Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
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
Attachment:
List of Recently Issue IE Information Notices
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