Vladimir M. Garbuzov

Behavior of 238 Pu-Doped Cubic Zirconia under Self-Irradiation

To investigate the resistance of cubic zirconia to accelerated radiation damage, which simulates effects of long term storage, 238 Pu-doped polycrystalline samples of cubic zirconia, (Zr,Gd,Pu)O 2 , were obtained and studied using X-ray diffraction analysis (XRD), electron probe microanalysis (EPMA), optical and scanning electron microscopy (SEM), and modified MCC-1 static leach test. The ceramic material was characterized by the following chemical composition (from EPMA in wt.% element): Zr = 50.2, Gd = 15.4, Pu = 12.2. This corresponds to the estimated formula, Zr 0.79 Gd 0.14 Pu 0.07 O 1.99 . The content of 238 Pu estimated was approximately 9.9 wt.%. The XRD measurements were carried out after the following cumulative doses (in alpha decay/m 3 × 10 23 ): 3, 27, 62, 110, 134, 188, 234, and 277. Even after extremely high self-irradiation, cubic zirconia retained its crystalline structure. All XRD analyses showed no phases other than a cubic fluorite-type structure. The following results of normalized Pu mass loss ( NL , in g/m 2 , without correction for ceramic porosity) were obtained from static leach tests (in deionized water at 90°C for 28 days) for 4 cumulative doses (in alpha decay/m 3 × 10 23 ): The results obtained confirm the high resistance of cubic zirconia to self-irradiation. This allows us to consider zirconia-based ceramic as the universal material that is suitable for actinide transmutation and geological disposal.

Synthesis of Actinide-Doped Ceramics: from Laboratory Experiments to Industrial Scale Technology

The experience of the Laboratory of Applied Mineralogy and Radiogeochemistry of the V.G.Khlopin Radium Institute on synthesis of Pu-Am-doped ceramics is summarized. During the last 5 years, dozens of actinide doped polycrystalline samples and single crystals have been successfully synthesized such as zircon, hafnon, cubic zirconia, monazite, Ti-pyrochlore, perovskite and garnet. Actinide loading has been varied as follows: - 239 Pu - from 5–6 wt.% in zircon (polycrystalline and single crystals), hafnon, garnet and perovskite to 10 wt.% in Ti-pyrochlore and up to 37 wt.% in zirconia; - 238 Pu - from 2.5 wt.% in zircon single crystals to 5 wt. % in polycrystalline zircon and 10 wt.% in monazite and cubic zirconia; - 243 Am - 20–23 wt.% in cubic zirconia and monazite. The weight of each single ceramic pellet varied from 0.2 to 2.0 grams. Special furnaces developed in KRI for ceramic synthesis allowed obtaining up to 7 ceramic pellets simultaneously during the same experiment. The highest amounts of actinides used under glove-box conditions in the same experiment were: 1.5–2.0 g for 239 Pu, 0.6 g for 238 Pu and 0.3 g for 243 Am. Most experiments on synthesis of ceramics and single crystals doped with 239 Pu, 238 Pu and 243 Am carried out at the KRI did not lead to contamination of internal walls of glove boxes. No release of Pu-Am-aerosols was observed as a result of sintering or melting at 1300–1600°C. These results allowed us to conclude that at the present the KRI has developed the experimental basis for transferring laboratory innovations to the industry of actinide immobilization. It is important that adopting ceramic synthesis methods at industrial scale does not require development of new special equipment.

Behavior of Actinide Host-Phases Under Self-irradiation: Zircon, Pyrochlore, Monazite, and Cubic Zirconia Doped with Pu-238

Crystalline ceramics are the most prospective materials suggested for the immobilization of long-lived radionulcides, in particular, weapons grade Pu and other actinides. The immobilization might include: (1) transmutation (burning) followed by geological disposal of irradiated materials or (2) just direct geological disposal of actinide matrices. Different durable host phases have been suggested for actinide (An) incorporation in the form of solid solutions. These are: different polymorphs of zirconia, (Zr,An,. . . )O2, in particular, one of cubic fluorite-type structure (Carroll, 1963; Heimann and Vandergraaf 1988); zircon, (Zr,Hf,An,. . . )SiO4 (Burakov, 1993; Ewing et al., 1995); monazite, (La,An,. . .)PO4 (Boatner et al., 1980; Boatner and Sales 1988); Ti-pyrochlore, (Ca,Gd,Hf,Pu,U)2Ti2O7 (Ebbinghaus et al., 1998) etc. To investigate the resistance of actinide host phases to accelerated radiation damage, which simulates effects of long term storage the 238Pu-doped samples of cubic zirconia and plutonia, zircon, La-monazite, Pu-monazite and Ti-pyrochlore have been repeatedly studied using X-ray diffraction analysis (XRD) and other methods. Main goal of this chapter was to summarize in comparison the principal features of different actinide host materials under self-irradiation from 238Pu. All results described in this chapter have been obtained during last several years in Laboratory of Applied Mineralogy and Radiogeochemistry of the V. G. Khlopin Radium Institute.

Inorganic matrices for immobilization of Tc-99

Immobilization of long-lived 99 Tc requires development of chemically resistant inorganic matrices. Samples of ceramics based on crystalline Fe-Mn- and Zr-Mn-oxide compounds were synthesized at 1150°C in air, reducing or inert atmosphere from precursors doped with 5-12 wt.% Tc. All the samples obtained were studied using optical and scanning electron microscopy (SEM); powder X-ray diffraction (XRD) and microprobe analysis (EMPA). Content of Tc varied from 0.5-0.8 to 3-6 wt.% in oxide host phases and from 54 to 93 wt.% in metallic inclusions. It was demonstrated that synthesis of oxide host-phases under oxidizing or reducing conditions was not optimal due to partial Tc volatilization or metallic phase formation, respectively. The use of inert atmosphere for ceramic synthesis supports Tc incorporation into crystalline structure of stable host-phases. Development of optimal methods of precursor preparation and synthesis conditions of Tc-doped ceramic are being discussed.

Nanocrystalline Layered Titanates Synthesized by the Fluoride Route: Perspective Matrices for Removal of Environmental Pollutants

Layered oxide compounds with structures based upon combinations of [TiO6] and [NbO6] octahedral building blocks attract considerable scientific and industrial interest due to their structural diversity and wide field for technological applications. The group of layered titanates is by far the best studied among this family of layered oxides (Bavykin et al. 2006; Doong and Kao 2008). In general, the crystal structures of layered titanates can be derived from the crystal structure of lepidocrocite, orthorhombic γ-FeOOH (England et al. 1983).