The Use of Spark Plasma Sintering for Compact Formation from Chemically Stabilised Research Reactor Fuels for Disposal

Abstract

All spent nuclear fuel requiring disposal in Canada must meet the Waste Acceptance Criteria (WAC) for the Deep Geological Repository (DGR). Oxide fuels are a robust and chemically-stable waste form, and are often the reference used for a DGR design basis. For non-oxide fuels, it is anticipated that conversion to a high density oxide form will be able to leverage the safety case for a DGR designed for oxide fuel and facilitate meeting the WAC.

The conversion pathways of various fuel forms into sintered oxide compacts suitable for disposal have been investigated. Spark Plasma Sintering (SPS), a sintering technique that employs the simultaneous application of high temperature and uniaxial pressure, has been shown to be a viable method to sinter oxidized research fuels into a stable form that should be suitable for long term disposal. Experimental efforts determined the optimum sintering pressure and temperature for compact fabrication of oxide powder derived from uranium metal, uranium carbide, and uranium oxide with alumina using graphite die tooling. It was found that increasing the number of oxidation and reduction cycles improved sinterability and ease of removal from the SPS tooling. The addition of simulated irradiated fuel powder (SIMFUEL) increased the onset sintering temperature, and a correlation with sintering temperature and density was observed (i.e., increasing sintering temperatures yielded increased densities).