Abstract: The disclosed technology can be implemented to provide a method of determining a thermal conductivity of a sample. The method includes controlling a thermal source to increase a temperature of the thermal source to an elevated temperature above a phase change temperature of a phase change material, placing the sample between and in thermal contact with the phase change material below the phase change temperature and the thermal source to allow a thermal conduction from the thermal source to the phase change material through the sample to increase an initial temperature of the phase change material to the phase change temperature to cause the phase change material to transition from a first phase to a second phase, performing a measurement on at least one of the sample or the phase change material, and determining the thermal conductivity of the sample based on the measurement.

Abstract: Fuel rod designs and techniques are provided to encapsulate nuclear fuel pellets in nuclear fuel rods. The tubular cladding in the disclosed fuel rods includes silicon carbide and a metal filler structure formed of a metal that becomes molten during a nuclear reaction of the nuclear fuel pellets and located inside the tubular cladding to include a metal tube that fills in a gap between the nuclear fuel pellets and an interior side wall of the tubular cladding and structured to include a closed metal end cap at one end of the nuclear fuel pellets to leave a space between one end of the interior of the tubular cladding and the closed metal end cap of the metal filler structure as a reservoir.