To investigate the behavior of monazite during accelerated radiation damage, which simulates effects of long term storage, 238 Pu-doped polycrystalline samples of (La,Pu)PO 4 and PuPO 4 were synthesized for the first time ever and studied using powder X-ray diffraction (XRD) analysis and optical microscopy. The starting precursor materials were obtained by precipitation of La and (or) Pu from their aqueous nitrate solutions followed by calcination in air at 700°C for 1 hour, cold pressing, and sintering in air at 1200-1250°C for 2 hours. The 238 Pu contents in ceramic samples measured using gamma spectrometry were (in wt.% el.): 8.1 for (La,Pu)PO 4 and 7.2 for PuPO 4 . The (La,Pu)PO 4 monazite remained crystalline at ambient temperature up to a cumulative dose of 1.19 x 10 25 alpha decays/m 3 . In contrast, the PuPO 4 monazite became nearly completely amorphous at a relatively low dose of 4.2 x 10 24 alpha decays/m 3 . Swelling and crack formation due to the alpha decay damage was observed in the PuPO 4 ceramic. Also, under self-irradiation this sample completely changed color from initial deep blue to black. The (La,Pu)PO 4 monazite was characterized by a similar change in color from initial light blue to gray, however, no swelling or crack formation have so far been observed. The results of this study allow us to conclude that the radiation damage behavior of monazite strictly depends on the chemical composition. The justification of monazite-based ceramics as actinide waste forms requires additional investigation.
In order to obtain Pu-doped zircon, (Zr,Pu)SiO 4 , with a maximum Pu content in the form of solid solution, zircon single crystals have been grown using the flux method from starting materials overloaded with Pu. The crystals obtained ranged from 0.2-0.5 to 3.5-4.5 mm in size, are transparent, and characterized by deep pink-brown color. No inclusions of separate Pu phases were observed in the crystals. The distribution of Pu in crystals is zoned and the Pu content varying from approximately 5 to 14 wt.% el. The zircon unit cell parameters calculated from XRD data of bulk powdered sample were: a=6.620(1); c=5.989(2). The results obtained allow us to conclude that the capacity of the zircon structure to incorporate Pu exceeds 10 wt.% el.; however, additional research is required to study the extent of solid solution, (Zr,Pu)SiO 4 , at higher Pu contents.
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