ML20154P516

Special Rept:On 880419,25 & 0505,diesel Generator Valid Failures Occurred Due to Pressure Sensor Design Flaws.New P3 Pressure Sensor Inspected,Calibr & Installed & Generator Declared Operable After Operability Test

ML20154P516
Person / Time
Site:	Catawba
Issue date:	05/25/1988
From:	Tucker H DUKE POWER CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
NUDOCS 8806030361
Download: ML20154P516 (25)

Text

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DUKE POWER GOMIRNY P.O. DOX 03180 CHARLOTTE, N.C. 28242 HAL H. TUCKER TELEPlf 0NE '

nca parassent (704) 073-4501 stuna Pacoterior May 25, 1988 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D. C.

20555

Subject:

Catawba Nuclear Station, Unit 1 Docket No. 50-413 Special Report Gentlemen:

Pursuant to Technical Specification 3/4.8.1.1.3, please find attached a Special Report concerning the Diesel Generator (D/G) 1A 7th, 8th and 9th valid failures in the last 100 Unit i valid tests which took place on April 19, 1988, April 25, 1988 and May 5, 1988. This report has been expanded to include aupplemental information required by Regulatory Guide 1.108 as it was indicated in my May 19, 1988 letter regarding the 7th valid failure in the last 100 D/G 1A valid tests.

Very truly yours, W

Hal B. Tucker JGT/27/sbn i

Attachment xc:

Dr. J. Nelson Grace, Regional Administrator U. S. Nuclear Regulatory Commission Region II j

101 Marietta Street, F., Suite 2900 1

Atlanta, Georgia 30323 Mr. P. K. Van Doorn NRC Resident Inspector Catawba Nuclear Station i

1 n

8806030361 880525 PDR ADOCK 05000413 i

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MAY 25, 1988 DUKE POWER COMPANY CATAWBA NUCLEAR STATION, UNIT 1 SPECIAL REPORT REGARDING DIESEL GENERATOR 1A VALID FAILURES ON-APRIL'19, 1988, APRIL 25, 1988 AND MAY 5, 1988 DUE TO PRESSURE SENSOR DESIGN FLAWS l

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[IIR C88-54-1)

[IIR C88-55-1)

[IIR C88-60-1) l qp'l

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ATTACRMENT 1 DUKE POWER COMPANY-CATAWBA NUCLEAR STATION t

DIESEL GENERATOR 1A VALID FAILURES DUE TO PRESSURE SENSOR DESI,GN FLAWS INTRODUCTION:

While performing the operability verification test on Diesel Generator (D/G) 1A (Start Attempt #662) on April 19, 1988, at 0815 hours0.00943 days <br />0.226 hours <br />0.00135 weeks <br />3.101075e-4 months <br />, the D/G tripped after approximately 60 seconds, D/G 1A was declared inoperable and Work Request (W/R) 27635 OPF was written to investigate / repair the cause of the trip.

D/G 1A was started two more times with IAE personnel present but no failure occurred. Additional troubleshooting did not.

reveal the cause of the trip, therefore, all sens'brs that could have contributed to the trip and the pneumatic logic board were replaced.

Start attempt #662 was declared a valid failure. This was the 5th valid failure in the last 20 valid starts on D/G 1A and the 6th in the last 100 valid starts. The surveillance interval was at least once per 7 days following the valid failure, which is in accordance with Technical Specifications Surveillance 4.8.1.1.2.

This is the seventh valid failure in the last 100 valid starts on Unit 1 D/Gs.

On April 25, 1988, at 1035 hours0.012 days <br />0.288 hours <br />0.00171 weeks <br />3.938175e-4 months <br />, during its operability test, once again Diesel Generator (D/G) 1A tripped after approximately 60 seconds.

D/G 1A was declared inoperable and Work Request (W/R) 27606 OPS was initiated to investigata the cain e of the failure.

D/G 1A was started several more times for I AE's tr.ableshooting purposes and again shutdown af ter approximately 60 seconds.

It was discovered that the P3 pressure sensor in Diesel Engine Control Panel 1A (IDECPA) was not resetting causing it to vent continuously and subsequently shutdown the engine.

Start attempt number 676 was declared a valid failure. This was the eighth valid failure in the last 100 valid starts on Unit 1 D/Gs. A new P3 sensor was inspected, calibrated, and installed and D/G 1A was declared operable after its operability test on April 27, 1988.

On May 5, 1988, at 1105 hours0.0128 days <br />0.307 hours <br />0.00183 weeks <br />4.204525e-4 months <br />, D/G 1A was started for its operability test.

Again, the engine shutdown after approximately 60 seconds.

During the time period between this failure and when-D/G 1A was declared operable on April 27, 1988, the engine was successfully run on two occasions.

IAE's troubleshooting revealed that the P3 pressure sensor was again not resetting and venting continuously on an engine start.

Start attempt number 691 was declared a valid failure. This was the ninth valid failure in the last 100 valid starts on Unit 1 D/Gs.

A representative from Calcon Incorporated, the sensor's manuf acturer, arrived on site to assist with our problems.

It was determined that manufacturing and design flaws in the sensor prevented it from resetting.

A new P3 sensor, inspected by the manufacturer's representative, was installed and D/G 1A was declared operable following its operability test on May 8, 1988.

Per Technical Specification (T.S.) 4.8.1.1.3 and Regulatory Guide 1.108, a special evaluation of the Diesel Generators reliability is required when the number of valid failures is seven or greater in the last 100 valid starts on a per unit basis. Attachment 2 addresses this requi sment. This report combines the seventh, eighth, and ninth valid fail?

s due to the root cause being the same.

