Disposition of nuclear waste using subcritical accelerator-driven systems:Technology choices and implementation scenarios

Los Alamos National Laboratory has led the development of accelerator-drive n transmutation of waste (ATW) to provide an alternative technological solu tion 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 f or altering the nature of nuclear waste and enhancing the capability of a r epository. The basic concept of ATW focuses on reducing the time horizon fo r the radiological risk from hundreds of thousands of years to a few hundre d years and on reducing the thermal loading. As such, ATW will greatly redu ce the amount of transuranic elements that will be disposed of in a high-le vel waste repository The goal of the ATW nuclear subsystem is to produce th ree orders of magnitude reduction in the long-term radiotoxicity of the was te sent to a repository, including losses through processing. If the goal i s met, the radiotoxicity of ATW treated waste after 300 yr would be less th an that of untreated waste after 100 000 yr. These objectives can be achieved through the use of high neutron fluxes pro duced in accelerator-driven subcritical systems. While critical fission rea ctors can produce high neutron fluxes to destroy actinides and select fissi on products, the effectiveness of the destruction is limited by the critica lity requirement Furthermore, a substantial amount of excess reactivity wou ld have to be supplied initially and compensated for by control poisons. To overcome these intrinsic limitations, we searched for solutions in subcrit ical systems freed from the criticality requirement by taking advantage of the recent breakthroughs in accelerator technology and the release of liqui d lead/bismuth nuclear coolant technology from Russia. The effort led to th e selection of an accelerator-driven subcritical system that results in the destruction of the actinides and fission products of concern as well as pe rmitting easy operational control through the external control of the neutr on source.