ML20238D645

Special Rept:On 870804,diesel Generator 2B Experienced Valid Failure & Two Invalid Failures.Caused by Slow Starts Due to Unknown Reasons.Operability Test Changed to Require Governor Oil Level to Be Verified as Correct on Prestart Checklist

ML20238D645
Person / Time
Site:	Mcguire
Issue date:	09/03/1987
From:	Tucker H CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
NUDOCS 8709110302
Download: ML20238D645 (6)

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DUKE POWEn GOMPANY P.O. DOX 33180 CIIAHLOTTE, N.C. 28242

, * ,f (7437 4 1 l September 3, 1987 U.S. Nuclear Regulatory Commission l

.' Document - Control" Desk" '

Washington, D.C. 20555

Subject:

McGuire Nuclear Station Decket No. 50-370 Technical Specification 4.8.1.1.3 and 6.9.2 Gentlemen:

Please find attached a special report submitted pursuant to Technical Speci-fication (T.S.) 6.9.2 as specified by T.S. 4.8.1.1.3. The report concerns Diesel Generator 2B experiencing a valid failure and two invalid failures due to slow starts.

This event is considered to be of no significance with respect to the health and safety of the public.

Very truly yours,

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4 Hal B. Tucker SEL/108/jge Attachment xc: Dr. J. Nelson Grace INPO Records Center Regional Administrator, Region II 1820 Water Place U.S. Nuclear Regulatory Commission Atlanta, Ga 30339 101 Marietta St., NW, Suite 2900 Atlanta, GA 30323 Mr. Darl Hood Mr. W.T. Orders U.S. Nuclear Regulatory Commission NRC Resident Inspector Office of Nuclear Reactor Regulation McGuire Nuclear Station Washington, D.C. 20555

/ o 9709110302 870903 i I

PDR ADOCK 05000370 s PDR

Diesel Generator Special Report Diesel Generator 2B Experienced A Valid Failure .

And Two Invalid Failures Due To Slow Starts Caused By Unknown Reasons '

i INTRODUCTION:

On August 4, 1987 at 0945, Diesel Generator 2B exceeded the eleven second maximum allowable start time to achieve 4160 VAC required by Technical Specification 3/4.8.1 during a routine start for operability verification. During troubleshooting of this Valid Failure, Diesel Generator 2B also experienced two '

Invalid Test Failures due to slow start times. The cause for the. slow starts could not be determined by Instrumentation and Electrical or Mechanical Maintenance. One acceptable start time was experienced between the two Invalid Test Failures.

Three subsequent Diesel Generator 2B starts were within acceptable time limits.

Operations completed the routine operability test successfully during the third consecutive acceptable start and declared Diesel Generator 2B operable at 1910 on August 4, 1987.

1 Unit 2 was in Mode 1, Power Operations, at 100% power during the time of this incident.

This incident has been assigned a Cause Code of Other, since the root cause of the slow starts is unknown.

f EVALUATION:

Bachround Each unit at McGuire Nuclear Station has two independent diesel generators (D/Gs).

These D/Gs are used to provide standby alternating current (AC) power to the equipment required to safely shutdown the reactor in the event of a loss of normal power. The D/Gs also supply power to the safeguard equipment as required during a major accident coincident with a loss of normal power (blackout).

Technical Specification (TS) 3/4.8.1 requires both independent D/Gs to be operable in Modes 1, 2, 3, and 4. One of the routine surveillance requirements of TS 3/4.8.1 is to verify that the D/Gs start from ambient conditions and accelerate to 4160 VAC in i 11 seconds. With one D/G inoperable, the action statement requires that all required systems, subsystems, trains components, and devices that depend on the remaining operable D/G as a source of emergency power are also operable.

The action statement also requires that 2 offsite power sources are verified to be operable within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and each 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> thereafter, the Steam Driven Auxiliary Feedwater Pump is demonstrated to be operable, and that the remaining D/G is demonstrated to be operable within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Table 4.8-1 of the TS specifies the '

test frequency required for D/Gs according to the number of failures in the last 20 and last 100 valid tests. If the number of failures in the last 20 valid tests is greater than or equal to 2 or the number of failures in the last 100 valid tests is greater than or equal to 5, the required test frequency increases from once each 31 days to once each 7 days.

