IE Circular No. 79-12, Potential Diesel Generator Turbocharger Problem
CR79012 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 SUBJECT: IE CIRCULAR NO. 79-12, POTENTIAL DIESEL GENERATOR 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 Enclosures: 1. Draft Transmittal Letter 2. IE Circular No. 79-12 CONTACT: V. D. Thomas, IE 49-28180 . (Draft transmittal letter for IE Circular 79-12, to each holder of an Operating License or a Construction Permit.) IE Circular No. 79-12 Addressee: 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. Sincerely, Signature (Regional Director) Enclosures: 1. IE Circular No. 79-12 2. List of IE Circulars Issued in Last 12 Months . UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 June 28, 1979 IE Circular No. 79-12 POTENTIAL DIESEL GENERATOR TURBOCHARGER PROBLEM 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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