ML20151N470
| ML20151N470 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 07/28/1988 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20151N468 | List: |
| References | |
| NUDOCS 8808090009 | |
| Download: ML20151N470 (3) | |
Text
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UNITED STATES o%
NUCLEAR REGULATORY COMMISSION
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WASHINGTON, D. C. 20555 4
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION ILLIN0IS POWER COMPANY CLINTON POWER STATION D0CKET N0. 50-461
1.0 INTRODUCTION
By letter dated June 2, 1988 Illinois Power Company submitted a request for a revision to their position concerning the Nuclear Systems Protection System (NSPS) Self-Test System (STS) Failure Detection and Indication for the Clinton Power Station. The ccmitment concerns a condition discovered in which the annunciator features of the STS were not functioning as described in an earlier supplement (No. 2) of the Clinton SER.
The STS is an automatic testing system that injects short duration pulses into the solid state NSPS circuits and verifies proper response to various input combinations. The STS is designed to maintain surveillance over NSPS cabinet circuitry essential to reactor protection, emergency core cooling and safe shutdown of the reactor. The STS is an overlay testing and surveillance subsystem that provides the capability to continuously and automatically perform testing of the circuitry within the NSPS panels. The primary purpose of the STS is to improve the availability of the NSPS by optimizing the time to detect and determine the location of a failure in the system.
Supplement 2 of the Clinton SER documented the staff's acceptance of the licensee's STS. The staff noted that the automatic testing performed by the STS offers advantages over conventional surveillance test methods. The supplement included a description of the annunciator features of the STS and described how if a failure was detected in any of the four divisions of functional logic tested by the STS, one of several annunciators intended to identify the affected division would be actuated in addition to the "STS utilized by operators and technicians (using the plant computer) gram could be Detected Failure" alarm.
It also described how a diagnostic pro to determine the location of a detected failure to the printed-circuit (PC) card level.
It was discovered that, due to the STS as-built design and the way in which the STS automatic test sequence is executed between divisions, the correct division innunciators were not always actuated for the division in which a fault was detected. The licensee committed to implement a plant modification for correcting the annunciator condition.
In Supplement 6 to the Clinton SER, the staff acknowledged the annunciator problem, stipulating that it would be acceptable to disable the division annunciators and to allow the STS to continue to operate without the extra h80 MOCK 03000461 009 880728 P
r annunciators on an interim basis until implerentation of the annunciator modification prior to startup after the first refueling outage. The interim means of operation was determined to be acceptable since the "STS Detected Failure" annunciator would remain operable and operators and technicians can use the diagnostic program to locate faults to the PC card level (and thus determine the affected system and division.)
Although operation of STS without the use of the division annunciators was stipulated to be an interim means of operation, the licensee states that experience to date has confirmed that these annunciators are not needed and that the interim means of operation is acceptable on a permanent basis. The licensee bases this on the fact that when the "STS Detected Failure" alarm is actuated, operators and technicians must utilize the diagnostic program to identify a fault to the PC card level regardless of the state or status of the division annunciators.
Identification of a fault to the PC card level is required in order to repair the fault and take appropriate action. Once a fault is identified to the PC card level, the affected systcm and division will also have been identified. The division annunciators therefore provide no extra information that is immediately useful.
The licensee therefore desires to close this open issue with no modification required.
2.0 EVALUATION The NSPS contains circuitry essential to reactor protection, emergency core cooling, and safe shutdown of the reactor.
It takes approximately 1 to 2 minutes to diagnose each one of the three divisions that does not have a fault and approximately 15 minutes to diagnose a division that has a fault. Therefore the maximum amount of time to diagnose the entire NSPS to the PC card level is l
approximately 20 to 25 minutes.
There are a total of five annunciators related to the STS failure detection in t
the control room.
The licensee plans to only use the "STS Detected Failure" annunciator and abandon the four division annunciators. The original design included 15 minutes to diagnose a failure to the PC card level. The proposed l
design will increase the diagnosis time by a maximum of 10 minutes.
l l
The STS design and use of the diagnostic program to identify specific fault locations, remains one of the fastest methods of detecting faults within protection system circuits at connercial nuclear power reactors. The STS will be totally functional in accordance with the Clinton Technical Specifications, and all STS detected failures will be alanned by the "STS Detected Failure" l
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3.0 CONCLUSION
l Based on the above evaluation, the staff concludes that the licensee's request to operate the STS in the above described manner is acceptable.
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0 The staff has concluded 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 Comission's regulations, and is acceptable to the staff.
Principal Contributor: B.Marcus,(SICB/ DEST)
Dated:
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