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Each diesel engine is controlled by a Woodward EG-B35 Governor / Actuator. There 'i are two separate sections to the Governor; the mechanical Governor section is a

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standard fly-weight type. speed sensor which modulates te hydraulic pilot valve, and the electrical Governor: ...section is an electrically operated pilot valve which responds to signals from en electronics package which measures engine speed and power. The pilot valves .in each section operate small hydraulic cylinders, which are each connected tcJ opposite ends of a lever. The middle of the lever is connected to another pilot valve, which modulates an output hydraulic cylinder.

This last hydraulic cylinder acts as a hydraulic amplifier and is connected to the fuel rack (throttle). This arrangement allows either or both of the governing sections to centrol the output to the fuel rack.

F.ach of the two sections of the Governor has its own independent speed setpoint, and the electrical section is adjusted and eet by means of a procedure. The nominal setpoint for the mechanical section is equivalent to 63 Hz, and the setpoint for the electrical section is equivalent to 59.5 Hz (60 Hz is equivalent to 514 RPM). During stea'y d state operation, the electrical section dominates and controls the engine power output with the mechanical section functioning as a backup. During an engine startup, a Servo-booster uses starting air to initially control the output to the fuel rack. At approximately 50% of rated speed, the {

l mechanical Governor assumes and essentially maintains control until approximately f 95% of rated speed. The electrical Governor may begin to assist as the diesel i approaches full speed. The fuel rack is normally maintained fully opened by the Servo-btoster and Governor during a D/G startup until full speed is attained.

s Descr y on of Incident on August 4, 1987, Operations attempted to ra "T/2/A/4350/02B, Diesel Generator "2B" Operability Test. At approximately 0940, D/G 2B was started and took 11.5 seconds to reach 4160 VAC (start No. 564, Valid Failure) . Th'e time between 95%

speed and 4160 VAC was approximately normal (1.9 seconds), but the time to reach 95% r, peed was slower than normal by approximately 1 second.

Operatious wrote a work request to have the problem investigated, and Instrwnentation and Electrical (IAE) arrived in the early afternoon to troub2eshoot for the cause of the slow start. Operations started D/G 2B at 1308 with IAE present. The D/G reached 4160 VAC in 11.3 seconds dter the start, again reaching 95% speed appro.rinately 1 second later than normal. Operations started <

D/G 2B again at 1333, and on this occasion, the D/G reached 4160 VAC within 11 j seconds. No electrical abnormalities vere observed by IAE on either of these two starts.  !

I IAE.and Operations did note that the oil sight ginss level in the Governor';;uk or remained the same af ter the D/G was started, whereas Governor oil level usually decreases slightly when a D/G is started. Also, a small amount of oil was visible eround the outside of the sight glass. i

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9t 1531, Operations again started D/G 2B. This time D/G 2B reached 4160 VAC in J6,2 seconds and the diesel was audibly dragging. IAE observed the fuel rack oscillating during the time when it was supposed to remain fully open. Again the tim from 95% speed to 4160 VAC was approximately 2 seconds as expected. A " Low Crankcase Vacuum" alarm sounded and cleared a couple of seconds af ter D/G 2B was started.

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Operations then called Mechanical Maintenance (MNT) to aid in troubleshooting.

MNT observed the next three starts of D/G 2B. In all of the three starts, D/G 2B achieved 4160 VAC within 11 seconds, and MNT noted no abnormalities other than the Governor oil level increase.. MNT verified that the starting air pressure was normal and that the fuel rack was fully open during all the starts.

MNT and IAE called a Woodward Governor Company representative to discuss the possibility that ' the Governor might be' causing the slow starts. The Woodward representative did not believe the Governor was causing the problem but suggested that MNT check the vent port at the top of the Governor oil sight glass to ensure that it was not plugged. (MNT subsequently checked the port and found it open.)

On the third consecutive acceptable start, Operations completed the D/G 2B operability test successfully (start No. 570, Valid Success) and declared D/G 2B operable at 1910.

Conclusion This incident consisted of one Valid Failure and two Invalid Failures of D/G 2B.

The Valid Failure was the 6th failure in the last 100 valid attempts for D/G 2B and the 3rd failure in the last 20 valid attempts. The test frequency required by the TS for these ratios is once every 7 days , the same frequency which was required prior to this failure.

