effect of stoichiometry on the structural and chemicalstability of diborides for use in nuclear fuels
J.T.P. Wachsmann1, S.C. Middleburgh2, R. Holmes2, D. Chavara2, G.R. Lumpkin2, L. Hallstadius3, A. Ruys1
1University of Sydney, Darlington, 2006, Australia;
2ANSTO, Lucas Heights, 2234, Australia.
3Westinghouse Electric Sweden, Västerås, Sweden
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Binary borides are emerging as candidate materials for components in a variety of industries due to their high temperature stability and other interesting properties. In particular, their application to the nuclear industry as a neutron control material is of significant interest and as such research into the properties of diborides has important technological implications.
Boron compounds have been used to control the reactivity of nuclear reactors since the beginning of nuclear power generation. Boron-10 has a very large neutron cross-section, strongly absorbing both fast and thermal neutrons. Importantly, upon absorbing a neutron B-10 transforms into He-4 and Li-7, both of which have very low neutron cross-sections, minimising parasitic neutron absorbance and inefficient use of the remaining fuel. Incorporating boron such that it survives the sintering environment and reactor operation with no adverse effects on the fuel has been a major challenge for the industry.
This work investigates the effect of stoichiometry and processing variations on the porosity and microstructure of manufactured zirconium diboride and titanium diboride. A great deal of our work investigated the corrosion behaviour of the materials to consider their potential use in molten salt reactors. They were examined by exposing the various manufactured samples to fluoride based molten salts which are expected to be utilised in next generation reactors. These samples were then characterized using a range of techniques to highlight the key failure mechanisms of the ceramic.
Inherent to the role of a burnable poison is the consumption of boron within the material. As a result, our research extends to understand the behaviour of binary diborides with compositional variation, which are of great interest not only to the nuclear industry but also to the scientific community and other high technology industries.