ML20138B474
| ML20138B474 | |
| Person / Time | |
|---|---|
| Site: | McGuire  |
| Issue date: | 11/21/1985 |
| From: | Tucker H DUKE POWER CO. |
| To: | Grace J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| NUDOCS 8512120305 | |
| Download: ML20138B474 (3) | |
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November 23.i985 i
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o-r Dr. J. Ne E'a firace, Regional Administrator U. S. Nubleap Ret,'alatory Commission - Region II r
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Subject:
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Dqcket No. 50-369 Dihel Generator Failur'e 4,
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e In accoIdance with McGuire Nuclear Stat' ion's Technical Specifications 4.8.1.1.3 and 6.9.1, attached isa report of invalid' Diesel Generator (D/G) failures which
-oc Crred at McGuire on October 2Y. P.9, and 30, 1985' during festing and trouble-chooting 'of 'the Diebel Generator".' -
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ad no impact on the hhlth and,sihty of the public.
The event
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i DUKE POWER COMPANY McGUIRE NUCLEAR STATION D/G 1B Invalid Failures Due to Low Crankcase Vacuum Diesel Generator (D/G) IB experienced three invalid failures on October 22, 1985, at 0053, 0114, and 0231. The first invalid failure occurred as a result of a low crankcase vacuum trip while D/G 1B operability was being verified, after repairs on cylinder 8 left (8L). Attempts to reseal and test the cover of cylinder 8L resulted in two other invalid failures from low crankcase vacuum trips. D/G 1B was started and operated successfully following these repairs and the problem appeared to be resolved.
However, D/G 1B experienced three additional invalid failures due to low crankcase vacuum trips:
two on October 29, 1985, at 1003 and 1451, and one on October 30, 1985, at 0117. The first invalid failure on October 29 occurred while the operability test was being performed. The two start attempts following this failure were.for troubleshooting purposes. During troubleshooting, it was discovered that the rubber coupling seal of the main lube oil header was allowing oil to spray into the vacuum system. After the geal was replaced, D/G 1B was started and operated successfully.
Unit I was in Mode 1 at 100% power at the time of all incidents.
Background
The purpose of the D/G crankcase vacuum system is to take combustible gases out of the engine crankcase. The system is set up such that an alarm will be given when vacuum decreases to -0.96 inches of water (INWD). Enen the D/G is started in the manual mode, the D/G will trip when -0.5 1NWD is reached.
However, this trip signal is bypassed during an emergency D/G start.
Description of Event On October 22, 1985, at 0053, the operability of D/G 1B was being verified upon completion of maintenance repairs on the cooling water jacket of cylinder 8L.
When D/G 1B experienced two consecutive low crankcase vacuum trips, it was thought the trips were the result of air leaks on cylinder 8L.
After the covers of the cylinder 8L and the lube oil separator were resealed,
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D/G 1B was started and operated successfully. The source of the low crankcase vacuum trips were thought to be air leaks resulting from maintenance repair work.
D/G 1B experienced another low crankcase vacuum trip during an operability test on October 29, 1985, at 1003. An investigation began to determine the cource of the problem. To assist the investigation, a clear plexiglass sight cover was installed on the lube oil separator to observe oil level during cngine operation.
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t When'UfG 1B wa operated with this clear sight cover in place, personnel observed what appeared to be an excessive amount of oil spraying into the vacuum system. To confirm this, a clear sight cover was installe3 on a dif-ferent lube oil separator (D/G 1A) and observed the oil in it due,ing engine operation. 011 was not seen spraying into the D/G 1A vacuum system as they hadpfor the D/G IB vacuum system.
It was discovered that the rubber coupling seal of the main lube oil header was so disintegrated and porous that it allowed oil to be pulled into the vacuum system. This interfered with the vacuum and caused the low crankcase vacuum, trip. The seal was original equipment (1976) on the Unit 1 D/G and had never been replaced. The, seal was replaced.'
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Low crankcase vacuum failures on D/G 1B have been a recurring problem. Prior to the' D/G IB low crankcase, vacuum failures on October 22 and 29, D/G IB had experienced similar low crankcase vacuum failures on August 6, August 27, and September 12, 1985. The cause of these failures could not be determined.
However, these failures may have occurred partially or totally as a result of the,failing coupling seal.
This is not the first case of degraded rubber on a D/C.r D/G 1A has experi-enced invalid failures due to the deterioration of the rubber fuel line hoses.
A commftment was made in the report dated May 23, 1985 to write,a five year preventive paintenance procedure for the D/Gs. The procedure was to include steps to replace all rubber components which are in contact with lube oil or fuel oil.
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CORRECTIVE ACTIONS:
Inmediate:
None Subsequent:
- 1) For the October 22 trip, the covers on cylinder 8L and' the lube oil separacor were resealed. j i 1
- 2) For the October 29 trip, thd operation of the lube oil separator was osserved to determine the source of an erratic crankcase' vacuum.
?) The rubber coup 2Ang sseal of the main lube ' oil header was
' + found to be leaking oil into the vacuum system and was replaced. Replacement seals fottthe other D/G's were ordered.
5 Planned:
- 1) The coupling seals for D/Gs lA, 2A, and 2B will be replaced >
1 when the parts are received.
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A 5 year preventive maintenance procedure will betwritten N
-for the D/Gs.
It will include, among other items, thq' I
replacement of coupling seals of the main lube oil haader, y
SAFETY ANALYSIS:
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The low crankcase vacuum trip signal is bypassed during an emergency D/G start; therefore, D/G operation would not have been affected during an emergency D/G ctart. D/G 1A as well as offsite power were available during this time.
i The health and safety of the public were not affected by this incident.
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