Cross-sectional comparison of the core configurations of the pilot-scale ADS (thermal output in Phases 1–3: 200 MW) and the commercial ADS (thermal output: 800 MW). The core configuration of the pilot-scale ADS is changed in stages from a MOX^*2 fuel core to a nitride fuel core containing minor actinides (MAs), with additional safety rods installed to maintain a large subcritical margin.

Transmuting minor actinides (MAs) contained in high-level radioactive waste is an effective way to reduce the waste’s long-term heat generation and radioactivity, thereby contributing to reductions in waste volume and radiotoxicity. The Japan Atomic Energy Agency has designed a commercial accelerator-driven system (ADS)^*1 with a thermal output of 800 MW, capable of transmuting approximately 250 kg of MAs per year. Realizing a commercial ADS requires the stepwise demonstration of fuel, accelerator, and beam-window materials technologies.

In this study, we proposed a pilot-scale ADS with a thermal output of 200 MW—one-quarter of that of the commercial ADS—and developed conceptual designs for its core, accelerator, lead-bismuth target, and reactor components for the demonstration of these technologies. The pilot-scale ADS initially uses MOX^*2 fuel without MAs, drawing on experience with MOX fuel in existing nuclear systems. From Phase 1 to Phase 2, the core power density is increased to verify basic core performance. The core is then transitioned to MA-bearing nitride fuel in Phase 3 (Fig. 1). The pilot-scale ADS also incorporates safety rods, which are not included in the commercial ADS design, thereby enabling operation with a large subcritical margin. The accelerator is designed as a superconducting linac delivering a 1.0 GeV, 10 mA proton beam, with a more compact configuration and lower beam power than the accelerator for the commercial ADS. Realizing this accelerator requires further development of high-current operation and fault tolerance, which allows operation to continue despite equipment failures. These technologies are to be demonstrated in stages, starting with the low-energy section. We applied most of the international safety design criteria for lead-cooled fast reactors to this conceptual design and developed specifications for the core, accelerator, lead-bismuth target, and reactor vessel.

This study establishes a pathway toward realizing commercial ADSs through the stepwise demonstration of technologies across Phases 1–3, contributing to a sustainable society through the practical application of partitioning and transmutation technologies.

 

^*1 ADS: A system that generates a large number of neutrons by directing an accelerator-produced proton beam onto a target material and then multiplies the generated neutrons in a subcritical core.

^*2 MOX: Mixed oxide fuel made from uranium and plutonium, with a proven track record in light-water reactors and other nuclear systems.

Paper URL: https://doi.org/10.15669/pnst.8.185

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