Neutronics analysis of LANL's accelerator transmutation of waste

The Los Alamos National Laboratory's (LANL's) accelerator transmutation concept is directed at the problems associated with high-level wastes stored at several US Department of Energy sites. A high-energy (1,600-MeV), high-current (25- to 60-mA) proton accelerator is used as a driver. The protons are directed onto a flowing liquid lead-bismuth (Pb-Bi) target and through the process of spallation generates ∼50 neutrons for each incident proton. The neutrons are moderated to thermal energy in a surrounding blanket of heavy water (D2O) and are used to transmute fission products, capture and fission actinides, or directly fission fissile isotopes. Because of the intense flux of neutrons generated, very dilute mixtures are used, thereby reducing the potential for criticality and power excursion. In this proposed design, the authors have devised a system to transmute high-level defense fission product and actinide waste at Hanford. Specifically, the system is designed for transmutation of the long-lived fission products 99Tc and 129I, and the higher actinides 237Np and 241,243Am. For the total inventory at Hanford of 2,000 kg of technetium and iodine and 400 kg of neptunium and americium, the goal transmutation rates for a 30-yr operation are 67 kg/yr for the fission products and 13 kg/yr for actinides. It is concluded that the LANL accelerator transmutation concept is feasible and can transmute the long-lived defense waste at a site like Hanford