Effects of Accelerator-Driven Transmutation System on Radiotoxicity of High-Level Radioactive Wastes

We have developed a computation tool, WAste COMposition (WACOM) for performing a scoping study of the effects of the accelerator-driven transmutation of waste (ATW) system with a lead-bismuth-eutectic-cooled transmuter on actinide inventory and radiotoxicity reduction. WACOM consists of a simplified burnup model for a chain of 18 actinide isotopes and a fuel cycle model to evaluate high-level waste (HLW) generation from the reference ATW plant. Interpolation formulas for effective one-group cross sections as a function of the actinide mass fraction have been developed. Three kinds of HLW generation were considered: (a) HLW from uranium separation for light water reactor (LWR) spent fuel, (b) HLW from the partitioning process in multicycle ATW operation, and (c) the last core of the transmuter at the decommissioning of the ATW system. The latter two HLW sources resulting from multicycle ATW operation have been found to be greater than the first source. Potential benefits of ATW deployment have been found to be (a) reduction of the total actinide toxicity by a factor of 48 at the time of waste generation and (b) conversion of the actinide mixture into a more proliferation-resistant configuration, by effective transmutation of ²³⁹Pu, ²⁴¹Am, and ²³⁷Np included in the LWR spent fuel. The total actinide radiotoxicity further decreases to 1/260 for the time period of 100 000 yr, which would improve the performance of the Yucca Mountain Repository.