_. =

o Paga 2 of 7' Unit 1 was in Mode 1, Power Operations, at 100?. power at the time of all three valid failures. D/G 1A was unavailable for approximately 58 hours6.712963e-4 days <br />0.0161 hours <br />9.589947e-5 weeks <br />2.2069e-5 months <br /> following the 7th valid failure, 51 hours5.902778e-4 days <br />0.0142 hours <br />8.43254e-5 weeks <br />1.94055e-5 months <br /> following the 8th valld failure,.

and 69 hours7.986111e-4 days <br />0.0192 hours <br />1.140873e-4 weeks <br />2.62545e-5 months <br /> following the 9th valid failure.

EVALUATION:

Background

Each unit at Catawba Nuclear Station has two independent diesel generators manufactured by IMO Delaval, Incorporated. These D/Gs are used to provide an emergency standby source 6f power to tba equipment required to safely shutdown the reactor in the event of a loss of normal power. The D/Gs also supply power to the safeguards equipment as required during a major accident coincident with a loss of normal power (blackout).

Each D/G is controlled by a separate 60 psi pneumatic control system that will trip the engine when the setpoints of various parameters are reached. This process is achieved by the venting of sensors causing the pneumatic

• shutdown logic board to initiate a shutdown signal. Trips ara divided into Group I and Group II trips.

Group II trips are locked out for a period of 60-90 seconds from engine start te allow time for certain engine parameters to reach their normal operating state. On an emergency start, all trips are blocked except lo lo lube oil, overspeed, and generator differential.

Lo Lo lube oil trip is a Group II trip.

It is blocked, even on an emergency start, for 60-90 seconds, then it is activated. This blocking is obtained by use of the P3 pressure sensor which is in line with the lo-lo lube oil sensors. (See Enclosure 1.)

On an engine start, P3 is pressurized and blocked via port 9 of the logic board.

Thi_ allows time for the lo lo lube oil sensors to block and its tubing line to pressurize. This pressure should hold P3 pressurized when port 9 pressure is lost after the 60-90 second lockout period is terminated.

If process pressure to P3 is not obtained or is lost, P3 will vent and the engine will trip when the lockout period is over.

l All the sensors on the engine and P3 in the control panel are manufactured by California Controls Company, Inc. (Calcon). A total of seven of these sensors are of one particular model #: Calcon B4400 l

(Delaval part # F-573-156).

These sensors are used in the following locations:

3 lo lo lube oil trips, lo lube oil trip, 2 turbo lube oil trips, and P3 pressure sensor.

Description of Event On April 19, 1988, at 0815 hours0.00943 days <br />0.226 hours <br />0.00135 weeks <br />3.101075e-4 months <br />, D/G 1A was started (start attempt #662) to perform an operability test.

The engine ran approximately 60 seconds

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and tripped with all Group II trip annunciators displayed.

D/G 1A was declared inoperable and W/R 27635 OPS was written to investigate and repair the cause for the trip.

IAE personnel had Operations start the engine again, but this time, no trip occurred.

Several more starts were performed but no trips occurred.

IAE removed the following Group II

9 Pags 3 of 7 instruments:

Lo lube oil trip sensor, left and right front turbo oil trip sensors, Hi crankcase pressure trip sensor, and the pneumatic logic board. Each of these were checked on the bench and no abnormalities were seen. Nevertheless, each of these were replaced due to concerns that an intermittent problem could possibly_ exist with one of them.

In addition, calibration was verified on the Hi Temperature Jacket water sensor and the three Lo-Lo Lube Oil sensors, which had been replaced on April 12, 1988. No problems were found that could have caused the trip.

The next day, D/G 1A was started again.. IAE monitored test gauges installed in the pneumatic lines to aid in troubleshooting should a trip occur again. The D/G did not trip, but the trip lines did not pressurize-fully until just seconds before Group II swap-over occurred. The D/G was started several more times and all pressures looked normal.

D/G 1A was secured and IAE continued to troubleshoot. All instrument-tubing lines that could have caused a trip were pressurized and verified not to leak.

During this process, it was discovered that the.004 orifice check valve, Item #31 on Enclosure 1, was leaking past its seat. The.004 orifice.

check valve was removed along with the P3 pressure sensor.

It was IAE's feeling that tha.004 orifice check valve leaking was not significant enough to cause the D/G failure that had occurred.

The orifice check valve was replaced and P3 was checked to verify proper calibration.

The P3 tested good and an inspection revealed no problems with it.

Nonetheless, it was replaced. D/G 1A was run three times and no problems were seen.

D/G 1A was allowed to sit idle for a period of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to try and establish a correlation between time and the failures. The previous valid failure on D/G 1A on April 12, 1988 could also not be repeated after the engine had been started in a short time period fc b.aing the trip.

D/G 1A was started and all pressures increased and stabilized as they should. The engine was run twice more and everything looked normal. The operability test was then run and D/G 1A was declared operable.

Temporary Station Modification (TSM) W/R 9238 IAE, which allowed installation of pressure gauges on the Group II pneumatic trip lines, was installed in IDECPA on April 22, 1988.

This modification would allow IAE to inonitor these pressures during the operability tests.

This was a useful tool to help pinpoint any problem areas that could possibly trip the D/G but were not reproducible on the.next run.

D/G 1A was started on April 23, 1988 and all indications were normal.