This incident has been assigned a Cause Code of Other, since the root cause of the slow starts of D/G 2B is unknown. D/G 2B has started in an acceptable amount of time in 2 starts classified as Inyslid Tests for troubleshooting and 3 starts classified as Valid Successes, since the last slow start.

-Operations is required to verify the Governor oil sight glass is full on D/G startup checklists and check that the oil level is midway on the sight glass while the D/G engine is idling. One abnormality noted during the troubleshooting of the problem with D/G 2B was that the oil level in the Governor sight glass did not decrease from full to midway when D/G 2B was started. Operations routinely see the Governor oil level decrease during starts of the other 3 D/Gs. However, the Governor on D/G 2B is a new Governor installed on May 6, 1987. The Woodward representative consulted stated that an increase in oil level in the sight glass during a start may be " normal" for this Governor. This theory is supported by the fact that the oil level has not decreased during any of the acceptable starts on August 4,1987 and af ter.

Two anomalies were noted by Operations which happened only during the 16.2 second start during troubleshooting on August 4. A " Low Crankcase Vacuum" alarm actuated a couple of seconds into this start, and the fuel rack oscillated when it should have been fully open. The reasons for these abnormalities could not be determined during troubleshooting or this investigation.

MNT conducted extensive preventive maintenance on D/G 2B from June 1, 1987 to June 16, 1987. The oil in the Governor was changed on June 13, 1987 as part of the routine maintenance. D/G 2B experienced a valid Failure due to a slow start on June 21, 1987 after the D/G post maintenance break-in runs were completed.

Although the cause of this slow start could not be determined, air in the Governor

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, ur oil lines was cited as a possible cause for this slow ~ trt. ID was, further stated that there are no provisions to bleed air from the s <.rnor oil lines after oil is added and that the DOsel would have to be operated to purge, c # any air in ,I the Govcrnor oil lines. Woodward rep 'esentatives consulted concming the June a 21, 1987 slow start said that air in the Governor oil lines r.f nt h cause slow starts, but not necessarily on the first run af ter the oil was added. Woodward representatives consulted during this investigation did not believe thab the slow starts on August 4, ,

1987 could be attributed to air in the oil lines) since 10  !

consecutive acceptable ster;ts had occurred since the oil change out. l-A review of past McGuire Reports revealed 4 other reports documenting slow starts 1 of D/Gs. A slow start of D/G 2B occurred due te a failed capacitor on the Exciter Voltage Regulator circuit card. However, the symptoms were different from the i August 4, 1987 slow starts. The time to 95% speed was normal and the time.Letween I 95% speed and 4160 VAC was longer than normal when the Fxciter Voltage Regulator malfunction occurred. /g

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- An Invalid Failure of D/G 2A ejcurred due to a slow start during a post ,

maintenance break-in run. No correctWe actions were planned since a ' slow stagt is not unexpected during a break-in run. , Another slow start of D/G 2B occurred. q for unknown reasons. No corrective Etions were planned since the . failure mpe could not be determined and subsequent'aiarts were successful. <

.Since there have been two previous slow starts of a D/G with no clear indication of a cause, this incident is considered to be recurring.

This incident is not reportable to the Nuclear Plant Reliabil ty Data System f (NPRDS).

'1 CORRECTIVE ACTIONS:

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Immediate: None

, i Subsequent: 1) The D/G 2B Operability Test was changed to require the Govarnor oil level to be verified as correct on the pre-startup checklist. '

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2) General Offict Nuclear maintenance observed the next routine start of D/G 2B and datermined that no further corrective t actions are needed.

Planned: None

' SAFETY ANALYSIS:

During the time that D/G 2B was inoperable, Operations performed the surveillance necessary to verify the offsite f.C power sources were ave.11able, the steam driven auxiliary feedwater pump was opierable, and that all requirtd systems, subsystems, , i trains, components, and devices that depend on f he remsging D/G as a source of emergency power were opersH4. D/G 2A was demonstrut.W operable within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of D/G 2B being declared di operable as required by tue TS. Therefore, there was sufficient power . available to supply the safet)-related kquipment required for:

(1) the safe shutdown of t.'y facility, and (2) , the mitigation and control of accident conditions within the, facility. f

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' There were l-- no fpersonnel . " injuries, personnel, overexposure, or releases 'of

- radioactive material as a result of this. incident.

", This. incident is considered'to#- be of' no significance with respect to ' the Walth and safety of the public, s r2 7> :2

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