Nuclear Transmutation of ⁹⁹Tc Utilizing Proton Spallation and Compact Subcritical Assembly

An innovative design is introduced for neutron transmutation employing a proton accelerator in conjunction with a compact subcritical system. The transmutation converter comprises a spherical target enveloped by a subcritical assembly. The subcritical assembly consists of a moderator and low-enriched uranium in shell plates. The subcritical assembly has an inner radius of 10 cm and a thickness of 40 or 55 cm. The material used for the target is lead, and beryllium or beryllium oxide is used as a moderator. Low-enriched uranium in the subcritical assembly contains 5% ²³⁵U. The transmutation half-life is inversely proportional to the integral of epithermal ⁹⁹Tc capture rates. The MCNP6 simulation demonstrates that the transmutation half-life is less than 1 year when exposed to 1-GeV protons at 5 mA. Additionally, it is notable that this half-life can be further reduced with increased proton energies and currents. Previous studies have reported that the ⁹⁹Tc transmutation half-life using fast reactors and an accelerator-driven system ranges from tens to hundred years; this design concept represents a substantial advancement to previous research efforts.