Crystal Chemistry of Titanates and Zirconates of Rare Earths—Possible Matrices for Actinide Isolation

Yudintsev, S. V.; Nickolsky, Maximilian S.; Stefanovskaya, O. I.; Никонов, Б. С.

doi:10.1134/s1066362222060017

Cited by 3 publications

(2 citation statements)

References 58 publications

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“…Stable elements or U and Th with a long half-life and low heat release are usually used in the laboratory synthesis and study of high-level waste matrices. For trivalent MAs (Am, Cm), REEs serve as simulants (Table 6); most often, Nd [22,23]. This approach is based on the proximity of the radii of Nd 3+ , Am 3+ , and Cm 3+ [24].…”

Section: Effect Of Radiogenic Heat On the Vitreous Matrix Of The Ree-...mentioning

confidence: 99%

Thermal Effects and Glass Crystallization in Composite Matrices for Immobilization of the Rare-Earth Element–Minor Actinide Fraction of High-Level Radioactive Waste

Yudintsev,

Ojovan,

Malkovsky

2024

J. Compos. Sci.

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The current policy of managing high-level waste (HLW) derived in the closed nuclear fuel cycle consists in their vitrification into B-Si or Al-P vitreous forms. These compounds have rather limited capacity with respect to the HLW (5–20 wt%), and their properties change over time due to devitrification of the glasses. Cardinal improvement in the management of HLW can be achieved by their separation onto groups of elements with similar properties, followed by their immobilization in robust waste forms (matrices) and emplacement in deep disposal facilities. One of the possible fractions contains trivalent rare-earth elements (REEs) and minor actinides (MAs = Am and Cm). REEs are the fission products of actinides, which are mainly represented by stable isotopes of elements from La to Gd as well as Y. This group also contains small amounts of short-lived radionuclides with half-lives (T1/2) from 284 days (144Ce) to 90 years (151Sm), including 147Pm (T1/2 = 2.6 years), 154Eu (T1/2 = 8.8 years), and 155Eu (T1/2 = 5 years). However, the main long-term environmental hazard of the REE–MA fraction is associated with Am and Cm, with half-lives from 18 years (244Cm) to 8500 years (245Cm), and their daughter products: 237Np (T1/2 = 2.14 × 106 years), 239Pu (T1/2 = 2.41 × 104 years), 240Pu (T1/2 = 6537 years), and 242Pu (T1/2 = 3.76 × 105 years), which should be immobilized into a durable waste form that prevents their release into the environment. Due to the heat generated by decaying radionuclides, the temperature of matrices with an REE–MA fraction will be increased by hundreds of centigrade above ambient. This process can be utilized by selecting a vitreous waste form that will crystallize to form durable crystalline phases with long-lived radionuclides. We estimated the thermal effects in a potential REE–MA glass composite material based on the size of the block, the content of waste, the time of storage before immobilization and after disposal, and showed that it is possible to select the waste loading, size of blocks, and storage time so that the temperature of the matrix during the first decades will reach 500–700 °C, which corresponds to the optimal range of glass crystallization. As a result, a glass–ceramic composite will be produced that contains monazite ((REE,MA)PO4) in phosphate glasses; britholite (Cax(REE,MA)10-x(SiO4)6O2) or zirconolite ((Ca,REE,MA)(Zr,REE,MA)(Ti,Al,Fe)2O7), in silicate systems. This possibility is confirmed by experimental data on the crystallization of glasses with REEs and actinides (Pu, Am). The prospect for the disposal of glasses with the REE–MA fraction in deep boreholes is briefly considered.

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Section: Effect Of Radiogenic Heat On the Vitreous Matrix Of The Ree-...mentioning

confidence: 99%

Thermal Effects and Glass Crystallization in Composite Matrices for Immobilization of the Rare-Earth Element–Minor Actinide Fraction of High-Level Radioactive Waste

Yudintsev,

Ojovan,

Malkovsky

2024

J. Compos. Sci.

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“…Zirconolite, like its structural relative pyrochlore, has a high capacity for iso-and heterovalent exchanges involving REE, actinides, and small ions with a charge of 2+ to 5+ to compensate for the lattice charge. This distinguishes it from the Nd 2 TiO 5 , Nd 2 Ti 2 O 7 , and Nd 4 Ti 9 O 24 phases, another group of possible matrices for the immobilization of the REE-MA fraction [126].…”

Section: Crystal Chemistry Of Zirconolite and Its Polytypementioning

confidence: 99%

Zirconolite Matrices for the Immobilization of REE–Actinide Wastes

et al. 2023

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The structural and chemical properties of zirconolite (ideally CaZrTi2O7) as a host phase for separated REE–actinide-rich wastes are considered. Detailed analysis of both natural and synthetic zirconolite-structured phases confirms that a selection of zirconolite polytype structures may be obtained, determined by the provenance, crystal chemistry, and/or synthesis route. The production of zirconolite ceramic and glass–ceramic composites at an industrial scale appears most feasible by cold pressing and sintering (CPS), pressure-assisted sintering techniques such as hot isostatic pressing (HIP), or a melt crystallization route. Moreover, we discuss the synthesis of zirconolite glass ceramics by the crystallization of B–Si–Ca–Zr–Ti glasses containing actinides in conditions of increased temperatures relevant to deep borehole disposal (DBD).

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Photoluminescence and supercapacitor applications of dysprosium doped rhombohedral silver gallium oxide nanoparticles

Chalvan,

N.,

Manjunatha

et al. 2024

Materials Today Sustainability

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Crystal Chemistry of Titanates and Zirconates of Rare Earths—Possible Matrices for Actinide Isolation

Cited by 3 publications

References 58 publications

Thermal Effects and Glass Crystallization in Composite Matrices for Immobilization of the Rare-Earth Element–Minor Actinide Fraction of High-Level Radioactive Waste

Thermal Effects and Glass Crystallization in Composite Matrices for Immobilization of the Rare-Earth Element–Minor Actinide Fraction of High-Level Radioactive Waste

Zirconolite Matrices for the Immobilization of REE–Actinide Wastes

Photoluminescence and supercapacitor applications of dysprosium doped rhombohedral silver gallium oxide nanoparticles

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