FIG. 24 illustrates a region 2434 within the shell of the heat exchanger that is above the level of fuel salt in the reactor core 2404. This region may be filled, except for the penetrating tubes, with any reflecting or moderating material, for example filled with a different or the same reflector material as the reflector/coolant.
In FIG. 24, the upper reflector 2408A and lower reflector 2408B are illustrated as distinct from the circulating reflector/coolant material. In an alternative embodiment, the upper reflector 2408A, lower reflector 2408B, and inner reflector 2408C may all be in fluid communication as shown in FIGS. 22 and 23. For example, reflector material may be routed into reactor 2400 along the interior surface of the side of the containment vessel 2418, as shown, but then routed along the bottom of the containment vessel 2418 before rising and making a U-turn to flow adjacent to the bottom of the reactor core 2404, as shown in FIG. 23. The reflector material may also be routed into the upper reflector 2308A from which it can be removed at a central location, also as shown in FIG. 23.
A pump (not shown), or at least the impeller of a pump, may be provided to assist in fuel salt circulation or reflector/coolant circulation. For example, an impeller may be provided in one or both of the heated fuel salt inlet to the primary heat exchanger at the top of the reactor core 2404 or (as discussed in greater detail below) the cooled fuel outlet of the shell of the primary heat exchanger at the bottom of the reactor core 2404.
