Application of SPS in the fabrication of UN and (U,Th)N pellets from microspheres

L.G Gonzalez Fonseca,M Hedberg,L Huan,P Olsson,T Retegan Vollmer

doi:10.1016/j.jnucmat.2020.152181

L.G Gonzalez Fonseca, M Hedberg + Show 3 more

Open Access

https://doi.org/10.1016/j.jnucmat.2020.152181

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Abstract

In this study, the process involved in the fabrication of a potential accident tolerant fuel is described. Homogeneous uranium nitride microspheres doped with different thorium content were successfully manufactured using an internal gelation process followed by carbothermic reduction, and nitridation. Elemental analysis of the materials showed low carbon and oxygen content, the two major impurities found in the products of carbothermic reduction. Uranium nitride microspheres were pressed and sintered using spark plasma sintering (SPS) to produce pellets with variable density. Final density can be tailored by choosing the sintering temperature, pressure and time. Density values of 77–98% of theoretical density (%TD) were found. As expected, higher temperatures and pressures resulted in a denser material. Furthermore, a direct correlation between the onset sintering temperature and thorium content in the materials was observed. The change of onset temperature has been related to an increment in the activation energy for self-diffusion due to the substitution of uranium atoms by thorium in the crystal structure.

Highlights

After Fukushima Daiichi nuclear accident, international efforts have been focused on manufacturing fuels that can withstand accident conditions for an extended period of time
In this work uranium nitride (UN) and (U,Th)N pellets were prepared by spark plasma sintering (SPS) using microspheres as feed material, which has not been reported previously
Internal gelation process followed by carbothermic reduction provided a reliable method to manufacture UN and (U,Th)N microspheres

Summary

Introduction

After Fukushima Daiichi nuclear accident, international efforts have been focused on manufacturing fuels that can withstand accident conditions for an extended period of time. Such fuel concepts are known as Accident Tolerant Fuels (ATF). These materials must exhibit the same or improved properties compared to current fuels while reducing oxidation kinetics and hydrogen production rates under accident conditions [1,2]. Fuel Thermal conductivity (W/mK: 600e1400K) Melting point (K) Peak centerline temperature (K) Density (g/cm3) Uranium density in the compound (g/cm3) [8]. Uranium density in UN, U3Si2, and UC is higher compared to UO2, which could allow an extended fuel cycle length or reduction of the otherwise required enrichment

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