United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-73: Recent Emergency Diesel Generator Problems

                                                            SSINS No.: 6835 
                                                                   IN 86-73 

                                UNITED STATES
                           WASHINGTON, D.C. 20555

                               August 20, 1986

Information Notice No. 86-73:   RECENT EMERGENCY DIESEL GENERATOR 


All nuclear power reactor facilities holding an operating license or a 
construction permit. 


This notice is to alert addressees to vibration-induced fuel line wear and 
of a deficiency in the design of the field flash circuitry on nuclear plant 
emergency diesel generators. Recipients are expected to 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 

Description of Circumstances: 

Nine Mile Point Unit 2 

While conducting diesel generator testing in early May 1986, it was 
discovered that diesel fuel lines had experienced extensive wear and fuel 
leaks in the area of the clamps that mount the fuel lines to the diesel 
engine. The diesels are Cooper-Bessemer model KSV-16-T, 600 rpm, 4 stroke, 
16 cylinder units with low total operating hours. 

Fuel line damage was caused by vibration from the diesel engine and fuel 
system pulsation induced by rapid, repeated cycling of a fuel system relief 
valve. This valve relieves from the low pressure fuel system via a cooler to
the fuel day tank to control low pressure fuel system pressure. The 
manufacturer proposes to correct the problem by inserting plastic sleeves 
between the fuel line and, its hold down clamps and installing a dashpot on 
the relief valve to dampen its operation. 

Watts Bar Units 1 and 2 

In April 1986 a deficiency was identified which affects all five standby 
diesel generators (DGs) at Watts Bar Nuclear Plant and could prevent the DGs
from developing a voltage output when required in an emergency. The affected
DGs are tandem 16-645 E4 units supplied by Morrison-Knudson Co. The normal 
shutdown cycle of the DG includes a 10-minute cooldown run at about 450 rpm.
If during 


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                                                           August 20, 1986 
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this idle period an emergency signal were received, the DG would accelerate 
to the normal 900 rpm operating speed, but the generator field would not be 
flashed and an output voltage therefore would not be developed. 

This problem has also been determined to exist on the HPCS DG at Grand Gulf 
Nuclear Station. This unit was supplied by General Motors Corporation. 

The root cause of this deficiency has been found to be a design error by the
manufacturer. During a normal or emergency start, as the DG accelerates past
475 rpm, logic is completed to flash the generator field. When output 
voltage has built up, the field flash circuitry is automatically disabled. 
The logic design is such that engine speed must go below 200 rpm to 
re-enable the field flash circuitry, thus no field flash will occur if an 
emergency start signal is received during the 450 rpm cooldown period. Field 
flash would be needed under these circumstances because the self-excitation 
path is interrupted early in the shutdown sequence. 

The corrective action proposed by the DG manufacturer is to modify the 
control circuitry to eliminate the speed dependence of field flash reset. 

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 regional office or this office. 

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

Technical Contact:  Kevin Wolley, IE
                    (301) 492-8373

Attachments: List of Recently Issued IE Information Notices
Page Last Reviewed/Updated Friday, May 22, 2015