Structural and thermal expansion studies in ternary ThO2−CeO2−NdO1.5 system: Mimicking actinide substituted ThO2

Abstract

Abstract Utilization of vast resources of thorium in India by means of nuclear reactor and accelerator driven sub critical system (ADSS) is required to ensure the long term sustainability of nuclear power. ADSS also offers a solution to reduce long term radio-toxicity of minor actinides by their transmutation in suitable matrix. Consequently, the phase relations in ThO2–CeO2–NdO1.5 system have been investigated on slow cooled samples from 1873\u202fK in context of incineration of plutonium (Pu) and minor actinides (MAs) in ThO2 as matrix component. About 24 compositions in Th0.8Ce0.2O2−NdO1.5, Th0.8Nd0.2O1.9−CeO2 and ThO2−Ce0.5Nd0.5O1.75 series, prepared by solid state route, were characterized by X-ray diffraction (XRD) and Raman spectroscopy. CeO2 and Nd2O3 have been employed as a non-radioactive surrogate for plutonia and minor actinides, respectively, to determine solubility of Pu and MAs in ThO2. Investigation shows appearance of fluorite-type phases in thoria and ceria rich region while biphasic regime was observed for neodymia-rich region. The lattice parameters of the phases are the result of interplay of ionic radii of cations and presence of oxygen vacancies. The lattice thermal expansion behaviour of few single-phase compositions in this pseudo ternary system, as investigated by high temperature XRD, is also reported in this manuscript.