Information Notice No. 92-69: Water Leakage from Yard Area Through Conduits Into Buildings

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                            WASHINGTON, D.C.  20555

                              September 22, 1992

                               CONDUITS INTO BUILDINGS


All holders of operating licenses or construction permits for nuclear power


The U.S. Nuclear Regulatory Commission is issuing this information notice to
alert addressees to problems resulting from large amounts of water leaking
into the reactor building through electrical conduits.  It is expected that
recipients will review the information for applicability to their facilities
and consider actions, as appropriate, to avoid similar problems.  However,
suggestions contained in this information notice are not NRC requirements;
therefore, no specific action or written response is required.

Description of Circumstances

On November 19, 1991, following a thunderstorm, the licensee for the Grand
Gulf Nuclear Station observed a significant amount of rain water entering the
auxiliary building through electrical conduits.  Most of the leakage was from
around one condulet cover plate; a number of other condulet cover plates were
dripping water.  The conduits originated in a large manhole located in the
adjacent yard area through which the licensee had routed many electric cables
by way of an underground conduit.  The licensee found that the sump pump in
this manhole was not operating, probably because of heavy rainfall on the
circuit box, which tripped the circuit breaker for the pump.  Water then
collected in the manhole and flowed through the conduits which were routed
into the auxiliary building.  These conduits were to have internal seals near
the wall of the auxiliary building and upstream of the leaking condulet cover
plates.  The licensee found that some seals were below or downstream of the
condulet cover plates.  Water that leaked from the conduits collected on the
floor, ran through a doorway into the division I switchgear room, and passed
through floor drains to the radwaste collection tank.  About 30,000 gallons of
water collected in these tanks.  Water marks indicated the maximum water level
on the floor was about 1 inch.  No safety systems were affected.

On December 22, 1991, a 36-inch fiberglass auxiliary circulating water line 
failed at the Perry Nuclear Power Plant.  The failure was in a non-isolable
section located in a yard area above grade just before the line enters the
heater bay building.  An estimated 2.9 million gallons of water was pumped out
of the break.  A small percentage of this amount entered the auxiliary 


                                                            IN 92-69
                                                            September 22, 1992
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building, the heater bay, the service water pump house, and the emergency
service water (ESW) pump house.  Two electrical manholes had previously leaked
during rains and were not designed to be leak tight against standing water.  
Conduits in these manholes formed a direct path into the buildings where the
cables enter.  In particular, water entered the ESW pump house through a
series of conduits and ran down a cable into a compartment of a motor control
center (MCC), causing a short circuit in a space heater transformer.  This MCC
also contained safety-related equipment, which was not damaged.  


In both instances, large quantities of water entered buildings and areas
within the buildings that contain safety-related equipment.  The leak path
through yard manholes and connecting electrical conduits was not explicitly
considered in the safety analysis.  At Grand Gulf, although seals installed in
manholes and conduits were not required to be leak tight against water intru-
sion, the licensee found them to be deficient with respect to a design
drawing.  These conduits were sealed.  The licensee for Perry also sealed the
conduits.  The licensees did not inspect seals or perform tests that would
detect the absence or deterioration of installed seals.

This information notice requires no specific action or written response.  If
you have any questions about the information in this notice, please contact
the technical contact listed below or the appropriate Office of Nuclear
Reactor Regulation (NRR) project manager.

                                       ORIGINAL SIGNED BY

                                   Charles E. Rossi, Director
                                   Division of Operational Events Assessment
                                   Office of Nuclear Reactor Regulation

Technical contact:  J. Carter, NRR
                    (301) 504-1153

Attachment:  List of Recently Issued NRC Information Notices 


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