LANL has been studying accelerator driven transmutation technology (ADTT) for the destruction of nuclear waste and for generating power by systems which do not generate hazardous waste, and destroy their own waste. One particular approach called the accelerator driven energy production (ADEP) process, generates nuclear energy from thorium, avoids the production of plutonium and destroys its long-lived high-level fission product waste (Bowman, 1997).

The system is based on 232Th, which is converted by neutron absorption to the fissile component 233U from which the energy is generated. The system contains a target/blanket that contains the fissile material and the waste to be destroyed. A continuous chain of fissions is produced, by an external neutron source that allows for the expenditure of neutrons on waste destruction (there are about 5-10% fewer neutrons than would otherwise be necessary to maintain a chain reaction). Thus without this external source, the system would not be self-sustaining.

In the ADTT, an 800 MeV proton beam is directed onto a lead target in an assembly containing the target and a surrounding blanket including the fissile material. The blanket acts as a moderator and consists mostly of graphite and molten salt containing the fissile fuel as an actinide fluoride. The graphite and molten salt are compatible; this has been established from long-term experience with the molten salt reactor at ORNL (Weinberg, 1970). The system multiplies the neutrons produced by the beam by about a factor of 20 operating at a keff of 0.95. Heat is removed from the blanket by internal heat exchangers, which transfer heat from the primary working salt to a secondary external salt stream, thence to a steam generator for electric power production. The majority of power generated goes to the grid; about 10-15% is used to power the accelerator. The liquid fuel system is continuously fuelled. It is regularly cleaned to enable fission products to be continuously removed.

The accelerator transmutation of waste (ATW) project is part of the ADTT programme. It has the specific objective to destroy the actinide and long-life fission products from waste arising from the commercial nuclear programme. ATWs are considered in the molten salt thermal spectrum, see Figure 13.3, and liquid lead-bismuth in the fast spectrum.