In the present study, we examine the effect of point defects and fission gases on thermal transport in representative actinide oxides used in modern reactors. In particular, oxygen interstitials and Kr/Xe fission gas bubbles are of primary focus. Reverse non-equilibrium molecular dynamics is employed to investigate thermal transport in UO2 and PuO2 with oxygen interstitials at the defect concentrations of 0.1%, 1%, and 5%. The results show that any alteration to the lattice structures of these fuels reduce their thermal conductivities significantly. For the largest UO2 structure simulated in the present study, for example, 0.1% oxygen interstitials decreased the thermal conductivity by 18.6%. For the case of the effect of fission gas bubbles, serious modification to phonon dispersion in oxide fuels is caused by the presence of a single fission gas bubble, resulting in a large temperature drop in their temperature profiles. The average interfacial thermal resistance across a fission gas bubble (comprised of 30 Kr and/or Xe atoms) is estimated to be 2.1 × 10−9 Km2/W.
Multi-layered carbon nanostructures are the next leap for many advanced consumer and industrial applications that require both high strength and uniquely high electrical and thermal properties. Applications of three-dimensional (3D) carbon nanostructures have already been theorized to include wearable technology, processor chip heat transfer material, and flexible electronics. 3D carbon nanostructures appear in the form of carbon nanotubes (CNTs) and layered graphene tiers, however, many structures previously examined have been limited to one or two graphene layers or non-repeatable structured patterns. Many of the electrical and thermal properties of CNTs are still being investigated, but the initial studies demonstrate promising results such as the thermal conductivity ranging in the thousands W/m-K. Developing new ways to fabricate these structures at a reasonable cost has become a primary focus for graphene-based research. In this study, 3D carbon nanostructure samples are 3D printed using laser lithography, then a series of high temperature furnace burns and Nickel Chemical Vapor Deposition (CVD) is utilized to leave a previously multi-species structure as a solely carbon-species structure with mostly carbon sp-2 bonds. CVD has proven to be a leading method for forming graphene due to the ability to control graphene nucleation across larger surfaces and structures. Nanoscale 3D printing of carbon structures also allows for a great degree of freedom towards the creation of repeatable patterns or structures that are currently trying to be achieved in other studies. This study employs the use of controlled cleanroom environments with cutting edge technology and machines to fabricate the 3D carbon nanostructures.
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