Part 21 Report - 1995-039


Licensee/Facility:                     Notification:

Niagara Mohawk Power Corp.             MR Number: 1-95-0015
Nine Mile Point 2                      Date: 02/01/95
Lycoming,New York                      SRI PC                             
Dockets: 50-410

Reportable Event Number: 28304                         


On January 29, 1995, NMPC commenced a shutdown of Unit 2, and declared an
Unusual Event as a result of both Emergency Diesel Generators (EDG) being
On January 26, 1995, during routine monthly surveillance testing, the    
Division I EDG exhibited instability in the engine control system and    
tripped when its output circuit breaker was tripped. Troubleshooting of  
the control system indicated a problem with the electric governor or the 
DC governor power supply (the engines are equipped with both electric and
mechanical governors). The applicable Technical Specification (TS)       
limiting condition for operation (LCO) was entered, and the Division II  
EDG was tested. No instability was noted during the run of the Div II    
After replacing the Div I EDG electric governor control card, the Div I  
EDG was tested, and still exhibited instability. During subsequent       
troubleshooting, excessive temperatures were noted at the base of the    
governor, and it was determined that the mechanical governor was         
malfunctioning. The mechanical governor was replaced and on retest, the  
engine was noted to operate properly, but the governor was still         
experiencing excessive temperatures. The Div II EDG was run to obtain    
temperature profiles on its governor, and it was determined that its     
governor was also experiencing excessive temperatures. At the end of the 
test run, the Div II EDG failed to trip due to an air leak on the        
pneumatic controls. The Div II EDG was declared inoperable and a reactor 
shutdown was commenced (the Div II EDG was INOP, but available).         
NMPC has determined that the governor coolers were receiving inadequate  
flow from the jacket cooling water system, and has instituted a design   
change to rectify the problem. NMPC has also determined that the         
manufacturer (Cooper-Bessemer) has used several different jacket cooling 
water system designs, and notified the two facilities with similar       
systems (Byron and Braidwood) of the problem.                            
The governor on the Div II EDG has been replaced due to having been      
subjected to excessive temperatures. The problem is believed to be       
long-term degradation of the governor oil and mechanical components due  
to the high temperatures. The governors from both engines will be sent   
out for failure analysis.                                                
As of 8:00 a.m. February 1, the modifications on both engines have been  
completed, and testing of the Div II EDG is in progress (Div I EDG       

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