Information Notice No. 91-62: Diesel Engine Damage caused by Hydraulic Lockup Resulting from Fluid Leakage into Cylinders

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                             WASHINGTON, D.C.  20555

                               September 30, 1991

                               LOCKUP RESULTING FROM FLUID LEAKAGE INTO 


All holders of operating licenses or construction permits for nuclear power 


The U.S. Nuclear Regulatory Commission (NRC) is issuing this information 
notice to alert addressees to the possibility of severe damage to the 
emergency diesel generator (EDG) engine caused by hydraulic lockup resulting 
from fluid which has leaked into cylinders of the diesel engine.  It is 
expected that recipients will review the information for applicability to 
their facilities and consider actions, as appropriate, to avoid similar 
problems.  However, suggestions contained in this information notice are not 
NRC requirements; therefore, no specific action or written response is 

Description of Circumstances

On June 16, 1991, during a precautionary check in preparation for a routine 
surveillance test of a Unit 2 emergency diesel generator (EDG), Southern 
California Edison, the licensee at the San Onofre Nuclear Generating 
Station, found several pints of water in an engine cylinder.  This 
precautionary check allowed the licensee to avert severe engine damage.  The 
licensee immediately stopped the surveillance, declared the EDG inoperable, 
and initiated a work order to determine the cause.  After removing the 
cylinder module, the licensee found that a small leak path had slowly 
developed on the head gasket, allowing the jacket cooling water to intrude 
into the cylinder.  The licensee had operated this engine 7 days earlier 
without difficulty.  Apparently, a sufficient amount of fluid had leaked 
after this previous test to partially fill the cylinder with water.  The 
licensee determined that if the EDG had been 

                                                       IN 91-62
                                                       September 30, 1991
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started on this occasion without first being checked for water in the cylin-
ders, the EDG would have been severely damaged by hydraulic lockup of the 
cylinder.  While performing a similar precautionary check in 1987, the 
licensee discovered a similar condition on a Unit 1 EDG that was caused by a 
cracked cylinder.  Furthermore, an EDG at the Palo Verde Nuclear Generating 
Station was severely damaged in 1986 because it was started after water 
leaked into a cylinder through a cracked cylinder wall.


Because of the incompressible nature of water and fuel oil, the presence of 
significant amounts of fluid in an engine cylinder can cause hydraulic 
lockup during the compression stroke.  When the force from the starter and 
other firing cylinders tries to overcome this lockup, the engine could be 
severely damaged.  The fluid can come from a number of sources such as a 
leaking head gasket, a cracked cylinder or head, or a defective fuel 
injector or lube oil system.  EDG vendors such as Transamerica Delaval, 
Incorporated (TDI Instruction Manual, Volume 1, Model DSRV-20-4 Diesel 
Engine/Generator, page 4-2) and the General Motors Company, Electro-Motive 
Division (GM/EMD Scheduled Maintenance Program, Stationary Power Units with 
Turbocharged Engines, Maintenance Instruction 1728, Revision C, November 
1977), have recognized the significance of this hazard and have recommended 
that their clients first check for fluid in the cylinders before starting 
the engine if the engine has been shut down and cooled for a prolonged 
period.  The NRC has discussed this problem with experienced diesel engine 
operators and understands that this is also a common practice in non-nuclear 

To prepare the engine for each surveillance start, the operators at San 
Onofre lock out the engine's automatic-start feature, open the indicator 
petcocks (test valves) on all cylinders, and rotate the engine slowly to 
check for fluid in the cylinders.  After verifying the absence of fluid in 
the cylinders, the operators start the EDG.  The NRC conducted an informal 
survey of resident inspectors at plants of other NRC licensees and found 
that not all NRC licensees are following this practice, possibly because the 
EDG becomes temporarily inoperable while it is locked out with the cylinder 
petcocks open.  

The NRC has also addressed this issue in its "Safety Evaluation Report 
Related to the Operability and Reliability of Emergency Diesel Generators 
Manufactured by Transamerica Delaval, Inc.," NUREG-1216, August 1986, 
beginning on page B-4, and in a contract study "Review of Resolution of 
Known Problems in Engine Components for Transamerica Delaval Inc. Emergency 
Diesel Generators," PNL-5600, December 1985, on page 4.160.  These documents 
are available in the NRC Public Document Room at 2120 L Street N.W., 
Washington, D.C.  20555.


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This information notice requires no specific action or written response.  If 
you have any questions about the information in this notice, please contact 
one of the technical contacts listed below or the appropriate Office of 
Nuclear Reactor Regulation project manager. 

                                   Charles E. Rossi, Director
                                   Division of Operational Events Assessment
                                   Office of Nuclear Reactor Regulation

Technical contacts:  Andrew Hon, RV
                     (714) 492-2641

                     Peter Prescott, NRR
                     (301) 492-1011

                     Vern Hodge, NRR
                     (301) 492-1861

Attachment:  List of Recently Issued NRC Information Notices

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