Development and Characterization of (Semi-)Clathrate Hydrates for Capture and Separation of 85Kr and Xe from Nuclear Reactor Off-Gas Streams

The overarching goal is to develop and characterize novel clathrate and semi-clathrate hydrate compounds for efficient capture and separation of 85Kr and Xe from off-gas streams generated as fission products during nuclear reactor irradiation. We will execute this research in an iterative manner using a combination of various experimental as well as modeling methods. First, Kr and Xe hydrate samples will be synthesized at moderately high-pressure (P) and/or low-temperature (T) conditions. Crystal structure, chemical bonding, thermodynamics and kinetics of hydrate formation will then be characterized using a suite of in situ real-time experimental techniques including X-ray/neutron diffraction, Raman spectroscopy, inelastic neutron scattering coupled with molecular dynamics simulations, and calorimetry. The systematic studies will reveal fundamental relations among chemical composition, crystal structure, coordination chemistry, thermodynamic stability, and formation kinetics of Kr- and Xe-bearing hydrates at relevant P-T conditions. Lastly, based on the obtained chemistry-structure-stability relations, we will modify the hydrate compositions by doping thermodynamic promoters (organic molecules or salts) and thus develop novel (semi-)clathrate compounds that can be stabilized at mild P-T (close to ambient) conditions while potentially incorporating other volatile radionuclides, especially 129I. This research will fill critical knowledge gaps in fundamental understanding of the relationships among chemistry, structure, and formation thermodynamics/kinetics of Kr/Xe-bearing (semi-)clathrate hydrates at relevant P-T conditions. By doing so, we will develop novel (semi-)clathrate hydrate compounds: 1) with optimal phase stability at close-to-ambient conditions (e.g., >280 K,