Reflector drums as control mechanism for compact thermionic spacecraft reactors with 233U as fuel

The extreme compactness of thermionic reactors with 233U as nuclear fuel for space craft application permits the use of boronated reflector drums as a control mechanism. This leads to the reduction of the radiation shield diameter compared with that needed for control through moveable reflector segments. A ZrHsub(1.7) moderated reactor with a constant ratio of moderator to fuel, and a beryllium-moderated reactor with variable ratio of moderator to fuel, but with a spatially quasi-constant emitter heating are studied. (author)