ML20056E793

Special Rept:On 930721 & 0803,valid Test Failures of Div I DG Occurred Due to Problem W/Contacts within Breaker Control Switch & Failed Coil in B-C Phase Undervoltage Relay, Respectively.Subj Parts Will Be Replaced During DG Outage

ML20056E793
Person / Time
Site:	Clinton
Issue date:	08/20/1993
From:	Phares R ILLINOIS POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
U-602174, NUDOCS 9308250178
Download: ML20056E793 (5)

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ishnois Power Company Chnton Power Station P.o. Box 678 Chnton, IL 61727 Tet 217 935-8881 ILLIN 91S u.602 24 PCeWER M7 93(08-20)LP 8E.110c August 20,1993 Docket No. 50-461 10CFR50.36 Document Control Desk Nuclear Regulatory Commission Washington, D.C. 20555

Subject:

Special Report: Valid Test Failures of Division I Diesel Generator at Clinton Power Station (CPS)

Dear Sir:

Clinton Power Station (CPS) Technical Specification 4.8.1.1.3 requires all diesel generator failures, valid or non-valid, to be reponed to the NRC within 30 days pursuant to Specification 6.9.2, SPECIAL REPORTS. Due to valid failures of the Division I Diesel Generator (DGI A) during surveillance testing on July 21,1993 and on August 3,1993 the attached Special Report is being submitted in accordance with the CPS Technical Specifications to provide the information required by Regulatory Guide 1.108, Revision 1,

" Periodic Testing of Diesel Generator Units Used as Onsite Electric Power Systems at ,

Nuclear Power Plants," Regulatory Position C.3.b, for both failure events.

l Additionally, this letter provides an update to the progress of the investigation into the June 23,1993 failure previously identified as an invalid failure in Illinois Power's (IP's)

Special Report dated July 23,1993 (reference IP letter U-602163). The reverse power relay which lead to the failure was sent offsite for testing as pan of the corrective action plan reported in the July 23,1993 Special Report. Further evaluation of the testing results is being performed, and the results of this investigation will be provided in a follow-up letter to the NRC by September 24,1993. However, the results ofinitial investigations have shown that the failure experienced on June 23,1993 would have prevented the diesel generator from performing it's safety function. As a result, that failure should have been classified as a valid failure. This combined with the valid failures experienced on July 21, 1993 and August 3,1993 constitute seven valid failures in the last 100 valid tests of  !

DGIA. The additionalinformation recommended by Regulatory Guide 1.108 Regulatory Position C.3.b. (as required by Technical Specifications 4.8.1.1.3) will be provided in a 9308250178 930820 V

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Page 2 of 2 to U-602174 sdpplemental report by September 24,'1993 as discussed in a telephone conversation between R. F. Phares (IP) and R. L. Hague (NRC) conducted on August 20,1993.

Submittal of this letter and its attachment satisfies the requirements of CPS Technical Specifications 4.8.1.1.3 and 6.9.2 for submitting a Special Report for the July 21,1993 and August 3,1993 diesel generator failures.

Sincerely yours, l

Richard F. Phares Director-Licensing

CLJE/nis ,

Attachment l cc: NRC Clinton Licensing Project Manager NRC Resident Office, V-690  :

Regional Administrator, Region III, USNRC Illinois Department of Nuclear Safety 1

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Attachment I to U-602174 Page1of3 Special Report This Special Report addresses valid failures of the Division I Diesel Generator (DGI A) which occurred on July 21,1993 and August 3,1993. Specific information on each event is provided below.

Description of Event / Cause of Failure Valid Failure on July 21,1993 1 l

At 0452 hours0.00523 days <br />0.126 hours <br />7.473545e-4 weeks <br />1.71986e-4 months <br /> on July 21,1993, DGI A was started for surveillance per Clinton Power Station (CPS) Procedure 9080.13, " Diesel Generator l A (IB) Quick Start Operability " During this surveillance test, the DGI A cutput breaker failed to close when j the operator attempted to synchronize the generator with offsite power. A second attempt to synchronize DGI A was made but again the output breaker failed to close. DG1 A was declared inoperable, and the other two divisional diesel generators were verified OPERABLE in accordance with Technical Specifications.

Maintenance Work Request (MWR) D51984 was initiated to troubleshoot and identify the cause of failure of the output breaker to close. As part of the troubleshooting I process, the control panel for DGI A was thoroughly inspected and no discrepancies were discovered. Additionally, closing circuit components and connections from the control power fuses to the DGI A output breaker were thoroughly inspected and no abnormalities were found. As part of the troubleshooting process, additional recording instrumentation was installed in the circuitry of DGI A to record and examine control / relay signals during subsequent DGI A starting and loading attempts.

Initial troubleshooting did not reveal a cause for the DGI A failure. Subsequently, the diesel generator output breaker was racked back in and the diesel generator was tested six times with satisfactory results. During one of these runs, the DGI A output breaker "Sersice Not Available" annunciator (which indicates when the permissives for the breaker closure are not met) momentarily alarmed in the control room but did not prevent the DGIA from being successfully synchronized with its associated safety bus. As troubleshooting continued, the recording instrumentation connected to the diesel control circuitry confirmed that the closing circuit voltage signal from the manual breaker control

! switch (Electro-Switch Corporation Part #20KD-91254-21) in the main control room to l the diesel generator was momentarily interrupted (for less than a tenth of a second). Since this occurred in such a small time period, it has been concluded that operator error could

! not have caused the annunciator to alarm as DGI A was successfully synchronized. This

! could however indicate a problem with the contacts within the breaker control switch.

