ML17325B228
| ML17325B228 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 06/13/1989 |
| From: | Virgilio M Office of Nuclear Reactor Regulation |
| To: | Greenman E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| References | |
| NUDOCS 8906140294 | |
| Download: ML17325B228 (4) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 June 13, 1989 Docket No. 50-315 MEMORANDUM FOR:
I'ROM:
SUBJECT:
Edward G. Greenman, Director Division of Reactor Projects Region III Martin J. Virgilio Acting Assistant Director for Regions III and V
Division of Reactor Projects III, IV, V and Special Projects Office of Nuclear Reactor Regulation
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DONALD C.
COOK UNIT NO.
1 "CD" DIESEL GENERATOR The Unit I "CD" diesel generator overspeed event on April 10, 1989 prompted an NRR inspection on May 3
& 4, 1989 of maintenance and engineering analysis of the diesel engine and associated equipment.
The inspection team noted that maintenance personnel had evaluated damage to bearing surfaces, cylinders, pistons, connecting rods, pins, engine support structures, and the generator rotor.
Evaluation was performed by boroscopic, visual and dye penetrant exams.
Babbitt surfaces demonstrated near failure conditions resulting in replacement of most main crankshaft bearings.
Examinations of cylinders, pistons and connecting rods revealed no damage.
As a result of excess vibration the engine pedestal shifted slightly.
The generator rotor was replaced as a precautionary measure and the diesel generator combination was rea 1 igned.
The I C department discovered a
lack of continuity between the speed pickup and the electronic trip circuitry.
A bad solder connection on a cannon plug was determined to be the cause of the tailure of the overspeed trip.
The evaluations of hardware problems provided by the licensee's maintenance personnel were determined by the NRC inspectors to be adequate and the repairs that were performed appeared to be satisfactory.
'Ihe inspection team also reviewed and discussed the licensee's engineering analysis as to the cause of the overspeed event.
DC Cook personnel attributed the event to a combination of several factors.
These factors included the fuel rack governor control arm position and individual injector adjustments which resulted in fuel being delivered to the engine in quantities greater than what the governor could compensate for under no load conditions.
The excess fuel was the result of minor adjustments made to increase fuel to 4-6 cylinders for the purpose of achieving engine exhaust temperature balance.
The individual injector adjustments were made during a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> run of the diesel engine to equalize temperature for crankshaft deflection measurements.
CONTACT:
A. T. Gody, Jr.
492-1305 8906i40294 8906i3 PDR ADOCK 050003i5 PDC
Edward G. Greenman June 13, 1989 In response to these discussions and concerns raised by the inspection
- team, on May 11, 1989, the licensee conducted a test to substantiate their root cause analysis.
In this test, the Unit 1 "CD" diesel was stabilized at a speed of 440 rpm (no load),
and the number 6
FB cylinder fuel was increased by approximately 1/4 turn inward of the fue1 pump control shaft lever screw.
Engine speed was observed to increase slowly and at a constant rate to 520 rpm when operators took manual control to prevent an overspeed condition and the test was terminated.
Based on this single data point, the licensee concluded that the original root cause analysis was adequately substantiated and no further testing or analysis was required.
The NRR staff is concerned about the validity of the licensee's assumptions regarding the root cause of the overspeed event and questions whether this single test adequately demonstrates AEP's hypothesis.
In evaluating the licensee's root cause analysis, Mr.
Ed Tomlinson made the following observations that tend to discount their conclusions.
The functional horsepower curve for diesel
- engines, regardless oi load, increases as a square function with engine speed.
Frictional horsepower represents losses within the engine, and the fuel flow to the engine must also increase exponentially in order to offset these losses if a continual increase in engine speed is to be substantiated.
Fuel increase, however, to an engine for a given fuel control setting (rack setting) is linear with engine speed.
Therefore, the fuel plot and functional horsepower curve must intersect at some equilibrium point.
Performing a rough curve fit using data given to the NRC by the licensee concerning rack setting and engine loading and intersecting the linear fuel plot, the equilibrium point has to be a speed value that represents a smaller percentage speed increase than the percentage fuel increase.
The above discussion is based on a fixed rack setting for the whole engine.
Fuel to individual cylinders can be increased relative to this fixed setting, but the base rack setting does not change.
For the test described
- above, the licensee stated that the rack setting did not change.
Nevertheless, the test results show that less than a
1% increase in fuel (adjusted at the no.
6 FB injector) resulted in no less than a 20K increase in speed with the possibility of an even greater speed increase.
This would indicate that factors other than those identified by the licensee should be considered in determining the cause for the overspeed condition.
At
- best, we feel that these tests should be considered inconclusive.
Additionally, the licensee has not shown adequate concern over the validity of the root cause analysis.
Further investigation is recommended to ensure no similar events occur in the future.
Additionally, due to the potential generic implications, it is important that we and the licensee understand what actions or inactions led to the damage of this safety-related piece of equipment.
We understand the licensee has repaired, tested and declared the Unit No.
1 "CD" diesel generator operable.
We feel that the Region is in the best position to
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Edward G. Greenman June 13, 1989 address the adequacy of the operability determination andreliability of the diesel generators.
Accordingly, we request you assume the lead in closing out this issue.
Please contact us if we can provide further technical analysis.
,I Original Sfgnedby:
I Martin J., Virgilio
'cting Assistant Director for Regions III and V
Division of Reactor Projects,'III, IV, V and Special Projects DISTRIBUTION II<<ET I 'I= 1'5)
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