ИСТИНА

Monazites are promising forms for immobilization of HLW due to ability to retain high amounts of actinides in the lattice. An important property of REE-monazites is low critical temperature of amorphisation, leading to preservation of crystallinity under reasonable levels of ion irradiation even at room temperature. Though ion irradiation studies of monazites show promising results, experimental data on self-irradiation of actinide-doped monazites are scarce. It was shown that pure Pu-monazite (PuPO4) readily amorphises due to self-irradiation, but Pu-doped REE monazites appear to be more resistant )[1]. The maximal concentration of actinides such as Pu at which the material remains stable on long timescales are still unknown. We report results of investigation of behavior of single crystals and polycrystalline monazite ceramics doped with several wt% of 238Pu on scale of up to 10 years and compare results with studies of Pu-free analogues. The samples were characterized by microprobe, vibrational spectroscopy, XAFS and X-ray diffraction. It is shown that single crystals preserve crystalline lattice despite significant doses of accumulated damage. According to XAFS data plutonium largely remains as isomorphic impurity. On surfaces of Pu-doped crystals whitish secondary phases were formed. Spectroscopic data indicates that the white phase represents distorted, but still crystalline monazite.