This is considered to be the most probable cause of the July 21,1993 valid failure. The control switch was unable to be replaced due to a lack of spare parts. In addition, this is a

Attachment 1 I to U-602174 Page 2 of 3 sealed switch which precludes cleaning of the individual contacts. The contacts in question are not active components except when placed in pull-to-lock position. The pull-to-lock position is only used when the DGl A is intentionally removed from service (e.g.

during maintenance). Due to the interruption only occurring during manipulation of the control switch, and the six successful runs of DGI A, reasonable assurance exists that the breaker (and/or control circuitry)is capable of performing its intended design function. In addition, verification that the DGI A output breaker "Sersice Not Available" annunciator is not illuminated provides continual assurance of automatic breaker operation capability due to circuit design. Therefore, on July 22,1993, at 2055 hours0.0238 days <br />0.571 hours <br />0.0034 weeks <br />7.819275e-4 months <br />, DGI A was declared OPERABLE. Test equipment and recording instrumentation continues to be utilized during each DGI A start to document if the noted annunciator a: arms during future runs.

' On August 16, 1993 during a weekly run of the DGI A, the "Sersice Not Available" annunciator alarmed again and the closing circuit voltage signal momentarily decreased as recorded on the installed recording instrumentation. This reoccurrence, which again occurred during manual operation of the DGl A output breaker control switch, funher supports the theory that the manual breaker control switch intermittently fails and that this is the most probable cause of the July 21,1993 valid failure of the DG1 A to synchronize with offsite power during surveillance testing. This failure is currently considered to be a valid failure pending the results of further investigations. Any new information gained as a result of further investigations will be provided in a follow-up letter by September 24,1993.

Valid Failure on August 3,1993 At 0550 hours0.00637 days <br />0.153 hours <br />9.093915e-4 weeks <br />2.09275e-4 months <br /> on August 3,1993, IP determined that an unrelated valid failure of DGIA had occurred. This valid failure was the result of a condition discovered during

, operational rounds by an area Operator. The DGI A B-C phase and A-B phase l undervoltage relays (Westinghouse model CV-2) were found with dropped targets which I

were unable to be reset. Failure of either of these relays, which are pan of the permissive-to-close circuitry for the DGlA output breaker, could cause closure of the breaker upon receipt of an automatic start signal coincident with a loss of offsite power. DGI A was declared inoperable since it may not have performed its safety function in the emergency

operating mode.

MWR D52716 was written to troubleshoot the problem. The cause of the undervoltage relay trip condition was attributed to a failed coil (the telephone coil) in the B-C phase undervoltage relay. A new CV-2 undervoltage relay was calibrated then installed in the B-C phase. DGIA was then successfully operated, including breaker closure, as part of the post-maintenance testing requirements. Based on completion of the operability surveillance and post-maintenance testing of the new B-C phase undervoltage relay, DG1 A was restored to OPERABLE status at 1730 hours0.02 days <br />0.481 hours <br />0.00286 weeks <br />6.58265e-4 months <br /> on August 3,1993.

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, Attachment 1 to U-602174 Page 3 of 3 Corrective Actions Valid Failure on July 21,1993 Although proper functioning of the DGIA output breaker was verified after the July 21,1993 failure as described above, five additional successful surveillance tests were completed providing further assurance that DGI A would perform as required. Additional l investigation into the valid failure on July 21,1993 is being conducted. Results from this investigation will be included in a follow-up letter by September 24,1993. IP is currently planning to replace the manual breaker control switch during the next scheduled DGIA outage which will occur during the second week in September 1993. Prior to the scheduled DGI A outage, the DGI A will continue to be run in accordance with the CPS i Technical Specifications and recording instrumentation will continued to be utilized during l each run in order to monitor breaker control switch performance. Corrective Actions for l DGI A will also be evaluated for applicability to the Division II and III diesel generators.

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! Valid Failure on August 3,1993 l

As a result of disassembly of the failed undervoltage relay, it was confirmed that the normally energized telephone coil had failed. The failure was subsequently determined

to be age related. As corrective action, the remaining comparable CV-2 relay associated with DGIA, as well as the two comparable relays associated with the Division II diesel i

, generator will be replaced during the next scheduled diesel generator outages. These relays are not used in a similar function for the Division III diesel generator. The remaining safety related relays that utilize telephone coils in similar configurations at CPS are normally de-energized. As a result, similar failures are not expected for these coils.

Test Intervals I

The July 21,1993 valid failure was the sixth valid failure in the last 100 valid tests i for DGlA, and the second valid failure in the last twenty valid tests for DGIA. The August 3,1993 valid failure was the seventh valid failure in the last 100 valid tests for DGIA, and the third valid failure in the last twenty valid tests for DGI A. Technical Specification Table 4.8.1.1.2-1 requires the testing frequency for a diesel generator to be l' increased from at least once per 31 days to at least once per seven days when the number of failures is greater than or equal to five in the last 100 valid tests or two in the last l twenty valid tests. Therefore, DGI A is, and will continue to be, tested on a weekly basis until seven consecutive failure-free demands have been performed and the number of failures is less than one in the last twenty valid tests.

l Technical Specification 4.8.1.1.3 also requires, if the number of failures in the last i

100 valid tests is seven or more, the additional information recommended in Regulatory l Guide 1.108 Regulatory Position C.3.b. be provided. This information will be provided in l a supplemental report by September 24,1993.

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