Self‐Radiation Damage in Curium‐244 Oxide and Aluminate

Abstract

Self-radiation from d e c a y of "Cm causes lattice swelling, phase transformations, and loss of structure in several Cm compounds. In Cm oxides, the percentage swelling at saturation decreases with decreasing symmetry: Swelling in fluorite (fcc) CmO, (~0 . 3 % ) is approximately twice that in bcc C-type CmO,; monoclinic Cm,O, does not swell. CmO, swells with time according to Aa/a=t. Ox 103(1 -e -1 .~x l o ' A t ) , essentially the same relation as for PuO, and AmO,. The rate of structure loss of Cm oxides decreases with increasing temperature of prior heatings. In CmAlO, the metamict state is produced before swelling reaches saturation. Radiation-induced transformation at room temperature produces metastable phases that normally exist at higher temperatures, e.g. bcc C-type Cm,O, transforms to hexagonal A-type Cm,O, and rhombohedral CmAlO, becomes cubic.

Structural investigation on an aged americium transmutation fuel

“…The X-ray diffraction results for CmAlO 3 indicate a local increase in symmetry prior to amorphization [11]. A similar effect was found for the first oxygen shell in zircon doped with 238 Pu [17].…”

“…The three oxygen sub-shell contributions to the EXAFS partially cancel each other out, resulting in a broad FT peak with low intensity. As indicated from X-ray diffraction investigations on 244 CmAlO 3 , the rhombohedral material becomes cubic upon self-irradiation before total amorphization occurs [11]. In a cubic perovskite structure the first oxygen coordination shell does not exhibit static disorder.…”

“…For CmAlO 3 this transition is reported below 773 K [11]. Mosley [11] also indicated that self-irradiation damage swells the 244 CmAlO 3 lattice, which stabilizes the cubic structure at room temperature before it becomes amorphous.…”

“…As indicated by neutron diffraction, LaAlO 3 becomes cubic above 820 K, whereas the rhombohedral to cubic transition temperature of NdAlO 3 seems to be higher than 1673 K [13]. For CmAlO 3 this transition is reported below 773 K [11]. Mosley [11] also indicated that self-irradiation damage swells the 244 CmAlO 3 lattice, which stabilizes the cubic structure at room temperature before it becomes amorphous.…”

“…Distortion increases within the lanthanide series and from SmAlO 3 to LuAlO 3 the less symmetric orthorhombic structure Pbnm is stable at room temperature [7,8]. PuAlO 3 , AmAlO 3 , CmAlO 3 crystallize in the rhombohedral space group R 3c [9][10][11]. The AmAlO 3 lattice parameters were reported as a = 5.336 (5) and c = 12.91 (2) Å , but no information about the atomic positions are available [10].…”