997, without exceeding TSs 3.3.2 and l-4.0.2 periodicity requirements which would require entering TS 3.0.3 Action Statements to shut down the unit.
The staff finds the licensee acted in a timely manner and there was not sufficient time to process this amendment request in the rout 1m manner as described in 10 CFR 50.91 without causing an unnecessary shutdown.
4.0 FINAL N0 SIGNIFICANT HAZARDS CONSIDERATION DETERMINATION The Commission has made a final determination that the amendment involves no significant hazards consideration.
Under the Comission's regulations in 10 CFR 50.92(c). this means that operation of the facility in accordance with the proposed amendment would not (1) involve a significant increase in the probability or consequences of an accident previously evaluated: or (2) create the possibility of a new or different kind of accident from any accident previously evaluated; or (3) involve a significant reduction in a margin of safety.
The staff-has evaluated the proposed changes against the above standards as required by 10 CFR 50.91(a) and has concluded that:
1.
The proposed change does not involve a significant increase in the probability or consequences of any accident previously evaluated.
The proposed amendment would increase the surveillance interval on a one-time basis for the ESFAS MSIS instrumentation surveillance requirement of TS 4.3.2.1.
Specifically, the quarterly CHANNEL FUNCTIONAL TEST requirements of Table 4.3-2. " Engineered Safety Features Actuation System Instrumentation Surveillance
4 Requirements." items 1. 2 and 3 of IV.B. "ESFA System Logic " and IV.C. " Automatic Actuation Logic." would be extended for five days beyond the 25 percent extension of the surveillance interval allowed by TS 4.0.2.
Increasing the surveillance interval does not constitute a physical change to the unit or make changes in the setsoints, system logic or manual actuation.
In addition, this clange does not alter physical plant equipment or the way in which plant equipment is operated. Therefore it does not involve a significant increase in the probability or consequences of an accident previously evaluated.
The ESFAS is designed such that a single failure in the system will not prevent actuation of the system.if required to do so.
The manual initiation logic is designed in a selective two out of-four arrangement.
Either Channel A or C will actuate leg 1-3 of the initiation logic.
Either Channel B or D will actuate leg 2-4 of the initiation logic. When both legs have been actuated, then the a1propriate signc1 will be generated, a MSIS in this case.
The C1annel C manual MSIS handswitch is still capable of performing its intended function - actuating MSIS leg 1-3 initiation logic. Therefore, the system may sustain a single failure and still be capable of performing its intended safety function of mitigating certain design basis events.
Since the system actuation capability has not been changed by the requested surveillance interval extension, the croposed TS amendment does not involve a significant increase in'the probability or consequences of an accident previously evaluated.
2.
The proposed change does not create the possibility of a new or different kind of accident from any accident previously evaluated.
The proposed amendment would increase the surveillance interval on a one-time basis for the ESFAS MSIS instrumentation surveillance requirement of 4.3.2.1.
Specifically, the quarterly CHANNEL FUNCTIONAL TEST requirements of Table 4.3-2. " Engineered Safety Features Actuation System Instrumentation Surveillance Requireneents." items 1. 2. and 3 of IV.B. "ESFA System Logic " and IV.C " Automatic Actuation Logic " would be extended for five days beyond the 25 percent extension of the surveillance interval allowed by TS 4.0.2.
The proposed one-time surveillance interval extension does not introduce any new modes of plant operation or new accident precursors.
No physical alterations to plant configurations or changes to system setpoints or logic are proposed by this request.
The proposed TS amendment is requesting a one-time extension of the quarterly surveillance interval for the MSIS system logic and does not represent any activity which could initiate a new or different kind of accident.
No new failure modes have been
j defined, nor any new system interactioris introduced for any plant system or component.
In addition, no new limiting failure has been identified as a result of the proposed change.
The ESFAS MSIS system logic remains the same and is capable of performing its design function. Therefore, the proposed TS amendment does not create the possibility of a new or different kind of accident from any accident previously evaluated.
3.
The proposed change does not involve a significant reduction in a margin of safety.
The proposed amendment would increase the surveillance interval on a one-time basis for the ESFAS MSIS instrumentation surveillance requirement of 4.3.2.1.
Specifically, the quarterly CHANNEL FUNCTIONAL TEST requirements of Table 4.3-2 " Engineered Safety Features Actuation System Instrumentation Surveillance Requirements." items 1. 2 and 3 of IV.B. "ESFA System Logic " and IV.C. " Automatic Actuation Logic." would be extended for five days beyond the 25 percent extension of the surveillance interval allowed by TS 4.0.2.
Under the proposed TS amendment, the ESFAS MSIS instrumentation, including the manual tri their safety functions. p switches, remain capable of performing The proposed TS amendment does not affect the design or performance of the ESFAS MSIS logic. As such the response of the MSIS actuation instrumentation would not change and, therefore, there would be no change in analyzed accident scenarios and/or outcomes.
Therefore, the proposed change does not involve a significant reduction in a margin of safety.
Accordingly, the Commission has determined that this amendment involves no significant hazards consideration.
5.0 STATE CONSULTATION
In accordance with the Comission's regulations, the Arizona State official was notified of the proposed issuance of the amendments.
The State official had no comments.
6.0 ENVIRONMENTAL CONSIDERATION
The amendment changes surveillance requirements.
The NRC staff has determined that the amendment involves 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 si occupational radiation exposure.gnificant increase in individual or cumulative The Commission has made a final no significant hazards consideration determination with respect to this amendment. Acco-dingly. the amendment meets the eligibility criteria for categorical exciusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR
o - 51.22(b)-no environmental impact statement.or environmental assessment need be prepared in connection with the issuance of the amendment,
7.0 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:
K. Thomas Date:
September 4, 1997 4
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