Insight into thorium dioxide could provide new energy applications

In the field of nuclear fuels, thorium dioxide has long been the understudied sibling in the family of actinide and lanthanide fluorite oxides, despite its advantageous high melting point. But now, advances in single crystal thorium dioxide production and ion beam processing have allowed scientists to study the effects of material defects on thermal transport at small scales.

Until recently, researchers were only able to study sintered ceramic thorium dioxide. The material’s porosity makes it hard untangle effects specifically due to smaller-scale defects. To overcome this issue, Dennett et al. studied large single crystals in order to understand the effects of nanoscale lattice defects on thermal transport, which in other materials is known to have outsized impacts on the thermal transport performance.

“With these new single crystals, we think we can get to really some of the basic understanding the community has been lacking for a while,” said author Cody Dennett.

Using an ion beam, the researchers irradiated a thorium dioxide crystal to create defects in the material. Areas of the crystal were locally heated with lasers, and a specially designed thermoreflectance instrument was used to study thermal transport on small scales of tens of micrometers. They found that the transport was limited at much lower radiation exposures than expected, yet still higher than in the most common nuclear fuel, uranium dioxide.

The group is continuing their studies with lower defect levels, but the initial results provide important insight into the possibilities of using thorium dioxide in mixtures or as a dopant in next-generation nuclear fuels. Its large electronic bandgap also makes it a promising candidate for future device physics applications.

Source: “The influence of lattice defects, recombination, and clustering on thermal transport in single crystal thorium dioxide,” by Cody A. Dennett, Zilong Hua, Amey Khanolkar, Tiankai Yao, Phyllis K. Morgan, Timothy A. Prusnick, Narayan Poudel, Aaron French, Krzysztof Gofryk, Lingfeng He, Lin Shao, Marat Khafizov, David B. Turner, J. Matthew Mann, and David H. Hurley, APL Materials (2020). The article can be accessed at https://doi.org/10.1063/5.0025384 .