Research and development activities for accelerator-driven system in JAEA

The Japan Atomic Energy Agency (JAEA) has investigated an accelerator-driven system (ADS) to transmute minor actinides which will be partitioned from the high level waste. There are various inherent issues for the research and development on the ADS. The recent two activities to realize a feasible and reliable ADS concept are introduced in this paper. For the feasibility, the design of a beam window which is a boundary of the accelerator and the subcritical core, is one of the most important issues. To mitigate the design condition of the beam window, namely to reduce the necessary proton beam current, the subcritical core concept with subcriticality adjustment rods was investigated. Through the coupled analysis of neutronics, particle transport, thermal-hydraulics and structure, a feasible beam window concept was presented. For the reliability, a beam-trip is the inherent and serious issue for the ADS design because it induces a rapid temperature change in structures in the subcritical core. In the previous study, the beam-trip frequency of the ADS accelerator was estimated based on the operation data of the existing accelerators. To minimize the beam trip frequencies, a double-accelerator concept was proposed and its beam-trip frequency was estimated. The results indicated that the double-accelerator concept was useful to realize reliable accelerator operation for the ADS although the cost of the accelerators and those buildings would be double.