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Information Notice No. 92-69: Water Leakage from Yard Area Through Conduits Into Buildings
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 September 22, 1992 NRC INFORMATION NOTICE 92-69: WATER LEAKAGE FROM YARD AREA THROUGH CONDUITS INTO BUILDINGS Addressees All holders of operating licenses or construction permits for nuclear power reactors. Purpose 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 9209160134. IN 92-69 September 22, 1992 Page 2 of 2 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. Discussion 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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