Technological problems and the future of research on the basic properties of actinide oxides

Characterization and densification studies on ThO2–UO2 pellets derived from ThO2 and U3O8 powders

“…ThO 2 is the only stable oxide of Th-O system in the condensed state and it has very little non-stoichiometry compared to UO 2 . Th 4+ is the only valence state of thorium [39][40][41]. U 3 O 8 is one of the most kinetically and thermodynamically stable forms of uranium [6,42,43].…”

Thermal diffusion of iodine in UO2 and UO2+x

“…Furthermore, the population of uranium lattice vacancies increases rapidly as a function of the degree of hyperstoichiometry [11,12]. Because the combined average valence of the fission products is slightly less than four (plutonium fission is more oxidizing than uranium fission), an incremental excess of oxygen can develop within the fuel matrix as a function of extended burnup [1,37], whereas any failure of the sheath would lead to significant oxidation of the fuel [1][2][3]. Fig.…”

“…Moreover, release of radionuclides from defected fuel elements during reactor operation contributes to activity transport and occupational radiation exposures [3]. Accumulation of segregated fission products at the fuel grain boundaries and at the fuel-sheath interface also enhances the potential for release of radioactivity to the environment in the event of an accident and from spent fuel during storage or after permanent disposal [2][3][4]. Despite the significant progress that has been achieved over the past half century in understanding the properties of oxide nuclear fuels, there is still considerable uncertainty in the migration behaviour of several key fission products [1][2][3][4].…”

“…Segregation of fission products with low solubility in uranium dioxide is a determining factor for performance and safety throughout the nuclear fuel cycle [1][2][3][4]. At high burnup, release of inert fission gases from the fuel matrix can be sufficient to cause overpressure strain of the fuel sheath (cladding).…”

Characterization of (Th,U)O2 pellets made by advanced CAP process

“…ThO 2 is the only stable oxide in the Th-O system in the condensed phase and it has very little non-stoichiometry compared to UO 2 [12][13][14]. Hence, the defect concentration in ThO 2 is low.…”