On April 25, 1988, at 1035 hours0.012 days <br />0.288 hours <br />0.00171 weeks <br />3.938175e-4 months <br />, D/G 1A was started (start attempt number 676) to perform an operability test.

The engine ran approximately 60 seconds and tripped with all the Group II trip annunciators displayed. D/G 1A was declared inoperable and W/R 27606 OPS was initiated for IAE to investigate the reason for the trip.

IAE technicians monitoring the gauges installed per TSM 9238 IAE on the trip lines noticed that none of these lines built pressure during the start attempt. Operations started the engine several more times for IAE's troubleshooting purposes. Each time the engine tripped after approximately 60 seconds.

It was discovered that the P3 pressure sensor was venting continuously during the engine run which was causing D/G 1A to trip.

P3 was removed and checked on the tench.

It was determined

q 9

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,s Attachmsnt 1 Pags 4 of 7 that its setpoint had drif ted from its calibrated value of.40 psi to 1

greater than 60 psi. This P3 had just been replaced on April 20, 1988 per Work Request 27635 OPS. D/G 1A had run on 2 different occasions (April 21, 1968 and April 23, 1988) with no problems since this P3 was replaced on April 20.

The failed P3 was disassembled'and inspected.

Slight manufacturing defects'such as inadequate deburring were the only things observed internal to the sensor that could have been attributed to the failure.

The sensor was reassembled and recalibrated to 40 psi decreasing. The sensor was repeatable at this setpoint when cycled several times.

A new sensor was removed from stock, inspected thoroughly, calibrated for 40 psid, checked for repeatability, and installed in IDECPA for use as the P3 pressure sensor.

D/G 1A was allowed to sit idle for a day to ensure that time was not a' factor in the trip. On April 27, 1988, D/G 1A successfully passed the operability test and was declared operable.

Work Requests 9249 IAE, 9250 IAE, and 9251 IAE were written on April 28, to inspect the group II sensors on D/Gs 1B, 2A, 2B, respectively for-manufacturing flaws and corrosion caused by moisture in the Instrument Air (VG) System. The sensors were cleaned /rapaired/ replaced as necessary.

Lo Lo lube oil sensor C on D/G 2B was found to have the same failure mode as the P3 that failed on D/G 1A.

It would vent continuously when 60 psi process pressure was applied.

It was replaced and returned l

to service.

Because of chis being a 2 out of 3 trip, this failure did not show up in the D/G 2B runs.

Meanwhile, D/G.1A was run successfully J

on April 29 and May 3, 1988, and no problems were encountered.

On May 5, 1988, at 1105 hours0.0128 days <br />0.307 hours <br />0.00183 weeks <br />4.204525e-4 months <br />, D/G 1A was started (start attempt #691) for its operability test.

After approximately 60 seconds, once again, the engine tripped with all Group II trip annunciators displayed. D/G 1A

)

was declared inoperable and W/R 27726 OPS was initiated for IAE to l

investigate the cause of the failure.

It was discovered that the P3 that j

had been just changed out on April 25, 1988, had failed.

It would not reset with 60 psi control air pressure applied on it, indicating the same failure as the previous P3.

The P3 pressure sensor was removed from 1DECPA and brought to the IAE shop for troubleshooting.

It was initially thought that the setpoint had drifted greater than 20 psi above the required setpoint of 40 psi. The sensor was adjusted to 40 psid and verified to reset at approximately 48 psi increasing, giving a deadband i

of 8 psi. The sensor was allowed to sit for about 45 minutes. When checked again, on an increase in pressure, it would not reset up to 60 psi. More troubleshooting was performed and it was discovered that if more pressure was applied, the sensor would eventually reset and still retain its setpoint of 40 psi. The longer the sensor sat, the higher the deadband would be.

An IMO Delaval and Calcon representative arrived on site at IAE's request on May 7th, 1988, with 12 new Calcon Model B4400 pressure sensors that had been closely inspected. They observed first hand the problems that were being encountered.

It was determined that a batch of sensors received on April 15, 1988, were of poor quality. The three that had failed (2 P3s and 1 Lo Lo Lube Oil) were of this lot. The Calcon rep l

pointed out that friction binding between the large spring and spring i

a s

.e Attachmtnt 1 Paga 5 of 7 housing internal to the sensor (see Enclosure 3) could lead to the high reset values that were seen. ' Work Requests 9277 IAE, 9278 IAE, and 9279 IAE were written to replace sensors from the suspect batch on D/Gs

'2A, 2B, and 13 respectively.

In addition, W/Rs 9282 IAE, 9283 IAE, and 9281 IAE were written to vecify that the reset pressures for the P3 on D/Gs 2A, 2B, and 1B respectively, were not abnormally high. The P3 in IDECPA was replaced with one delivered by the vendors per W/R 27726 OPS.

The other sensors of this type on D/G 1A were not from the suspect batch, and therefore were not replaced.

Also during this same time period, to ensure complete reliability of D/G 1A, the decision was made to replace the VG supplied control air system, which had been plagued with a moisture problem over the years, with a nitrogen supplied system. This modification was performed per Nuclear Station Modification (NSM) #CN-11151.

This modification was completed and tested on May 8, 1988. Operations completed their operability test the same day and D/G 1A was declared operable.

On May 9, 1988, at approximately 1430 hours0.0166 days <br />0.397 hours <br />0.00236 weeks <br />5.44115e-4 months <br />, a call was received from the IMO Delaval Rep. He stated that the Calcon Rep, after leaving Catawba, made more discoveries about the suspect model of sensors.

