Structure and radiation tolerance of crystalline ceramics. The RISE-project: 241Am-doped zirconates

Spent nuclear fuel (SNF) from nuclear reactors operating worldwide will be disposed of directly or after reprocessing. In the latter case, generation of specific waste streams, e.g. minor actinide-containing waste, may require immobilization in durable, crystalline waste forms. Such candidate phases for the immobilization of (minor) actinides are various Zr(IV)-bearing solid phases like pyrochlore and zirconia. In addition to their use as potential ceramic waste matrices or inert matrix fuels for e.g. the incineration of waste plutonium, Zr-bearing phases, especially ZrO2, may be of importance as corrosion products in the dissolution of Zircaloy cladding material of SNF rods. ZrO2 is monoclinic phase (P21/c) at ambient conditions, and transforms into tetragonal (P4_2/nmc) and cubic phases (Fm3 ̅m) at high temperatures of around 1200 °C and 2370 °C, respectively. However, particle size effects, the incorporation of foreign ions such as the actinides, as well as high radiation fields are also known to influence the stability fields of the polymorphs.
This contribution provides an overview of recent studies addressing the structure, properties and the radiation tolerance of Zr(IV)-based solid phases containing actinides and their surrogates from the lanthanide series. Synthesis strategies and structural transformations taking place as a result of An(IV) or Ln(IV) incorporation in ZrO2 will be presented. Combining bulk structural characterization using powder X-ray diffraction (PXRD) with spectroscopic investigations, differences between the host- and dopant environments can be explored. In addition, radiation damage studies combining external heavy-ion irradiation of inactive Ln-doped materials and in situ self-irradiation of recently synthesized 241Am-doped Zr(IV)-phases with monoclinic, cubic defect fluorite and pyrochlore structures, will be addressed.