This work will be the first application of the thermal conductivity microscope (TCM) to sodium fast reactor (SFR) mixed oxide fuel (MOX). The benefit of using the TCM compared to standard laser flash analysis used on fuel is that the TCM is able to spatially resolve the local thermal conductivity at a resolution in the range of 50-100 micrometers. At high burnup of MOX, extensive migration of fission products towards the fuel to cladding gap occurs, which forms the so-called “Joint Oxide Gaine” or JOG. Using the TCM, the radial distribution of thermal conductivity can be determined and correlated to the elemental composition and underlying microstructure that resulted from a previous RTE (RTE #18-1452). Because the SFR MOX has been irradiated, the TCM is the only facility in the world that can perform these measurements. The scope of the project (1.5 days sample preparation of existing sample at the Irradiated Materials Characterization Laboratory, and 6 days of TCM measurements) is within the scale of an RTE and would provide first-of-its-kind data on the thermal conductivity of irradiated MOX fuel.

This project benefits both the Advanced Fuels Campaign (AFC) and the Nuclear Energy Advanced Modeling and Simulation (NEAMS) program. Extensive characterization of the properties of fuels envisaged for advanced fuel cycles is of key importance to assess the performance of these fuels. The measurements would offer not only insight into the link between local microstructure and thermal conductivity evolution in reactor irradiated MOX but would also establish a validation data set for various codes. These include lower length scale MD and DFT simulations, as well meso-scale codes such as MARMOT and are critical components of the DOE’s Multiphysics Object Oriented Simulation Environment (MOOSE). One peer-reviewed scientific publication will be written, based on the experimental data produced in this work.