It was requested that the IMO Delaval and Calcon Rep visit the site once more with some newly modified sensors and assist IAE with replacing all sensors of this type on each engine.

The IMO Delaval Rep stated that the engines were not inoperable with the sensors that were currently installed, however, the additional measure of replacing the sensors was needed. The Calcon and IMO Delaval Rep. arrived on site on May 11, 1988, with more new sensors.

They explained in detail the discoveries about the sensors that had been determined to be the main reason they had failed.

Because of a tolerance stack-up in the manufacture of the sensor, the pressure sensing diaphragm can be held solid against the pressure head, thus creating a smaller surface area (see Enclosure 3).

This smaller surface area would require a much higher pressure to reset the sensor.

Calcon had remanufactured the pressure head on the new sensors brought with them to add an additional 1 1/8" diameter circular bore.030" deep, to provide a positive gap between the head and the diaphragm. The new sensors will be stamped P/N B4400B to distinguish them from the questionable sensors.

All Calcon B4400 sensors were replaced on D/Gs 1A, 1B, 2A, and 2B per W/Rs 9295 IAE, 9296 IAE, 9297 IAE, and 9298 IAE with Calcon B4400B sensors.

CONCLUSION Based on the discoveries made by Calcon, it is concluded that the 7th, 8th, and 9th valid failures within the last 100 valid starts on Unit 1 D/Gs are attributed to the same root cause:

inadequate design and manufacture of the Calcon Model B4400 pressure sensor.

Upon returning to his plant on May 9, 1988, the Calcon Rep discovered that by stacking up the tolerances allowed in the manufacture of the sensor, it was possible to have negative

.022" or no gap between the diaphragm (P/N 283) and the pressute head (P/N 4370).

(See Enclosure 3.)

If all parts were in the middle of these tolerances, there would be a.010" gap.

And, if the parts were at the other extreme of the tolerances, then a.030" gap would be present.

The ef fect of the negative gap would cause the diaphragm to fuse to the

Attachmtnt 1 Pags 6 of 7 pressure head from spring pressure on the pressure plate (p/n 4380). This in turn reduced the normal pressure area of approximately 1 1/8" diameter down to 3/8" diameter, thus requiring more pressure to overcome the spring pressure and reset the sensor.

On newly calibrated sensors, this is not seen because the diaphragm has not had time to stretch and seat itself against the pressure head. This explains the time factor involved in the failure of these sensors. The failed sensors, including the P3 removed after the 7th valid failure, were measured and verified to have a negative difference between the diaphragm and pressure head, indicating the diaphragm was actually being compressed. This was also evident from inspecting the diaphragm and noting the compression ring on the diaphragm.

Calcon's modification to this type of sensor ensured that a positive gap will always be present between the diaphragm and the pressure head. With all of these type sensors being replaced, no further failures of this type should exist. Further smrification of the effectiveness of this modification wat demonstrated by calibrating 2 of the failed sensors and checking. reset pressure. After a period of time, reset pressure was seen to raise significantly.

The modification of taking.030" from the inside of the pressure head was then performed on these 2 sensors.

They were again recalibrated and allowed to sit overnight. The next day they were checked and reset pressure had not changed.

This design flaw had a significant effect on D/G operation.

All of these sensors are set on a decreasing pressure to trip the engine. However, the reset pressure is critical also.

If the sensor is not reset on an engine start, ther it will vent continuously and not allow pressure to build up in any of the pneumatic lines. This explains why all annunciators for Group II trips were received during these 2 failures. The reason the defect was so pronounced with a sensor used in the P3 application was because the setpoint of 40 psid is higher than the other sensor applications:

lo lo lube oil, 30 psid; lo turbo oil, 15 psid; lo lube oil, 35 psid. This means that a higher spring pressure must be overcome to reset the sensor.

Also, lube oil pressure, which other sensors are seeing, actually increases higher than 60 psi which the maximum P3 would ever sense.

Per Calcon, this design flaw has existed since 1980, as none of the parts involved have had changes affecting these tolerances. From inspections performed by the Calcon Rep on site it was noted that approximately 40%

of the sensors checked actually had a negative clearance between the diaphragm and the pressure head.

It so happened that the ones with this discrepancy were used in the P3 application on D/G 1A during the 7th and 8th, and 9th valid failures.

A problem with air quality in the VG system has been a major concern over the past months, in particular on D/G 1A.

Several older sensors that had been removed following the D/G 1A failures were seen to have a degree of corrosion in their internals. This corrosion was initially thought to be a major contributing factor in the failures on D/G 1A due to it possibly causing sensors to stick in the vented position. Maintenance history showed that the VG system for D/G 1A had been exposed to more moisture carryover problems from the system's aftercoolers over the past several years than the other D/Gs. Inerefore, following the 9th valid failure, it was decided to replace the VG supplied pneumatic control system with a nitrogen supplied system to further ensure the reliability of D/G 1A.

.5

-Attachmsnt 1 Pags 7 of 7 l

j l

The nitrogen system will supply a clean and dry source of control medium. The aftercoolers on all 4 D/G's VG System dryers are now being I

blown down twice a shift to remove moisture buildup. Also, Performance l

is monitoring-the moisture content in all 4 D/G's VG Systems on a more-l frequent basis. Other measures to improve long term reliability are detailed in the special report, Attachment 2.

i SAFETY ANALYSIS:

Technical Specifications requires that when either an offsite AC electrical power source or D/G is inoperable, the availability of the remaining power sources must be demonstrated. This was done each time D/G 1A was inoperable per Tech Spec guidelines.

