United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 84-69, Supplement 1: Operation of Emergency Diesel Generators

                                                     SSINS No.:            
                                                     IN 84-69, Supplement 1 

                               UNITED STATES 
                       NUCLEAR REGULATORY COMMISSION 
                    OFFICE OF INSPECTION AND ENFORCEMENT 
                            WASHINGTON, DC 20555 

                             February 24, 1986  

Information Notice No. 84-69, SUPPLEMENT 1:    OPERATION OF EMERGENCY 
                                                  DIESEL GENERATORS 

Addresses: 

All nuclear power reactor facilities holding an operating license (OL) or a 
construction permit (CP). 

Purpose: 

Information Notice 84-69, issued on August 29, 1984, was provided to alert 
recipients of potentially significant safety problems that can arise when 
one or more emergency diesel generators (EDGs) are operated in modes other 
than the prescribed standby service mode, such as loaded on non-emergency 
buses parallel with offsite power sources. The purpose of this supplement is 
to reemphasize the need for licensees to review the information provided in 
IN 84-69, in addition to the information contained herein, for applicability 
to their facilities and consider actions, if appropriate, to preclude 
similar problems at their facilities. However, suggestions contained in this
supplement do not constitute NRC requirements; therefore, no specific action
or written response is required. 

Description of Circumstances: 

Following a 10 CFR 50.72 report made to the NRC Headquarters Operations 
Center on August 12, 1985, it was discovered that Crystal River Unit 3 was 
continuously running the one operable EDG loaded in parallel with the grid 
while the other EDG was declared inoperable. Crystal River Technical 
Specifications require fast starting of the operable EDG (i.e., verifying 
that the diesel starts from ambient conditions and accelerates to the 
required speed within a required period of time) within 1 hour after the 
declaration of an inoperable EDG and every 8 hours thereafter. Because of a 
concern about increased EDG wear and reduced overall EDG reliability, the 
licensee chose to keep the EDG running loaded parallel to the offsite grid 
rather than fast starting the EDG every 8 hours. 

The licensee believed that continuous running was an acceptable alternative 
to the test starts required by the Technical Specifications and that the EDG
was operable per Technical Specifications while running in parallel with the
offsite power system. The licensee indicated also that it was aware of IN 
84-69 and had implemented procedures that prohibited operating the EDG 
parallel to the grid during inclement weather (e.g. , lightning, heavy 
winds). 
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                                                  IN 84-69, Supplement 1  
                                                  February 24, 1986       
                                                  Page 2 of 3             

Discussion: 

When an EDG is operated connected to offsite or nonvital loads, the 
emergency power system is not independent of disturbances on the nonvital 
and offsite power systems that can adversely affect emergency power 
availability. The situation is of particular concern when the onsite 
emergency power system is already in a degraded condition due to an EDG 
being inoperable and the operable EDG is loaded on non-emergency loads. In 
this condition, a disturbance in the non-emergency power system could result 
in both a loss of offsite power and a disabling of the remaining emergency 
power source. Although the events described in IN 84-69 occurred due to 
weather conditions, the concerns of the IN apply to parallel operation of 
EDGs with non-emergency loads at all times. 

If a fault develops while the EDG is connected to non-emergency buses, EDG 
availability for subsequent emergency demands may be affected. In some 
design configurations, the EDG would trip as a result of overcurrent or 
reverse power, actuate a lockout device, and require local operator action 
to reset the lockout. In such cases, the EDG is recoverable, but the 
timeliness of its availability is not comparable to that of having the EDG 
in its normal standby service. 

In other design configurations the EDG may not trip, but the operation of 
the load sequencer may be adversely affected. The load sequencer timers are 
often linked with the closing of the EDG output breaker or with detection of
loss of voltage on the bus. If the EDG does not trip, conditions are not 
proper for the designed operation of the load sequencers. Consequently, the 
EDG cannot perform automatically in a manner comparable to that of having 
the EDG in its normal standby mode. 

Another potential concern deals with the vulnerability of the EDG to trip 
signals which are bypassed for emergency demands but are operable for manual
starts and during running for test purposes. The EDG would be more 
vulnerable to such trips. 

The licensee's concern regarding excessive test starts is valid. In this 
particular case, the licensee was encouraged to address that concern more 
directly by submitting changes to the plant Technical Specifications. Such 
changes were approved for North Anna Unit 2 on April 25, 1985. 


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                                                    IN 84-69, Supplement 1 
                                                    February 24, 1986     
                                                    Page 3 of 3           

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 Contacts: Joseph G. Giitter, IE 
                    (301) 492-9001 

                    J. T. Beard, NRR 
                    (301) 492-7465 

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