ML20247A810

Special Rept:On 890410,several Invalid Failures of Diesel Generator 2B Occurred.Caused by Air Leak at Tubing Connection to Port 3 of Pneumatic Logic Board.Parts of Pneumatic Control Sys to Be Replaced in Cycle 4 Outage

ML20247A810
Person / Time
Site:	Catawba
Issue date:	05/10/1989
From:	Tucker H DUKE POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 8905230279
Download: ML20247A810 (3)

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, DUKE.Powen GOMPANY P.O. BOX 33189 CHARLOTTE. N.O. 28242

- HAL B. TUCKER Teixemme vum rer.asoster (704) 073 4 531 attMILEAlt PROptlUTION

May 10,.1989.

. Document Control Desk. I

~U. S.. Nuclear' Regulatory Commission-  !

. Washington,'D.'C. 20555  !

1

. Subj ect: -Catawba. Nuclear Station, Unit 2 Docket No. 50-414 Special'. Report Gentlemen:

I Pursuant to Technical' Specifications 6.9.2 and 4.8.1.1, please find attached a.

2 Special Report-concerning several Diesel Generator 2B invalid failures.on April 10,.1989.-The invalid failures were caused by tubing leaks during the Unit-2 end

.of cycle'2 refueling. outage Diesel Generator 2B break-in runs. j Very truly yours,

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~Hal B.' Tucker l

'JGT/3/IIR89-32 xc: Mr. S. D. Ebneter Regional Administrator, Region-II-U. S.. Nuclear Regulatory Commission i

101 Marietta Street, NW, Suite 2900

> Atlanta, Georgia -30323 l

Mr.'W. T.. Orders )

NRC Resident Inspector 1 Catawba Nuclear Station pmmum g

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l) b SPECIAL REPORT

'l CATAWBA NUCLEAR STATION, UNIT 2 DIESEL GENERATOR 2B INVALID FAILURES y

i DUE TO TUBING LEAK DURING BREAK-IN RUNS i.

I: .Several invalid failures of Diesel Generator (D/G) 2B occurred on April 10, '

1989 during the ' Catawba Nuclear Station Unit 2 end of cycle 2 refueling outage. D/G 2B had not been returned to service following its required outage

l. . inspection and teardown at the' time these failures occurred. D/G 2B was on a

[ monthly test frequency prior to the engine inspection being performed. There have been 0 valid failures in the last 20 valid tests and 2 valid failures in the last 100 valid tests on D/G 2B.

After the inspection of D/G 2B was completed, a series of break-in runs were required to ensure the complete reliability of the engine prior to its being rettrned to service. In conjunction with these break-in runs, modification

'NSM CN-20486, which replaced the pneumatic emergency trip instrumentation (Lo to Aube oil and overspeed) with electronic trip instrumentation, was to be tes;ed to ensure it. functioned properly. On the first 6 start attempts

'following the engine inspection (start attempt Nos. 532 through 537), the 0/G tripped after running approximately 60 seconds.

On April 10, 1989, at 1655 hours0.0192 days <br />0.46 hours <br />0.00274 weeks <br />6.297275e-4 months <br />, start attempt #532 was performed on D/G 2B

-for Mechanical Maintenance's first break-in run. After the engine started and came up to speed, it was observed on the gauges mounted on the pneumatic sensor tubing lines that control air pressure was only increasing to approxi-mately 10 psig. These lines should increase to the system air pressure of 60 psig after all sensors stop venting when engine parameters are at normal operating conditions. After the 60 second group II lockout period was com-plete, the engine tripped as designed due to these low pressures. It was obvious that pressure was being lost either by an air leak or a pneumatic component malfunctioning, but the exact location of the problem was very difficult to detect. In order to pinpoint the source of this pressure loss, the 0/G had to be run to allow Instrumentation and Electrical (IAE) an oppor-tunity to troubleshoot the system. Various parts of the pneumatic control system such as the engine mounted calcon sensors, several components on the pneumatic logic board, the tubing to the engine sensors, and the tubing in the engine control panel were checked for leaks or improper venting during the next several engine starts. An air leak was finally discovered at the tubing

. connection to port 3 of the pneumatic logic board. Investigation revealed that the fitting had apparently been improperly tightened during its last connection. The connection was remade and the engine started and ran with no prc'clems being observed.

Because only 60 seconds were allowed to troubleshoot the source of the pres-sure loss before the engine tripped, six starts had to be performed before the leak was found. The large amount of tubing and pneumatic components that could have been causing this type of failure also contributed to the number of engine starts required before the problem was discovered. Because control air L - _ _ _--- - _ _ ___ ______J

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pressure to the group II pneumatic sensors is metered through a .028 inch l orifice, even a small leak such as the one discovered can prevent pressure  !

from being established in the system. Due to the maintenance performed on  ;

this. system.during the outage, it is possible this fitting had been discon-

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nected, then. improperly reconnected. The purpose of break-in runs and other j l D/G testing after outage related maintenance is to. discover these types of

! problems prior to the engine being declared operable.

On April 12,1989, all D/G 2B' testing was satisfactorily completed and it was declared operable. The remainder of the D/G pneumatic control system is scheduled to be replaced during the Unit 2 end of cycle 4 refueling outage l with an electronic system per modification NSM CN-2052B. j i

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