D/G 1B was operable and available'during the period in which D/G 1A was inoperable.

The hes1th and safety of the public were not affected by these incidents.

ENCLOSURES 1.

Pane 1 Pneumatic Schematic 2.

Engine Pneumatic Schematic 3.

Calcon Pressure Sensor Model #B4400 l

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D/G 1A Special Report i

General

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The following information is provided in response to the requirements of USNRC Regulatory Guide 1.108 revision 1, section C.3.b.

This regulatory guide section requires that additional narrative material be supplied if the number of failures in the last 100 valid tests is seven or more.

On April 19, 1988 a valid failure occurred on Catawba engine 1A.

This was the seventh valid failure in the last one hundred valid tests for the two Catawba Unit 1 emergen-cy diesel generator sets.

An eighth valid failure, which occurred on April 25, 1988 and a ninth, on May 5, 1988 will also be included in this report.

Reliability Improvement Heasures The following are descriptions and basis for corrective measures, taken or planned, to increase the reliability of the generator units.

a.

The sensors and circuits that can trip the engine during an emergency run will be changed from pneumatic operation to electrical.

These are the engine overspeed trip and the low low lube oil pressure trip. The third (generator fault circuit) is already electrically actuated.

A majority (7 of 9) of the valid failures have involved problems in the pneumatic control system. Converting the emergency trips to QA class 1E components will isolate engine availability during an emergency from pneumatic system problems that have been seen in the past. This modifica-tion is to be completed by the end of the next refueling outage on each unit.

b.

Non-emergency engine protection trip sensors will be replaced with elec-tric or electronic sensors that can provide information to an engine monitoring computer.

A number of past failures can be grouped because of their association with intermittent problems.

This system will trend data from engine sensors and alert responsible parties if abnormalities are noted.

Data will also be collected for troubleshooting intermittent problems which can cause multiple failures before being corrected.

c.

The control panel on the desiccant air dryer will be replaced with a panel designed in house.

The desiccant dryer control panel has demonstrated low reliability and has 1

been out of service frequently because of long replacement lead times and poor vendor support.

The Duke designed panel will allow us the control replacement lead times and make improvements by having control over drawings and material lists.

This system is expected to be installed during the next refueling outages.

Page 1 of 5

s.

d-Manually operated starting air af tercooler condensato dump valves will be replaced with automatic dump valves.

A number of the components removed from the pneumatic control system have been found to have corrosion on the internal parts.

This suggests that the air supply is too moist.

l Operators drain the condensate from the aftercooler on their rounds twice a shift.

During the summer or if the starting air system is used more frequently, the condensata can flood the starting air piping.

If ths water reaches the desiceant towers and wees the desiccant, ineffective.

it is rendered More frequent operator action does not take into account fluctuations in system demand and changes in relative humidity.

dump valves should improve starting air systen reliability by improving Automatic air quality.

Fuel coalescers will be added to the fuel system between the fuel storage e.

tanks and the day tanks.

Engine 1A has suffered 3 valid failures due to clogged fuel strainers Other engines show significant amounts of foreign material (grit, sand metal shavings, paper, man made fibers) in the bottom of the day tanks.

While'the day tanks are cleaned each refueling outage, a more continuous means of preventing this sediment from reaching the strainers will assure greater engine reliability, f.

Procedural changes will be made to enhance engine reliability.

1.

Preventat.ive maintenance on the starting air system desiccant drying towers, which includes desiccant change out, will be performed semi-annually rather than annually to enhance air quality, j

2.

Operators tours of the diesel rooms will include a check to see that the generator control cabinet fans are operating to prevent over-heating of the diodes and rectifiers inside.

3.

Starting air (VG) system dew point will be monitored monthly rather than quarterly to provide better information on VG system reliabili-ty.

This will continue until automatic monitoring is established.

4.

Surveillances on the Calcon sensors will be increased from 18 m to a 6 month frequency.

corrosion exists on the sensorfs' internals. Included in this will be steps to ve Engine Reliability Assessment of the 100 valid tests conducted previous to and including the seventh (April 19, 1988) failure, engine 1A suffered 5 failures in 35 tests and engine IB suffered 2 failures in 65 tests.

(April 25, 1988)

Counting back 100 valid tests from the eighth had 2 failures in 64 tests.failu,re, engine 1A had 6 failures in 36 tests and engine IB 1A had 7 failures in 40 tests and engine IB had 2 in 60.At the ninth valid failure (Ma Page 2 of 5

l 1

Two different approaches can be used to evaluate the reliability. One approach treats each diesel as having a separate failure rate. The failure rate for each engine is calculated and the two rates are then combined to give a reli-ability for the sy' stem.

Using this approach engine 1A has a mean failure rate of 0.1428 or 85.72% reli-ability at a 50% confidence level.

Engine IB has a mean failure rate of 0.0307 or 96.93% reliability.

The reliability of the system, or of at least having one of the two engines operate successfully is the product of the two failure rates subtracted from unity.

This results in a mean reliability rate of 0.9956 or 99.56% reliable with a 50% confidence level.

The second method treats both engines as having an average failure rate of 7 out of a hundred tests or each is 93% reliable. The reliability using this method is between 0.99063 and 0.99742 with a 50% confidence level and a mean of 0.99510 or 99.5% reliable.

l Both methods yield values that exceed the 0.99 reliability goal at a 50%

confidence level established by NUREG75/087 appendix 7-A.

