Los Alamos National Laboratory has led the development of accelerator-driven transmutation of waste (ATW) to provide an alternative technological solution to the disposition of nuclear waste. While ATW will not eliminate the need for a high-level waste repository, it offers a new technology option for altering the nature of nuclear waste and enhancing the capability of a repository. The basic concept of ATW focuses on reducing the time horizon for the radiological risk from hundreds of thousands of years to a few hundred years and on reducing the thermal loading. As such, ATW will greatly reduce the amount of transuranic elements that will be disposed of in a high-level waste repository. The goal of the ATW nuclear subsystem is to produce three orders of magnitude reduction in the long-term radiotoxicity of the waste sent to a repository, including losses through processing. If the goal is met, the radiotoxicity of ATW-treated waste after 300 yr would be less than that of untreated waste after 100 000 yr.

These objectives can be achieved through the use of high neutron fluxes produced in accelerator-driven subcritical systems. While critical fission reactors can produce high neutron fluxes to destroy actinides and select fission products, the effectiveness of the destruction is limited by the criticality requirement. Furthermore, a substantial amount of excess reactivity would have to be supplied initially and compensated for by control poisons. To overcome these intrinsic limitations, we searched for solutions in subcritical systems freed from the criticality requirement by taking advantage of the recent breakthroughs in accelerator technology and the release of liquid lead/bismuth nuclear coolant technology from Russia. The effort led to the selection of an accelerator-driven subcritical system that results in the destruction of the actinides and fission products of concern as well as permitting easy operational control through the external control of the neutron source.