An IHX Design for Pool Type LMFBR System Application

This paper presents the design of a 500 MWt Intermediate Heat Exchanger (IHX) for application in a multi-zone pool-type Liquid Metal Fast Breeder Reactor System. The primary feature around which this design was developed is the ability to function under all steady-state and transient conditions without the need for a distinct mechanical feature to accommodate differential thermal expansion between the tube bundle and shell. This is accomplished by using thermal baffles and judiciously adjusting the ratio of shell length in contact with the hot and cold pools of the multi-zone reactor. Thus, the component shell is maintained at a higher temperature than the tube bundle and the tubes are basically tension members. Under certain transient conditions the tubes heat up and become compression members but are not loaded to the point of buckling. A secondary, but not less significant, feature is the low primary side pressure drop and good flow distribution offered by this design. (Multi-zone reactor systems have no hard piping between the IHX outlet and primary pump inlet; therefore, the relatively small differential head of sodium between the two pools is the only driving element which causes flow through the primary side of the IHX. For this reason, a low primary side pressure drop is essential). To accomplish this, the primary sodium flows through the tube side of the component where the flow channel is simple and unimpeded by tube supports or other restrictions. Secondary flow distribution, through the shell side of the unit, can be adjusted as required since a higher pressure drop can be tolerated.