For the eighth valid failure, IA had 6 failures in 36 tests with a mean reli-ability of 83.33%.

1B had 2 failures in 64 tests with a mean reliability of 96.87%. The combined reliability for the engine pair is 99.48% at a 50%

confidence level.

For the ninth valid failure, 1A had 7 failures in 40 tests with a mean reli-ability of 82.53%.

1B had 2 failures in 60 tests with a mean reliability of 96.66%.

The combined reliability for the engine pair is 99.42% at a 50%

confidence level.

l Basis for Continued Operation The plant will continue to be operated because the reliability of electric power to the engineered safety feature equipment exceeds the goal required by regulations and stringent programs are in place to improve engine reliability beyond this goal.

The engines have suffered no further failures since the correction of tha manufacturing tolerences on the Calcon pressure sensors after the 5/5/88 valid failure.

Summary of Tests The Catawba Technical Specifications currently require that the diesel engine j

operability test (PT/1/A/4350/02A) be performed once every 31 days if four j

valid failures (VF) or less have occurred in the last 100 valid attempts AND if one valid failure (VF) or less has occurred in the last 20 valid attempts otherwise, testing will be performed weekly.

Attached is a summary of the start attempts for engines 1A and IB.

"Valid Attempt Number" is a counting of the most recent 100 valid successes (VS) or valid failures (VF) for the Unit 1 engines combined.

"Engine Start Number (s)" are assigned to each engine start and are recorded together with other information about each run, in the control room log books.

The numbers began when the engines were first declared operable at Catawba.

Page 3 of 5 i

"Test Result" is one of four possible codes, VS, IT, IF or VF VS stands for valid success.

all of the following conditions must be metsFor a test to be considered a valid success "

The diesel engine starts and 4.ccelerates to at 441 RPM (greater than or equal to 98% speed) greater than or equal to within 11 seconds.

b D/G voltage and frequency shall be at least 4160 plus or minus 420 volts and 60 plus or minus 1.2 He within 11 seconds af ter start

signal, The D/G is successfully loaded to greater than or equal to 2875 KW c

(50% continuous rating) and operates at this load for at least one hour.

di D/G shutdown was not due to an abnormal condition that w ultimately resulted in D/G damage or failure.

IT stands for an "invalid test".

of the conditions described above for VS are not met due to an intent shutdown prior to loading or operating for greater than one hour at 2875 KW better that'was not due to an abnormal condition that would ha or resulted in D/G damage or failure.

mately IF stands for an "invalid failure".

If any of the met AND the test is not an IT as described AND if any of the following con tions are met, the test in considered an IF.

Operator error,

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b Spurious operation of a trip that is bypassed in the emergency operating mode, operating mode or is not part of the defined D/G u c

di The failure occurs during the process of trouble shooting, The failure occurs during the process of a functional check out prio et to returning the D/G to service following maintenance l

r Note:

The Functional Check Out should, be perforned prior to and independ o_,f the Operability Test which is performed for the purpose of decl ent ing operability.

failure for reasons other than those listed above is conside ar-VALID FAILURE.

Page 4 of 5

tands for "valid failure".

following conditions are true,A test is considered a valid failure if any of The test cannot be classified as a VS, IT, or IF as described as

above, b

that would have ultimately resulted in D/G darnage or f i a condition a ure, Performance of a cranking or venting procedure leads to the di c:

of a condition (such as excessive water or oil in a cylinder) that scovery would result in engine failure during operation.

s, 126 IT's, and 0 IF during the 99 valid tests precedin valid failure.

s, r

4 Page 5 of 5

D/G 1A Test Data L11d Engine 1A Engine IB

tempt Start Test Test Start Test Test Lmber Number Result Date Number Result Date 07 700 VS 5/17/88 16 796 VS 5/15/88 15 699 VS 5/14/88 l-4 698 VS 5/13/88 697 IT 5/13/88 13 795 VS 5/12/88 12 794 VS 5/12/88 793 IT 5/12/88 792 IT 5/12/88 11 696 VS 5/8/88 695 IT 5/8/88 694 IT 5/8/88 10 791 VS 5/6/88 693.

IF 5/5/88 i

692 VF 5/5/88 1

790 VS 5/4/88 691 VS 5/3/88 i

789 VS 4/30/88 788 IT 4/30/88 787 IT 4/30/88 786 IT 4/30/88 i

690 VS 4/29/88 6

689 V3 4/27/88 688 IT 4/27/88 687 IT 4/27/88 686 IT 4/27/88 685 IT 4/27/88 l

785 VS 4/26/88 684 VS 4/25/88 683 IT 4/25/88 682 IT 4/25/88 681 IT 4/25/88 680 IT 4/25/88 679 IF 4/25/88 678 IF 4/25/88 677 IF 4/25/88 676 VF 4/25/88 784 VS 4/24/88 675 VS 4/23/88 674 VS 4/21/88 673 IT 4/21/88 672 IT 4/21/88 671 IT 4/21/88 670 IT 4/21/88 669 IT 4/21/88 783 VS 4/19/88 668 IT 4/19/88 667 IT 4/19/88 666 IT 4/19/88 665 IT 4/19/88 664 IT 4/19/88 page 1 of 8 -

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' gna Valid Engine 1A Engine IB Attempt Start Test Test Start Test Test Number Number Result.

