ML18052B341

LER 87-031-00:on 870903,diesel Generator Declared Inoperable.Caused by Slow Voltage Regulator Response. Adjustments Made to Diesel Generator Ref Voltage & Voltage Stability Feedback circuit.W/871005 Ltr

ML18052B341
Person / Time
Site:	Palisades
Issue date:	10/05/1987
From:	Johnson B, Kozup C CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
LER-87-031, LER-87-31, NUDOCS 8710090253
Download: ML18052B341 (4)

Text

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~I 20.GC.l 111 lwl I0.7311112111111 I0.71C.11211*l LICENIEE CONTACT FOlll THll LEll 1121 NAME TELEPHONE NUMIER AllEA CODE CSKozup, Technical Engineer, .Palisades COMPLETE ONE LINE FOii EACH COMPONENT FAILUllE DEIClllHD IN THll llll'OllT 1111 MANUFAC-CAUSE SYSTEM COMl'ONENT TUllER B I I Vt R BI 0 I 9 13 Yes I I I I I I I I I I I I I I I I I I I I I IU .EM !N AL llUOllT IXPECTl!D 11'1 MONTH DAY Y~AR EXPECTED n YES (If,,_, - - llXl"llCTED SU*MISSION DATEI SUIMISSION DATE 11111 I I I On September 3, 1987 at 1100, 1-1 diesel generator (DG) [EK;DG] was declared administratively inoperable due to potential deficiencies in the exciter voltage regulator [EK;EXC] response time and the terminal voltage setting. This potential deficiency was identified by Consumers Power engineering personnel through Technical Specification (TS) surveillance procedure data reviews and subsequent computer simulations to model a~cident conditions. The reactor was critical with the Plant operating at 92 percent of rated power when the condition was identified.

While developing and updating the Continuous System Modeling Program (CSMP) for the DG computer model which simulates DG performance using data obtained from TS surveillance procedure R0-8, "Engineered Safeguards Systems", engineering personnel identified that 1-1 DG may not be able to sufficiently maintain output voltage to the required equipment for short periods of time under design basis accident (DBA) conditions. The voltage transient due to starting auxiliary feedwater.

pump [SJ;P] P8A with the "as found" slow voltage time response combined with a low reference voltage setting, created the potential for a loss of the 1-1 DG due to low output voltage. Adjustments were made to the 1-1 DG reference voltage and voltage stability feedback circuit to correct the deficiencies on September 4, 1987. The 1-1 DG was declared operable at 1350 on September 5, 1987 ..

8710090253 871005 NllCF_ . . PDR ADOCK 05000255 Cll-431 S PDR LER 87-031B-NL02

NRC Form lMA U.S. NUCLEAR REGULATORY COMMISSION (9-831 LICENSEE EVENT REPORT (LERI TEXT CONTINUATION APPROVED OMB NO. 3150---0104 EXPIRES: 8/31 /85 FACILITY NAME 11) DOCKET NUMBER 12) LER NUMBER 161 PAGE (3)

Palisades Nuclear Plant 0 15 I 0 I 0 I 0 I 2 I 5 I 5 8 I 1 - 0 I 3I1 - 0 I0 0 I2 OF 0 13

. Description On September 3, 1987 at llOO, 1-1 diesel generator (DG) [EK;DG] was declared administratively inoperable due to potential deficiencies in the exciter voltage regulator [EK;EXC]. These potential deficiencies could have allowed the voltage of 1-1 DG to momentarily drop low enough to trip the DG output breaker or cause a loss of individual loads from the DG. This condition would only occur during the DBA load sequencing of the DG when the last load started, the auxiliary feedwater pump P-8A

[SJ;P]. The rector was critical with the Plant operating at 92 percent of rated power when the condition was identified. The 1-1 DG voltage regulator respoµse time was tested and adjusted on September 4, 1987.

The 1-1 DG was declared operable at 1350 on September 5, 1987.

This potential deficiency was identified by Consumers Power engineering personnel during the development of a computer simulation model of the bus loadings during accident conditions. Data from the February 1986 Technical Specification (TS) Surveillance Procedure (R0-8) was put in:to the computer simulation model. The computer model predicted that under the worst case starting voltage and the observed (as found) voltage response time of the R0-8 data, a voltage collapse would occur when auxiliary feedwater (AFW) pump was started on the loaded bus. The AFW pump P-8A, is 450 HP load and is the last large 2300 V load to be sequenced onto the bus. It is started after approximately 50 seconds by the DBA sequencer.

