IE Information No. 87-09: Emergency diesel generator room cooling design deficiency

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 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