High temperature validation of a line heat source technique for in-pile thermal conductivity determination

In-pile instrumentation is critical for advancing operations and materials discovery in the nuclear industry. Ensuring optimal performance of sensors in high temperatures is the first step in demonstrating their viability in the harsh in-pile environment. This work demonstrates the high temperature capabilities of a line heat source and measurement technique previously shown to extract thermal conductivity of nuclear fuel sized samples within a laboratory environment at room temperature. This method uses a hybrid AC/DC measurement technique to obtain rapid measurements of the temperature dependent voltage change of a heater wire, which also acts as a resistance thermometer. Once the temperature profile of the heating element is extracted it is matched to a multilayered analytical model to determine the thermal conductivity of the sample. Measurements are conducted over a range of temperatures to extract the thermal conductivity as a function of temperature for 10 mm diameter 6061 aluminum samples. Each measurement had a coefficient of correlation (R2) value higher than 0.995 when matched to its corresponding analytical model. The thermal diffusivity values for each temperature are also identified and reported. Microstructure analysis was also conducted to further characterize the material measured.