PRE-HALTED (Preparatory Experiments for Halden Thermal properties Experimental Determination)

Purpose and goal:

The thermal properties (particularly thermal conductivity, TC) are crucial for the safety and performance of nuclear fuel under both normal and off-normal conditions. TC varies with burnup and locally over the diameter of the fuel pellet. It is difficult to remove the pellet from the cladding for measurement using traditional methods.

New fuel types being developed globally need experimental measurements of their thermal properties after irradiation. A new method has been developed and qualified to measure the thermal properties of irradiated fuel without removing the cladding. Expected results and effects:

Direct measurements of thermal conductivity (TC), thermal diffusivity (TD) and specific heat capacity were performed on a set of commercial nuclear fuel pellets using a Transient Hot Disk (THD) TPS instrument at room temperature with and without simulated cladding. The work resulted in a sample preparation and testing procedure that provides a robust, reproducible and relatively inexpensive method adapted for future application to unirradiated or irradiated fuel samples for an international market.

Approach and implementation:

Unirradiated pellets of different compositions were prepared in the same way as irradiated fuel in hot cells, with fixtures adapted for this specific application. They were then systematically measured with and without cladding, using different sensors, measurement settings and other parameter variables to assess the performance of the method. The measurement results were compared with published data using other methods.

TC and TD were determined from repeated measurements with different settings and measurement procedures, to evaluate the method accuracy and precision.