IE Circular No. 79-12, Potential Diesel Generator Turbocharger Problem


                               June 21, 1979 

MEMORANDUM FOR:     B. H. Grier, Director, Region I 
                    J. P. O'Reilly, Director, Region II 
                    J. G. Keppler, Director, Region III 
                    K. V. Seyfrit, Director, Region IV 
                    R. H. Engelken, Director, Region V 

FROM:               Norman C. Moseley, Director, Division of Reactor 
                      Operations Inspection, IE 

                    TURBOCHARGER PROBLEM 

The subject Circular is transmitted for issuance on June 28, 1979.  The 
Circular should be issued to all power reactor operating facilities and all 
utilities having a construction permit.  Issuance of the Circular is based 
on information obtained from Monticello Nuclear Generating Station which 
indicated the Electro-Motive Division of General Motors diesel engines have 
a potentially generic probelm in the lubricating oil system which could 
eventually  failure of the turbocharger. 

The text of the Circular and draft letter to the licensees and permit 
holders are enclosed for this purpose. 

                              Norman C. Moseley, Director 
                              Division of Reactor Operations Inspection 
                              Office of Inspection and Enforcement 

1.   Draft Transmittal Letter
2.   IE Circular No. 79-12

CONTACT:  V. D. Thomas, IE 

(Draft transmittal letter for IE Circular 79-12, to each holder of an 
Operating License or a Construction Permit.) 

                                                      IE Circular No. 79-12 


The enclosed IE Circular No. 79-12, is forwarded to you for information. No 
written response is required. Should you have any questions related to your 
understanding of this matter, please contact this office. 


                                        (Regional Director) 

1.   IE Circular No. 79-12 
2.   List of IE Circulars 
       Issued in Last 12 

                             UNITED STATES 
                          WASHINGTON, D.C. 20555 
                              June 28, 1979 

                                                      IE Circular No. 79-12 


Description of Circumstances: 

The Electro-Motive Division (EMD) of General Motors Corporation has recently
identified a potential failure mode of turbochargers used on EMD diesels in 
nuclear plant standby service. 

When an engine is in the normal standby mode, the lubricating oil 
temperature is maintained at about 115 degrees F and the circulating oil 
pump supplies warm oil to the turbocharger bearings at a flow rate of about 
2 gpm. Since the total oil pump flow rate is 6 gpm, 4 gpm is also 
circulated, via a 30 psi relief valve, through the lube oil filter and 
cooler which serves to keep the entire accessory lubricating oil system 
primed to support a fast start. If a power outage occurs, the oil 
circulating pump may stop 5 to 10 seconds before the engine receives a start 
signal; but the main bearing and piston cooling pump will immediately 
receive oil from the primed lube oil filter-cooler system thus providing a 
rapid buildup of engine lube oil pressure throughout the engine bearing and 
turbocharger systems. 

A potential problem occurs, however, if the diesel engine receives a repeat 
rapid start within a minimum of 15 minutes and a maximum of 3 hours after a 
shutdown from a previous run in which the engine has reached full operating 
temperature. If, for example, the engine had been operated for about 1 hour 
at full load, the lube oil temperature would be at about 200 degrees F at 
time of shutdown. Under these circumstances, the full 6 gpm output of the 
circulating pump will flow only to the turbocharger bearings because of the 
lower viscosity of the hot lubricant. At this temperature, the circulating 
pump pressure will not reach 30 psi. Until the lube oil cools to about 160 
degrees F, no oil will be supplied via the relief valve to the equipment 
rack for the first 2 to 3 hours after engine shutdown. During this cooling 
period some of the oil contained in the cooler and filter will drain back to 
the engine sump via the lube oil scavenging pump, and some of the oil from 
the strainer box will be drawn into the cooler by the system vacuum that 
develops. The result is that when a repeat fast start occurs within the 
above 15 minute to 3 hour time frame after a hot shutdown, lack of prime oil 
system pressure can cause engine damage. In the worst case of a repeat fast 
start, the engine may actually reach operating speed, 900 RPM, before the 
required oil pressure is established at the turbocharger thrust bearing. 
This may cause some smearing of the bearing metal so that cumulative damage 
from several similar starts would result in a turbocharger failure. 

IE Circular No. 79-12                                      June 28, 1979 
                                                            Page 2 of 2 

EMD is currently developing a modification to improve the lube oil system. 
It is planned that this modification will be available for installation in 
approximately 6 months. In the interim, the following actions are 
recommended for those having EMD diesel engines: 

1.   Repeated fast hot starts within a minimum 15 minute to 3 hour time 
     frame after shutdown should be avoided. Allow the engine to cool at 
     least 3 hours after it has been operated in the "loaded" mode, or 
     otherwise a restart should be performed within 15 minutes of shutdown. 
2.   After changing oil filter elements or draining the accessory oil system
     for any reason, and upon refilling of the system make sure that the 
     circulating oil pump is in operation for at least 30 minutes and that 
     the strainer box is full before starting engine. The engine should then
     be brought to an idling condition to assure complete filling of 
     accessories before any subsequent fast start is made. 

3.   Any small leak at the top of the oil cooler should be corrected. A leak
     at this location allows air to be drawn into the cooler during 
     shutdown, which will cause the drain back to be more rapid. 

4.   Avoid testing of the redundant diesel engines concurrently. Where it is
     necessary to run the redundant diesels concurrently, maintain one 
     diesel in the running mode for a minimum of 3 hours following the 
     shutdown of the other. 

No written response to this Circular is required. If you require additional 
information regarding this subject, contact the Director of the appropriate 
NRC Regional Office. 


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