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
                           WASHINGTON, D.C. 20555
                                July 1, 1983

                                   EQUIPMENT AS A RESULT OF BACKFLOW THROUGH
                                   THE EQUIPMENT AND FLOOR DRAIN SYSTEM 


All nuclear power reactor facilities holding an operating licensee (OL) or 
construction permit (CP). 


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. 


                                                               IN 83-44    
                                                               July 1, 1983 
                                                               Page 2 of 2 


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

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

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Page Last Reviewed/Updated Friday, May 22, 2015