United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 87-09: Emergency Diesel Generator Room Cooling Design Deficiency

                                                       SSINS No.: 6835 
                                                        IN 87-09

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

                              February 5, 1987


Information Notice No. 87-09:   EMERGENCY DIESEL GENERATOR ROOM COOLING 
                                   DESIGN DEFICIENCY 

Addressees: 

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

Purpose: 

This notice is to alert recipients of a potentially significant problem 
involving degradation of emergency diesel generators (EDGs) following and 
caused by a loss of offsite power (LOOP). It is expected that recipients 
will review this information for applicability to their facilities and 
consider actions, if appropriate, to preclude a similar problem occurring at 
their facilities. However, suggestions contained in this information notice 
do not constitute NRC equipments; therefore, no specific action or written 
response is required. 

Description of Circumstances: 

On December 24, 1986, the Carolina Power and Light Company determined that a 
reportable condition existed at the two Brunswick Steam Electric Plants in 
which a loss of offsite power could cause a common-mode loss of all four 
EDGs. Using probabilistic risk assessment methodology during a review of the 
EDGs in November 1986, the licensee discovered that the EDG room cooling air 
supply would isolate during a LOOP. 

At Brunswick, the outside air for EDG room cooling is drawn through two 
intakes with a duct from each intake plenum to each of the four EDG rooms. 
This air is for room ventilation only; the combustion air for the diesel 
engine is supplied separately. Each of the eight ducts has a pneumatically 
operated damper and two fusible link fire dampers. The fire dampers were 
retrofit items. The original air-operated damper was designed by United 
Engineers and Contractors Inc. to fail close upon loss of non-safety 
instrument air pressure. This air supply is provided by an air compressor 
that is powered by the non-safety balance of plant electrical supply and is 
not provided with standby ac or dc power. Should a LOOP occur, the 
non-safety instrument air pressure would decrease and allow the air-operated 
dampers to close. The temperature of the EDG room would increase, depending 
on the ambient temperature and heat from the diesel engine. The qualified 
EDG control panel temperature of 104 F could be exceeded, which might cause 
degradation and failure of the electrical and electronic components in the 
control panels. This in turn might disable the EDG when it is needed to 
mitigate the LOOP. 
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                                                           IN 87-09
                                                           February 5, 1987
                                                           Page 2 of 2


Discussion: 

The licensee has locked the air-operated damper open to permit EDG room 
cooling regardless of the non-safety instrument air status. After a review 
of the EDG room HVAC requirements is completed, the licensee will either 
remove the air-operated dampers or modify them to eliminate the potential 
for common mode failure resulting from interaction with a non-safety system.

The potential for this type of design problem may not be limited to the 
diesel room HVAC. Previous pneumatic problems have been discussed in IE 
Information Notices 86-50, "Inadequate Testing to Detect Failures of 
Safety-Related Pneumatic Components or Systems," June 18, 1986 and 86-51, 
"Excessive Pneumatic Leakage in the Automatic Depressurization System," June 
18, 1986. Some effects of loss of HVAC on electronics was discussed in IE 
Information Notice 85-89, "Potential Loss of Solid-State Instrumentation 
Following Failure of Control Room Cooling," November 19, 1985. 

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:  James C. Stewart, IE
                    (301) 492-9061

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