The Complexitiy and Intricacy of the Materials Chemistry in Additive Doped-UO₂ Fresh and Spent Nuclear Fuel

Additive doped-UO₂ nuclear fuels have become increasingly popularised due to the enhanced operational safety benefits they possess over traditional non-doped forms. The addition of additives such as Al, Nd, Mg, Mn and particularly Cr among others into UO₂ during fuel fabrication has been demonstrated to result in significantly enhanced grain growth that enables enhanced fission gas retention during reactor operations. Subsequently, this enables the fuel to remain within the reactor for extended burnup periods and better enable it to respond to transient events leading to these fuel variants to fall under the accident tolerant (ATF) class. Despite the prolific interest in such fuel varieties from industry and researchers alike, significant gaps exist in the fundamental materials chemical understanding of these fuels. For instance, a description of the chemical-redox states that occur within Cr-doped UO₂ has remained contentious until only recently [1]. Such a lack of basic knowledge arises through the complexity of chemical states that additives can adopt within the fuel matrix. This complexity is further exacerbated when one considers the complex chemistry that arises when additive doped-UO₂ fuel varieties are discharged from reactors as spent nuclear fuel (SNF). Studying SNF is challenging due to the heightened radioactivity of these materials, restricting their investigation to few specialised nuclear laboratories. Our group has devoted significant efforts to investigating additive doped-UO₂ materials using model system studies involving the synthesis of representative specimens that are relevant to industry standards and subjecting them to high resolution spectroscopic investigation. Our experimental investigations, often performed synergistically with simulation methods, have enabled a precise and detailed chemical description of additive doped-UO₂materials as fresh fuels and further provided insight into their behaviour as SNF. Accordingly, this presentation will discuss these recent endeavours in a “cradle to the grave” approach including (i) the role of secondary phases in facilitating or inhibiting grain growth during sintering (ii) comparative analysis of extracted single crystal grains against bulk material to deconvolute chemical states in fresh fuel and (iii) formation of additive specific solid phases in SNF and their response to radiation damage through experimental and simulation methods.<br/><br/><br/>&lt;!--[if supportFields]&gt;&lt;span style='font-size: 9.0pt;font-family:"Arial",sans-serif'&gt;&lt;span style='mso-element:field-begin'&gt;&lt;/span&gt;&lt;span style='mso-spacerun:yes'&gt; &lt;/span&gt;ADDIN EN.REFLIST &lt;span style='mso-element: field-separator'&gt;&lt;/span&gt;&lt;/span&gt;&lt;![endif]--&gt;[1] G.L. Murphy, R. Gericke, S. Gilson, E.F. Bazarkina, A. Rossberg, P. Kaden, R. Thümmler, M. Klinkenberg, M. Henkes, P. Kegler, V. Svitlyk, J. Marquardt, T. Lender, C. Hennig, K.O. Kvashnina, N. Huittinen, Deconvoluting Cr states in Cr-doped UO2 nuclear fuels via bulk and single crystal spectroscopic studies, Nature Communications 14(1) (2023) 2455.<br/>&lt;!--[if supportFields]&gt;&lt;span lang=EN-GB style='font-size:9.0pt;font-family: "Arial",sans-serif;mso-fareast-font-family:SimSun;mso-ansi-language:EN-GB; mso-fareast-language:EN-US;mso-bidi-language:AR-SA'&gt;&lt;span style='mso-element: field-end'&gt;&lt;/span&gt;&lt;/span&gt;&lt;![endif]--&gt;