United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 84-92: Cracking of Flywheels on Cummins Fire Pump Diesel Engines

                                                         SSINS No.:  6835  
                                                         IN 84-92          

                               UNITED STATES 
                       NUCLEAR REGULATORY COMMISSION 
                    OFFICE OF INSPECTION AND ENFORCEMENT 
                          WASHINGTON, D.C. 20555  

                              December 17, 1984

Information Notice No. 84-92:   CRACKING OF FLYWHEELS ON CUMMINS FIRE 
                                   PUMP DIESEL ENGINES 

Addressees: 

All nuclear power reactor facilities holding an operating license (OL) or 
construction permit (CP), research and test reactors, and fuel facilities. 

Purpose: 

This information notice is to alert recipients of a potentially significant 
problem of cracking flywheels on certain models of Cummins fire pump diesel 
engines. This cracking apparently becomes noticeable only after it has 
propagated through the thickness of the flywheel and appears on its outer 
surface. It is expected that recipients will review the information for 
applicability to their facilities and consider actions, if appropriate, to 
preclude similar problems occurring at their facilities. However, 
suggestions contained in this information notice do not constitute NRC 
requirements; therefore, no specific action or written response is required.

Description of Circumstances 

Since December 12, 1983, LaSalle County Station has experienced repeated 
fatigue cracking of flywheels on both of its Peerless Pump Co. fire pump 
diesel engines, Cummins Model No. NT-855-F2 equipped with flywheel Part No. 
3453 (assembly no. 3023676). The cracks appear to initiate on the engine 
side (blind side) of the flywheel at a circumferential groove which 
intersects each crank shaft attachment bolt hole. Cracks have been found to 
initiate after as little as 34 hours of operation, but can only be detected 
with the use of a liquid penetrant. The initial development of these cracks 
is fast, but subsequent growth is slower and there have been no catastrophic 
failures to date. The cracking is believed to be related to the response of 
the flywheel to inherent engine and gearbox vibration and it appears to be 
generic to the flywheel design. 

This problem was first discovered when a flywheel on an engine with 850 
hours of operation had cracked through its thickness over 360 of the 
circumferential groove. A second unit with approximately 1500 hours of 
operation was found to have had its flywheel cracked through its thickness 
over approximately 270 of the circumferential groove. Both flywheels 
were replaced and a 6-month inspection program was established. At the end 
of the first 6-month period, a surface penetrant test was used and cracks 
were discovered on the engine side of the flywheels on both units (one unit 
with 34 hours of operation and the other with 50 hours). At this point it 
was decided to establish a program to inspect the flywheels after 50 hours 
of operation. 


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                                                       IN 84-92           
                                                       December 17, 1984  
                                                       Page 2 of 2        

Cummins has discontinued the use of this flywheel and is currently using 
their standard truck engine flywheel (Part No. 2965) on the NT 855 F4 fire 
pump diesel. They have been running comparison tests on these two flywheels 
(Parts No. 2965 and No. 3453) and are considering recommending use of the 
truck engine flywheel as a replacement for the flywheel that has the 
cracking problem. The retrofit of the new flywheel (Part No. 2965) would 
require some modification because of size differences in the stub shafts. 

The following Cummins diesel fire pump engines that are equipped with 
flywheel Part No. 3453 are: 

     NH 220 IF 
     N 855 F 
     NT 855 F1 
     NT 855 F2 

No specific action or written response is required by this information 
notice. If you have any questions about this matter, please contact the 
Regional Administrator of the appropriate NRC regional office or this 
office. 


                                   Edward L. Jordan, Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contact:  Chauncey Gould 
                    (301) 492-8597 

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