heterogeneous reactor[‚hed·ə·rə′jē·nē·əs rē′ak·tər]
a nuclear reactor that is constructed to isolate the fuel from the other elements and materials of the core.
The presence of heat-releasing elements, such as fuel assemblies and fuel channels, is an indication of the heterogeneous nature of a reactor. The heat-releasing elements can be of the most diverse shapes in construction (plates, for example, or rods of round, cruciform, or annular cross section), but in every case there is a sharp boundary in the heterogeneous reactor between the nuclear fuel, the moderator, and the coolant.
In practice, the vast majority of nuclear reactors of all possible types and purposes are heterogeneous. This broad distribution of heterogeneous reactors is due to their vastly greater constructional and technological advantages in comparison to homogeneous reactors.
IU. I. KORIAKIN