Lattice parameter expansion by self-irradiation damage of ²⁴⁴Cm-²⁴⁰Pu oxide and mononitride

The lattice parameter expansion induced by self-irradiation damage was measured on the powder of (Cm_0.4, Pu_0.6)O_2-x and (Cm_0.4, Pu_0.6)N by X-ray diffraction at room temperature. The starting material of (Cm_0.4, Pu_0.6)O_2-x had an single phase with a fluorite fcc structure. Three oxide samples for XRD measurements were obtained by annealing the starting material at 643 and 1073 K in air, and 1497 K in argon, respectively. The undamaged lattice parameters a_o of the annealed oxides were estimated to be 0.5395, 0.5388 and 0.5479 nm. The lattice parameter expansion of each sample almost saturated within ∼5 days after annealing. The saturated Δa/a_o were 2.5x10^-3, 2.7x10^-3 and 1.4x10^-3 for each samples. The solid solution of mononitride was prepared from the oxide by carbothermic reduction method. The a_o value was estimated to be 0.4945 nm after annealing at 1473 K in N₂+4%H₂ mixed gas stream. The saturated Δa/a_o for the nitride was 3.4x10^-3. Saturation of Δa/a_o for all the samples were expected to be achieved when λt (λ: decay constant) reached to 2-3x10^-4 like other pure dioxides of Pu and Cm. (author)