The auxiliary feedwater pump load was added in 1982 as a TMI follow-up item. The engineering analysis that authorized this addition used a computer model fashioned after a Detroit Edison model and. test data collected from Diesel Generator 1-2. In 1985 Engineering personnel became aware of an improved model developed by Duke Power. As part of the validation effort for the new CSMP model, another set of test data was collected while running surveillance test R0-8, only this time the data was taken on Diesel Generator 1-1. In early September 1987, the computer model was considered tuned and was found to predict the voltage collapse for the 1-1 DG.

Cause Of The Event Our evaluation concluded that under certain conditions the 1-1 diesel generator model predicted a voltage collapse during the start of the auxiliary feedwater pump (P-8A). A voltage collapse resulted from:

1. An improper setting in the feedback circuitry of the voltage regulator assembly.

2. An inadequate reference voltage setting due to the generator shutdown practices.

NRC FORM 366A 19-831 -

LER 87-031B-NL02

NRC Form 3HA U.S. NUCLEAR REGULATORY COMMISSION (9-831 LICENSEE EVENT REPORT (LERI TEXT CONTINUATION APPROVED OMB NO. 3150-0104 EXPIRESo 8/31 /85 FACILITY NAME (11 DOCKET NUMBER (21 LER NUMBER (61 PAGE 131 Palisades Nuclear Plant 0 I5 I 0 I 0 I 0 I 21 5 15 s 17 - 0 I 3 11 - 0 I0 0 13 OF 0 I3 TEXT (If tnOtW _ , , . i6 ,..quirwi, u* -lrionW NRC Form 3116A'al 1171 The root cause of these deficiencies was ini!tlequate knowledge of the importance of these parameters on the response of the DG during the DBA condition. Only after the development of the (CSMP) DG model and the application of the CSMP model to accident conditions were the importance of these parameters and deficiencies discovered. A review of all vendor recommendations and instruction manuals did not uncover any specification or limits on these parameters.

Corrective Actions Upon discovery of the deficiency, the 1-1 diesel generator was declared inoperable at 1100 on September 3, 1987. Sensitivity studies were run to determine the acceptable time response for the voltage regulator*.

Then on September 4, 1987 DG 1-1 was tested and adjusted to obtain the proper voltage response time. In addition, the reference voltage was adjusted to 2400 volts. The diesel generator was declared operable on September 5, 1987.

The monthly DG Technical Specification Test will be revised to ensure the terminal voltage is proper after the completion of the test. In addition, an evaluation of the voltage regulator periodic maintenance and testing will be conducted to assure similar conditions do not reoccur.

Analysis Of The Event The DBA with the loss of one DG is an analyzed transient with rio adverse safety consequences. The CSMP DG model predicts a voltage collapse during a DBA with all of the containment spray pumps and the containment cooling water pumps starting and running. This voltage collapse would prevent the DG from carrying its rated load for a period of time after the AFW pump loaded onto the qus. During the voltage collapse, various loads on the bus would be tripped until voltage recovered. Some of these loads would restart after voltage recovered and others would have to be manually restarted. A prediction of which loads would be lost is beyond the capability of the computer model.

Because the computer model predicts the DG would not have been able to carry its full rated load during a DBA, the DG was declared inoperable.

A review of the maintenance history of the voltage regulator found no record of adjustments to the time response of the voltage regulator during the lifetime of the Plant.

Because the Technical Specifications limit the inoperability of a DG to seven days per month, this event is being reported per 10CFR50.73 (a)(2)(i)(B) as a condition prohibited by the Technical Specifications.

NRC FORM 366A (9-831 LER 87-031B-NL02

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consumers Power POWERINli NllCHlliAN'S PROliRESS General Offices: 1945 West Parnall R~ad, Jackson, Ml 49201 * (517) 788-0550 September 5, 1987 Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 DOCKET 50-255 - LICENSE DPR PALISADES PLANT -

LICENSEE EVENT REPORT 87-031 - DIESEL GENERATOR INOPERABILITY DUE TO SLOW VOLTAGE REGULATOR RESPONSE Licensee Event Report (LER)87-031, (Diesel Generator Inoperability Due to Slow Voltage Regulator Response) is attached. This event is reportable to the NRC per 10CFR50.73(a)(2)(i) and 10CFR50.73(a)(2)(vii).

Brian D Johnson Staff Licensing Engineer CC

• Administrator, Reg_ion III, USNRC NRC Resident Inspector - Palisades Attachment OC1087-0182-NL02