Neutronics analysis of a subcritical blanket system driven by a gas dynamic trap-based fusion neutron source for 99 Mo production

Gamma-emitting radionuclide 99m Tc is globally used for the diagnosis of various pathological conditions owing to its ideal single-photon emission computed tomography (SPECT) characteristics. However, the short half-life of 99m Tc ( T 1/2 = 6 h) makes it difficult to store or transport. Thus, the production of 99m Tc is tied to its parent radionuclide 99 Mo ( T 1/2 = 66 h). The major production paths are based on accelerators and research reactors. The reactor process presents the potential for nuclear proliferation owing to its use of highly enriched uranium (HEU). Accelerator-based methods tend to use deuterium–tritium (D–T) neutron sources but are hindered by the high cost of tritium and its challenging operation. In this study, a new 99 Mo production design was developed based on a deuterium–deuterium (D–D) gas dynamic trap fusion neutron source (GDT-FNS) and a subcritical blanket system (SBS) assembly with a low-enriched uranium (LEU) solution. GDT-FNS can provide a relatively high-neutron intensity, which is one of the advantages of 99 Mo production. We provide a Monte Carlo-based neutronics analysis covering the calculation of the subcritical multiplication factor ( k s ) of the SBS, optimization design for the reflector, shielding layer, and 99 Mo production capacity. Other calculations, including the neutron flux and nuclear heating distributions, are also provided for an overall evaluation of the production system. The results demonstrated that the SBS meets the nuclear critical safety design requirement ( k s < 0.97) and maintained a high 99 Mo production capacity. The proposed system can generate approximately 157 Ci 99 Mo for a stable 24 h operation with a neutron intensity of 1 × 10 14 n/s, which can meet 50% of China’s demand in 2025.