TOPAZ-II
In the TOPAZ-II or ENISY reactor each fuel pin (96% enriched UO2) is sheathed in an emitter which is in turn surrounded by a collector, and these form the 37 fuel elements which penetrate the cylindrical zirconium hydride (ZrH) moderator. This in turn is surrounded by a beryllium neutron reflector with 12 rotating control drums. Liquid metal coolant (NaK) surrounds each fuel element. The mass of the reactor is ~ 1,061 kg (2,340 lb).
In January 1991 a model of the TOPAZ-II was exhibited at a scientific symposium in Albuquerque, generating interest in the US in the possible purchase of it and the Strategic Defense Initiative Organization arranged to buy two Topaz-2 reactors from Russia for a total of $13 million, planning to use the reactors to improve US models. However, the Nuclear Regulatory Commission ruled that US law prohibited the "export" of such a device to the Soviet Union - even though it was Soviet-made and only a model rather than an actual reactor. It took a month before the situation was resolved by a new NRC ruling and the model returned to Russia.
The United States Department of State then put a hold on the deal, which was only lifted when Secretary of State James Baker intervened. One of the reactors was to be used in a flight test in 1995 to power experimental electrical thrusters, but there were objections from scientists concerned about the possible impact of radiation emitted by the reactor on instruments aboard space satellites and protests from opponents of space-based weapons and nuclear power. In addition, the Department of Energy was slow to grant the necessary approval and in 1993 budget restrictions forced the cancellation of the program.
Six TOPAZ-II reactors and their associated support equipment were flown to the US, where they were extensively ground tested by US, British, French, and Russian engineers. The reactors' unique design allowed them to be tested without being fuelled. Although the test program was considered a success, no plans were pursued to fly any of the reactors.
Read more about this topic: TOPAZ Nuclear Reactor