Devon Drey, Robby Kile, and Ed Duchnowski are among the latest winners of the 2021 Innovations in Nuclear Technology Research and Development Awards sponsored by the US Department of Energy, Office of Nuclear Energy, Office of Nuclear Fuel Cycle and Supply Chain.
Devon Drey won first place in the “Material Recovery and Waste Form Development” category for his research on complex oxide pyrochlore, which is being investigated as a potential material for the immobilization of nuclear waste isotopes and is a key component of proposed nuclear waste forms like Synroc. Pyrochlore’s chemical and structural flexibility makes it suitable for the incorporation of a large variety of atomic species directly into its crystal lattice; lattice immobilization is a more reliable method for storing long-lived radioactive isotopes.
Pyrochlore can accommodate large atoms like uranium, plutonium, transplutonic actinides, lanthanides, and transition metals, covering a large portion of the nuclear waste species produced in the fuel cycle. Pyrochlore oxides disorder and/or amorphize from external or self-irradiation and so understanding defect formation mechanisms in pyrochlore is key to its safe use as a nuclear waste form.
“I study oxide ceramics in Dr. Maik Lang’s group, where we subject these ceramics to intense radiation and see what happens to the atomic structure,” said Drey. “Since these ceramics are used in a wide variety of important applications, from nuclear fuel to waste disposal to space technology, it is critical that we understand the damage to these ceramics that occur under irradiation so that we can safely use them. Being so close to ORNL gives us access to some of the most advanced technology in the world to study these damaged materials, atom by atom.”
Drey’s publication uses advanced neutron and X-ray total scattering techniques, as well as high temperature melt solution calorimetry, to describe disordering and defect formation in the pyrochlore solid solution series Ho2Ti1-xZrxO7. The fundamental science detailed in this paper will be used to understand radiation resistance in other pyrochlore compounds of interest for waste immobilization.
Kile’s research involves modeling two different transient scenarios: a reactivity-initiated incident, and a pressurized loss of forced cooling incident. His findings demonstrated that even in extremely severe events, the TCR fuel is expected to remain intact, preventing the release of radioactive material.
Kile conducted sensitivity and uncertainty studies, which entailed creating thousands of models for transients, varying different design and incident parameters to understand which parameters had the greatest impact on reactor performance. He then passed that information back to the TCR design team, who could use it to identify which areas of the design needed more focus for optimizing the final design.
The design of the TCR was created to take advantage of these benefits of modern manufacturing capabilities. After a design was created, the TCR design team at ORNL and researchers at UT built computer models of the design and ran simulations of both normal operating conditions and transient scenarios to understand how a given design would perform.
Duchnowski’s research pertains to the High Temperature Gas-Cooled Reactor (HTGR), which is a Generation IV type of nuclear reactor that has applications beyond power generation and is designed around safety. HTGRs have challenges associated with the moderating material, which is responsible for reducing neutron energies to levels necessary for fission.
HTGRs have historically used graphite, but under irradiation graphite has limitations on the allowable operational time before needing to be replaced. It was proposed that alternatives to graphite that consist of a two-phase composite would mitigate this issue while simultaneously improving reactor performance.
An assessment on reactor performance and safety characteristics was conducted and concluded that two-phase composite moderators have the potential for enhanced reactor performance and potentially longer in-service lifetime operation. Furthermore, accident analysis shows that no expected compromise in the reactor core is expected while utilizing alternative moderators.