Hydride fuel irradiation in MITR-II: Thermal design and validation results

Abstract

Hydride metallic fuel is known to have several advantages compared to uranium oxide fuel, including enhanced thermal conductivity, large negative temperature reactivity coefficient, and reduced requirement for water moderator. In order to investigate the fuel performances under the irradiation condition, the hydride fuel irradiation (HYFI) experiment was designed and tested in the MIT Research Reactor-II (MITR-II) core. The HYFI facility consists of three fuel rod capsules with cover gas system, and instrumentation and data acquisition system. Each fuel rod capsule includes a fuel rod housing installed with two K-type thermocouples (TCs) in the fuel center and zircaloy cladding outer surface. The gap between the fuel pellets and cladding is filled with lead-bismuth eutectic (LBE) to reduce the thermal resistance and thereby the peak fuel temperature. This fuel rod is encapsulated in a titanium outer capsule. The assembly was designed to accommodate up to three fuel capsules and was irradiated in a center position of the MITR-II core. Neutronic and thermal analyses were performed iteratively for the final design of the HYFI facility, and installation and operation are governed by the MITR-II Technical Specifications. MCNP code was used for the neutronics analysis and FLUENT 6.3 code was used for thermal–hydraulic calculation. Initial irradiation results suggest that neutronics and thermal predictions are in good agreement with experimental results.