IE Circular No. 78-06, Potential Common Mode Flooding of ECCS Equipment Rooms at BWR Facilities
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 IE Circular No. 78-06 Date: May 31, 1978 Page 1 of 2 POTENTIAL COMMON MODE FLOODING OF ECCS EQUIPMENT ROOMS AT BWR FACILITIES Georgia Power Company (GPC), by letter dated March 22, 1978, reported that during a review of the design of the ECCS corner room equipment drain systems at the Hatch facilities, the equipment drain lines for Hatch 1 were found piped into the top of an open 6-inch pipe (standpipe) in each corner room. These corner room standpipes are interconnected by a 6-inch pipe to a common sump in one corner room. This sump has redundant pumps which are powered from different emergency buses. The equipment drain system does not have any isolation valves within any of the piping between corner rooms. Therefore, in the event of a pipe break of sufficient size to flood sump pumps, the other ECCS corner rooms would be subject to flooding via the equipment drain piping. Since one of the reasons for installing the ECCS equipment in separate, watertight rooms was to eliminate the potential for common flooding, GPC is "hard piping" all of the equipment drain lines into the side of the corner room standpipe and capping the standpipe. This limits the size of the potential flooding backflow to the small size (approximately 1/2") piping of the equipment leakoff drain line. The above described design for Hatch 1 and 2 was part of the A-E balance- of-plant design provided by Bechtel. All holders of reactor operating licenses should assure that similar pathways, which could lead to common flooding of redundant equipment, do not exist in their facilities. It is recommended that the following items be considered in your review of this matter: 1. The specific design and installation for floor and equipment drains should be reviewed to verify that a flood in any one room or location would not result in flooding redundant equipment in other ECCS equipment rooms or in areas at a lower elevation. . IE Circular No. 78-06 Date: May 31, 1978 Page 2 of 2 2. If your installation depends on isolation valves and limit switches to prevent common flooding, your surveillance program should be reviewed to verify adequate maintenance of protection. Your Technical Specifications should be reviewed to assure that necessary surveillance of isolation valves, level switches, or sump pumps are included as appropriate. 3. Your administrative controls should also be reviewed to assure that separation criteria is maintained and watertight doors and/or hatches are closed as appropriate. This Circular is also issued to holders of construction permits for information or use as appropriate to the status of plant construction. No written response to this Circular is required. If you require additional information regarding this matter, contact the Director of the appropriate NRC Regional Office.
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