Different fuel and fuel cycle concepts have been considered in the reactor, arranged in a sub-critical state. Some of the primary areas of research at various laboratories are shown in Table 13.2. These are expanded further in Section 13.8.

Brookhaven National Laboratory (BNL) has focused mainly on fast spectrum concepts, liquid sodium cooling and oxide or metal solid fuels based on sodium-cooled fast reactor technology. Also in that laboratory, particle bed/bead fuel has been investigated in the thermal spectrum, as considered in space propulsion reactor technology.

In Japan, the Japanese Atomic Energy Research Institute (JAERI) has concentrated on MA burning in a fast neutron spectrum, with solid fuel also based on sodium-cooled fast reactor technology, or molten chloride fuel, as yet an unproven technology.

Los Alamos National Laboratory (LANL) has developed a concept based on a thermal neutron spectrum with molten fluoride fuels with different fissile materials such as weapons grade plutonium, LWR spent fuel (minor actinide and fission products) and thorium fuels based on molten salt water reactor technology. Liquid lead-bismuth systems in the fast spectrum have also been considered.

The CERN group in Geneva, Switzerland, has put forward the concept of solid ThO2/233UO2 fuel in a fast spectrum based on liquid lead/liquid lead-bismuth reactor technology. This uses a cyclotron-based system. The applications are for energy production or waste transmutation.

At the Institute of Theoretical and Experimental Physics (ITEP) in Russia, different technologies for the conversion of weapons plutonium and long-lived radioactive waste are being considered. These include heavy water suspensions, molten fluoride and liquid lead fast spectrum systems.

Work is also being carried out in various laboratories within the EU, including France, Germany, Italy, Sweden and the UK. Within France for example, research, carried out at CEA has focused on options for radioactive waste management.

There are clearly many options under investigation in the international community, which offer a reprocessing capability for nuclear fuel and in the case of weapons plutonium, a means for the reduction in the world’s stockpile of plutonium. Further assessment of the various options is continuing.