Date Number Result Date IT 4/19/88 663 86 662 VF 4/19/88 85 782 VS

'4/18/88 84 781 VS 4/13/88 83 780 VS 4/13/88 82 661 VS 4/12/88 660 IT 4/12/88 659 IT 4/12/88 658 IT 4/12/88 657 IT 4/12/88 656 IT 4/12/88 655 IT 4/12/88 654 IT 4/12/88 653 IF 4/12/88 81 652 VF 4/12/88 80 651 VS 4/6/88 79 779 VS 4/6/88 78 778 VS 3/30/88 650 IT 3/29/88 649 IT 3/29/88 648 IT 3/29/88 77 647 VS 3/29/88 76 777 VS 3/28/88 75 646 VS 3/23/88 645 IT 3/22/88 644 IT 3/22/88 643 IT 3/22/88 642 IT 3/22/88 641 IT 3/22/88 640 IT 3/22/88 639 IT 3/22/88 638 IT 3/22/88 637 IT 3/22/88 636 IT 3/22/88 635 IT 3/12/88 634 IT 3/22/88 633 IT 3/22/88 74 776 VS 3/22/88 73 632 VS 3/22/88 72 631 VF 3/22/88

~.' s VS 3/21/88 71

/

774 IT 3/21/88 70 773 VS 3/13/88 69 630 VS 3/8/88 68 772 VS 3/8/88 629 IF 3/8/88 628 IF 3/8/88 67 627 VF 3/7/88 (IA start 627 changed to "VF" from "IF" during NRC audit on 5/17/88) 626 IT 3/7/88 625 IT 3/7/88 page 2 of 8 -

/

o Valid Engine '1A Engine IB Attempt Start Test Test Start Test Test Number Number Result Date Number Result Date IT 3/7/88 624 l

66 623 VF 3/7/88 65 771 VS 3/6/88 64 770 VS 2/29/88 63 769 VS 2/22/88 768 IT 2/22/88 62 767 VS 2/15/88 61 766 VS 2/10/88 60 622 VS 2/8/88 59 765 VS 2/5/88 58 764 VS 1/31/88 57 763 VS 1/25/88 762 IT 1/23/88 621 IT 1/23/88 56 761 VS 1/17/88 55 620 VS 1/13/88 54 619 V5 1/11/88 53 760 VS 1/9/88 52 759 VS 1/3/88 51 758 VS 12/28/87 50 757 VS 12/21/87 49 618 VS 12/15/87 617 IT 12/15/87 616 IT 12/15/87 615 IT 12/15/87 614 IT 12/15/87 613 IT 12/15/87 48 756 VS 12/14/87 47 755 VS 12/11/87 46 754 VS 12/5/87 753 IT 12/5/87 752 IT 12/5/87 751 IT 12/5/87 750 IT 12/5/87 749 IT 12/5/87 748 IT 12/3/87 747 IT 12/3/87 746 IT 12/3/87 745 IT 12/3/87 744 IT 12/3/87 743 IT 12/3/87 742 IT 12/3/87 741 IT 12/3/87 740 IT 12/3/87 739 IT 12/3/87 738 IT 12/3/87 737 IT 12/3/87 736 IT 12/3/87 735 IT 12/3/87 734 IT 12/3/87 733 IT 12/3/87 page 3 of 8 -

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Valid 5.ngine '1A Engine IB Attempt Start Test Test Start Test Test Number Number Result Date Number Result.

Date 732 IT 12/3/87 731 IT 12/3/87 730 IT 12/3/87 729 IT 12/3/87 728 IT 12/2/87 727 IT 12/1/87 726 IT 12/1/87 45 725 VS 12/1/87 724 1T 12/1/87 723 IT 12/1/87 722 IT 12/1/87 721 IT 12/1/87 720 IT 12/1/87 l

44 719 VF 12/1/87

)

718 IT 11/30/87 717 IT 11/25/87 l

43 612 VS 11/21/87 611 IT 11/20/87 610 IT 11/70/87 1

609 IT 11/20/87 608 IT 11/20/87 607 IT 11/20/87 606 IT 11/20/87 605 IT 11/20/87 604 IT 11/20/87 603 IT 11/20/87 602 IT 11/20/87 601 IT 11/20/87 600 IT 11/?.0/87 599 IT 11/20/87 598 IT 11/20/87 597 IT 11/20/87 596 IT 11/20/87 595 IT 11/20/87 594 IT 11/20/87 593 IT 11/20/87 592 IT 11/20/87 591 IT 11/20/87 590 IT 11/20/87 589 IT 11/20/87 588 IT 11/20/87 587 IT 11/20/87 586 IT 11/20/87 585 IT 11/20/87 584 IT 11/20/87 583 IT 11/20/87 582 IT 11/20/87 581 IT 11/20/87 580 IT 11/20/87 579 IT 11/20/87 578 IT 11/20/87 page 4 of 8 -

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'y<s Valid Engine 1A Engine IB Attempt Start Test Test Start Test Test Number Number Result Date Number Result Date 577 IT 11/20/87 576 IT 11/19/87 575 IT 11/19/87 574 IT 11/19/87 573 IT 11/19/87 572 IT 11/19/87 571 IT 11/19/87 570 IT 11/19/87 569 IT 11/19/87 568 IT 11/19/87 567 IT 11/18/87 566 IT 11/18/87 565 IT 11/18/87 564 IT 11/18/87 563 IT 11/18/87 562 IT 11/18/87 561 IT 11/18/87 560 IT 11/18/87 716 IT 11/17/87 559 IT 11/16/87 558 IT 11/15/87 557 IT 11/15/87 556 IT 11/15/87 555 IT 11/15/87 42 554 VS 11/14/87 553 IT 11/14/87 552 IT 11/14/87 551 IT 11/14/87 550 IT 11/13/87 549 IT 11/13/87 548 IF 11/13/87 547 IT 11/13/87 715 IT 11/1/87 41 714 VS 10/29/87 713 IT 10/29/87 712 IT 10/29/87 711 IT 10/29/87 710 IT 10/29/87 709 IT 10/29/87 708 IT 10/29/87 707 IT 10/29/87 706 IT 10/29/87 705 IT 10/29/87 704 IT 10/29/87 703 IT 10/29/87 702 IT 10/29/87 701 IT 10/29/87 700 IT 10/29/87 699 IT 10/29/87 698 IT 10/29/87 697 IT 10/29/87 page 5 of 8 -

