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Information Notice No. 83-44: Potential Damage to Redundant Safety Equipment as a Result of Backflow Through the Equipment and Floor Drain System
SSINS No.: 6835 IN 83-44 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 July 1, 1983 Information Notice No. 83-44: POTENTIAL DAMAGE TO REDUNDANT SAFETY EQUIPMENT AS A RESULT OF BACKFLOW THROUGH THE EQUIPMENT AND FLOOR DRAIN SYSTEM Addressees: All nuclear power reactor facilities holding an operating licensee (OL) or construction permit (CP). Purpose: This information notice is provided to amplify the information in IE Circular 78-06 (Potential Common Mode Flooding of ECCS Equipment Rooms of BWR Facilities) in response to a potentially related event at a PWR facility. IE Circular 78-06 applied specifically to ECCS equipment rooms and flooding of areas at lower elevations. This notice expands the concern to other safety-related compartments and damage as a result of backflow through equipment and floor drainage systems. It is expected that recipients will review this information notice for applicability to their facilities. Description of Circumstances: Baltimore Gas & Electric Co., the licensee for the Calvert Cliffs plant, received notification from Bechtel Corporation, the architect-engineer, that the watertight integrity of the service water pump rooms at both units could be impaired because check valves had not been installed in the floor drain system which drains by gravity to the turbine condenser pit in the turbine building. The service water system at Calvert Cliffs serves both safety (the containment cooling units and the emergency diesel generator heat exchangers) and nonsafety equipment. Each unit has a room in the auxiliary building where its three service water pumps are located. The systems can be cross connected, by spool pieces, to allow one unit's system to back up the other unit. However, both units share a common turbine building so that both of the service water pump rooms would be simultaneously affected by flooding of the turbine building if backflow protection was not provided. The licensee has sealed some of the room drains and modified the remaining drain lines by installing check valves to prevent potential backflow into the safety-related rooms. 8305110502 . IN 83-44 July 1, 1983 Page 2 of 2 Discussion: At the Calvert Cliffs plant, the relative elevations of the turbine building and the service water pump room are such that, without backflow protection in the floor drains of the service water pump room, a circulating water conduit break in the turbine building or a design-basis flood could flood the turbine condenser pit and result in 15 feet of water in both service water pump rooms (see Figure 1). Although instrumentation would detect and annunciate an increase in water level in the turbine pit and the service water pump rooms, there would be no way to stop the flow of water in the event of a design-basis flood. A loss of service water flow would affect the four containment air coolers for each unit and all three emergency diesel generators at the site. If containment cooling via the air coolers is lost, containment heat removal and pressure control following a LOCA, can be accomplished with the containment spray system. The containment spray is pumped through the shutdown cooling heat exchanger and transfers heat to the component cooling water system. The latter system is not affected by the postulated flooding. However, if the service water pump rooms flooded at the same time as there was a loss of offsite power, both units would experience a total loss of AC power, since cooling for all the emergency diesels at the site would also be lost. A recently completed engineering evaluation by the NRC Office for Analysis and Evaluation of Operational Data concluded that the subject of potential damage to redundant safety equipment as a result of backflow through the equipment and floor drain system has not been addressed for some older plants [i.e. plants not fully reviewed in accordance with the Standard Review Plan (SRP) and thus not necessarily designed to the standards of SRP section 9.3.3 that provides guidance for equipment and floor drainage systems]. Therefore, these plants may be susceptible to the same or equivalent potential problem identified at the Calvert Cliffs plant. Because of differing designs these plants could have equivalent problems, but involving different components or systems of components. No written response to this information notice is required. If you have any questions about this matter, please contact the Regional Administrator of the appropriate NRC Regional Office, or this office. Edward L. Jordan Director Division of Emergency Preparedness and Engineering Response Office of Inspection and Enforcement Technical Contact: C. Campbell, IE 301-492-9762 Attachments: 1. Figure 1 2. List of Recently Issued IE Information Notices .
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