Fuel optimization and transient analysis of a medium temperature heat pipe reactor

Micro reactors, particularly Heat Pipe cooled Reactors (HPRs), have been recognized as leading candidates for decentralized electricity markets due to their inherent safety, compact size, and transportability. However, conventional HPRs are operated at high temperatures, posing challenges related to material corrosion, thermal stresses, and startup failures. To address these issues, Medium Temperature Heat Pipe cooled Reactors (MTRs) operating at 350 °C have been proposed. In this work, three representative fuels are systematically evaluated: uranium-zirconium hydride (U-ZrH_1.6), uranium dioxide (UO₂), and uranium-silicide composite (U₃Si₂-Al). All three fuels are indicated by steady-state calculations to be suitable for normal operation of MTR. Transient simulations are conducted to assess the behavior of fuels under single and multiple heat pipe failure situations. Results are shown to indicate that while the centerline temperatures of all fuels remain below their respective melting points, the maximum temperature of U₃Si₂-Al fuel is found to exceed the recommended safety threshold. Although the U-ZrH_1.6 fuel is considered to exhibit slightly better neutron economic performance than UO₂, its safety margin is determined to be significantly lower than that of UO₂. In conclusion, UO₂ is identified as the preferred fuel candidate for MTR.