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Valid Engine 1A Engine IB Attempt Start Test Test Start Test Test Number Number Result Date Number Result Date 696 IT 10/29/87 695 IT 10/29/87 694 IT 10/29/87 693 IT 10/29/87 692 IT 10/29/87 691 IT 10/29/87 690 IT 10/29/87 689 IT 10/29/07 688 IT 10/29/87 687 IT 10/29/87 686 IT 10/28/87 685 IT 10/28/87 684 IT 10/28/87 683 IT 10/28/87 682 IT 10/28/87 681 IT 10/28/87 680 IT 10/28/87 679 IT 10/28/87 678 IT 10/28/87 677 IT 10/28/87 676 IT 10/28/87 675 IT 10/28/87 674 IT 10/28/87 673 IT 10/28/87 672 IT 10/28/87 671 IT 10/27/87 670 IT 10/27/87 669 IT 10/27/87 668 IT 10/27/87 667 IT 10/27/87 666 IT 10/27/87 665 IT 10/27/87 664 IT 10/27/87 663 IT 10/27/87 662 IT 10/26/87 661 IT 10/26/87 660 IT 10/26/87 659 IT 10/26/87 658 IT 10/26/87 657 IT 10/26/87 656 IT 10/26/87 655 IT 10/26/87 40 654 VS 10/26/87 653 IT 10/24/87 652 IT 10/10/87 651 IT 10/9/87 39 650 VS 10/9/87 38 649 VS 10/9/87 648 IT 10/8/87 647 IT 10/8/87 646 IT 10/8/87 page 6 of 8 -

n, J.-

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N Valid.

Engine 1A -

Engine IB Attempt Start Test Test Start Test Test Number Number Result Date Number Result Date 645 IT 10/8/87 l

644 IT 10/d/87 643 IT 10/8/87 642 IT 10/8/87 641 IT 10/8/87 37 640 VF 10/7/87 36 639 VS 10/7/87 638 IT 10/7/87 35 637 VS 10/6/87 546 IT.

10/6/87 545 IT 10/6/87 636 IT 10/6/87 544 IT 10/5/37 34 543 VS 10/4/87 33 542 VS 10/1/87 635 IT 9/14/87 32 634 VS 9/14/87 31 541 VS 9/9/87 30 633 VS 9/8/87 29 632 VS 8/30/87 28 631 VS 8/24/87 27 630 VS 8/17/87 26 540 VS 8/11/87 25 629 VS 8/10/87 539 IT 8/4/87 24 628 VS 8/3/87 627 IT 8/3/87 23 626 VS 7/16/67 22 538 VS 7/13/87 21 625 VS 6/28/87 20 537 VS 6/19/87 19 624 VS 6/9/87 18 536 VS 6/5/87 535 IT 6/5/87 17 534 VS 6/3/87 16 623 VS 6/1/87 622 IT

'6/1/87 15 533 VS 5/27/87 14 532 VS 5/20/87 13 621 VS 5/8/87 12 531 VS 5/7/87 530 IT 5/7/87 529 IT 5/7/87 528 IT 5/7/87 11 620 VS 4/27/87 10 527 VS 4/24/87 9

619 VS 4/22/87 8

526 VS 4/13/87 7

618 VS 3/30/87 6

617 VS 3/30/87 5

525 VS 3/26/87 page 7 of 8 -

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Valid' Engine 1A Engine IB Attempt Start Test Test Start Test Test Number Number Result Date Number Result Date j

4 616 VS

'3/23/87 3

2 615 VS 3/16/87 614 VS 3/9/87 613 IT 3/8/87 612 IT 3/8/87 611 IT 3/8/87 610 IT 3/8/87 609 IT 3/7/87 1

524 VS 3/5/87 0

608 VS 3/4/87 607 IT 3/4/87 606 IT 3/2/87 605 IT 2/23/87 t

(1) 604 IT 2/23/87 603 VS 2/23/87 523 IT 2/17/87 522 IT 2/17/87 (2) i 602 VS 2/16/87 521 IT 2/13/87 (3)

(4) 601 VS 2/9/87 600 VS 2/2/87 (5) 520 VS 1/28/87 (6) 599 VS 1/28/87 519 IT 1/28/87 518 IT 1/28/87 (7) 598 VS 1/22/87 597 IT 1/22/87 596 IT 1/22/87 (8) 595 IT 1/22/87 594 VS 1/13/87 (9) 517 VS 1/9/37 516 IT 1/9/81 515 IT 1/9/87 (10) 593 VS 1/9/87 (11) 514 VS 12/30/86 (12)

(13) 592 VS 12/29/86 591 VS 12/22/86 590 IT 12/22/86 513 IT 12/16/86 (14) 589 VS 12/15/86 page 8 of 8 -

.