U-601788, Special Rept:On 910106,Div II Diesel Generator Failed During Test.Caused by Malfunction of A-3 Relay Tachometer. Preventive Maint Task Will Be Issued to Remove,Inspect & Bench Test A-3 Relay Every Two Yrs

Special Rept:On 910106,Div II Diesel Generator Failed During Test.Caused by Malfunction of A-3 Relay Tachometer. Preventive Maint Task Will Be Issued to Remove,Inspect & Bench Test A-3 Relay Every Two Yrs

ML20067C956
Person / Time
Site:	Clinton
Issue date:	02/05/1991
From:	Spangenberg F ILLINOIS POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
U-601788, NUDOCS 9102120267
Download: ML20067C956 (3)

Text

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'Cl ITION l'UWLH ST ATION. l' O. BOX 07b. rLtYf('N. ILL INOW 617'i 7 0676. 't1.Lti'llONt; G171105 hhh 1 February 5, 1991 Docket No. 50 461 Document Control Desk Nuclear Regulatory Conunission Washington, D.C. 20$$$

Subject:

Special Report: Test Pailure of Division II Diesel Generator at Clinton Power Stitt,lon (CPS)

Dear Sir:

CPS Technical Specification 4.8.1.1.3 requires all diesel generator failures, valid or non valid, be reported to the Nuclear Regulatory Commission (NRC) pursuant to Technical Specification 6.9.2, SPECIAL REPORTS, within thirty deys. Due to the valid failure of the Division II Diesel Generator (DC1B) during surveillance testing on January 6, 1991, this 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 Syst+ms at Nuclear Power Plants", Regulatory Position C.3.b.

Discriotton of Pvent At 0803 hours0.00929 days <br />0.223 hours <br />0.00133 weeks <br />3.055415e-4 months <br />, on January 6,1991, a start of DC1B was initiated in accordance with CPS Procedure 9080.01, " Diesel Generator 1A (IB) Operability - Manual". This test was being performed in accordance with Technical Specification 4.8.1.1.2.a. Thia Technical Specificatton requires that the diesel generator reach its frequency (speed) and voltage within twelve seconos af ter the initiation of a start signal. During this test it too: h.1 seconds for DG1B to reach the required speed of 60 1 1.2 Hertz (Hz). Voltage met the required 4160 1 420 volts within the required twelve seconds.

The initial assessment of the failure indicated a problem existed in the DGlB speed control electronics. Troubleshooting

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revealed that the A 3 relay tachometer (speed switch) experienced a malfunction. The A 3 relay directly feeds the engagement of the air start motors, main control room indication, and the diesel generator engine tachometer.

The A 3 relay failed due to a broken wire on one of the silicon control rectifiers. This resulted in an increased A-3 relay response time which delayed the response of all diesel generator control circuitry. Therefore, although adequate speed was reached, it was not reached within the time required by the Technical Specifications.

DG1B did meet the other acceptance criteria of surveillance 9080.01.

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Gudf44A}2LakCA7%# l The a J relay was replaced and surveillance 9080.01 was completed with satisfactory results at 0501 hours0.0058 days <br />0.139 hours <br />8.28373e-4 weeks <br />1.906305e-4 months <br /> on January 7,1991.

Since the plant wss in Mode 5 (REF'UELING), DG1B was not required to i be operable. The nature of the A 3 relay failure, the broken wire l inside the relay, was considered to be applicable to the Division I l Diesel Generator (DG1A); however, since the DG1A A 3 relay was replaced approximately one year ago, it is not considered susceptible to this failure. The Division III Diesel Generator control circuity was supplied by a different vendor than DG1A and DG1B and is not susceptible to this type of failure.

The most probable cause of the broken wire was aging of the A 3 relay combined with the stress placed on the wire during bench testing of the relay. This relay had been removed and calibrated in December 1990, to resolve problems experienced with the DG1B air j start solenoid valves. On January 6,1991 following reinstallation of the A 3 relay, the A 3 relay and DG1B vere verified to function by satisfactory performance of procedure 3506.01, " Diesel Generator and Support Systems." The next start of DG1B was on January 6, 1991 at which time DG1B failed to reach the required speed within twelve seconds,

.A preventive maintenance task (PM) will be issued to remove, inspect, and bench test the A 3 relay every two years to ensure the relay is functioning correctly and that wires and connections are intact. This PM will be initiated by May 31, 1991.

Additionally, a caution has been added to the vendor manual, the document governing bench testing of the A 3 relay, to ensure the electricians are aware of the susceptibility of the wires internal to the relay to be stressed and to break.

Test Intervala e

A total of seventy two tests, in accordance with Regulatory Guide 1.108 had been performed on DG1B as of January 6,1991. The January 6, 1991 was the fifth failure in the seventy two tests performed on DG1B and the second in the last twenty. Technical Specification Tabic 4.8.1.1.2 1, requires the testing frequency to be increased from at least once per 31 days to at least once per 7 days when the' number of failures is greater than or equal to two in the last twenty, or five in the last one hundred tests. DG1B was therefore tested on January 7,14, and 21,1991.

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On January 25, 1991, the NRC provided CPS with its evaluation of the DG failure classifications assigned as a result of finding inadequate shutdown service water (SX) flow to DG1A and DG1B on May 15, 1990. The NRC determined that the DG1B failure of May 15, 1990, was not a valid failure since D01B was not called upon to start.

This evaluation reduced the total number of tests to seventy one as of January 6,1991, and the valid number of failures to four ia.

seventy one and one in the last twenty. This decrease) the required testing frequency to at least once per 31 days.

This letter satisfies the requirement of CPS Technical Specifications 4.8.1.1.3 and 5.9.2 for issuing a SPECIAL REPORT for diesel generator failures. l l

Sincerely yours, I

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! F. A. Spangenberg(7c 111 Hanager, Licensing and Safety TSA/alb ,

cc: NRC Clinton Licensing Project Manager NRC Resident Office NRC Region III, Regional Administrator Illinois Department of Nuclear Safety

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