Rare earth(RE)-containing crystals have been investigated as media for the immobilization of RE fission products from nuclear waste streams.During reprocessing of spent nuclear fuel,fission products including REs,alka...Rare earth(RE)-containing crystals have been investigated as media for the immobilization of RE fission products from nuclear waste streams.During reprocessing of spent nuclear fuel,fission products including REs,alkalis,and alkaline earths released from the fuel.One viable option to immobilize the RE fission products is to incorporate them into chemically durable crystalline phases in specific waste forms.This study summarizes the crystal structures and synthesis methods of six RE-containing compounds that have applications in remediation of RE fission products.These compounds include oxyapatite(AE_(2)RE_(8)(SiO_(4))_(6)O_(2)),oxychloride(REOCl),borosilicate(RE_(3)BSi_(2)O_(10)),pyrochlore(RE_(2)M_(2)O_(7)),monazite(REPO_(4)),and perovskite(REMO_(3))where AE denotes alkaline earth metals and M denotes transition metals.This review provides an overview of literature on the usage of these six compounds for immobilizing RE fission products and summarizes different synthesis methods for producing these compounds.Comparisons of structural parameters with different REs in each compound are also discussed.展开更多
Perovskite-based ceramic composites were developed as potential waste form materials for immobilizing cesium(Cs)and iodine(I)with high waste loadings and chemical durability.The perovskite Cs_(3)Bi_(2)I_(9)has high Cs...Perovskite-based ceramic composites were developed as potential waste form materials for immobilizing cesium(Cs)and iodine(I)with high waste loadings and chemical durability.The perovskite Cs_(3)Bi_(2)I_(9)has high Cs(22 wt%)and I(58 wt%)content,and thus can be used as a potential host phase to immobilize these critical radionuclides.In this work,the perovskite Cs_(3)Bi_(2)I_(9)phase was synthesized by a cost effective solution-based approach,and was embedded into a highly durable hydroxyapatite matrix by spark plasma sintering to form dense ceramic composite waste forms.The chemical durabilities of the monolithic Cs_(3)Bi_(2)I_(9)and Cs_(3)Bi_(2)I_(9)-hydroxyapatite composite pellets were investigated by static and semi-dynamic leaching tests,respectively.Cs and I are incongruently released from the matrix for both pure Cs_(3)Bi_(2)I_(9)and composite structures.The normalized Cs release rate is faster than that of I,which can be explained by the difference in the strengths between Cs-I and Bi-I bonds as well as the formation of insoluble micrometer-sized BiOI precipitates.The activation energies of elemental releases based on dissolution and diffusion-controlled mechanisms are determined with significantly higher energy barriers for dissolution from the composite versus that of the monolithic Cs_(3)Bi_(2)I_(9).The ceramic-based composite waste forms exhibit excellent chemical durabilities and waste loadings,commensurate with the state-of-the-art glass-bonded perovskite composites for I and Cs immobilization.展开更多
文摘Rare earth(RE)-containing crystals have been investigated as media for the immobilization of RE fission products from nuclear waste streams.During reprocessing of spent nuclear fuel,fission products including REs,alkalis,and alkaline earths released from the fuel.One viable option to immobilize the RE fission products is to incorporate them into chemically durable crystalline phases in specific waste forms.This study summarizes the crystal structures and synthesis methods of six RE-containing compounds that have applications in remediation of RE fission products.These compounds include oxyapatite(AE_(2)RE_(8)(SiO_(4))_(6)O_(2)),oxychloride(REOCl),borosilicate(RE_(3)BSi_(2)O_(10)),pyrochlore(RE_(2)M_(2)O_(7)),monazite(REPO_(4)),and perovskite(REMO_(3))where AE denotes alkaline earth metals and M denotes transition metals.This review provides an overview of literature on the usage of these six compounds for immobilizing RE fission products and summarizes different synthesis methods for producing these compounds.Comparisons of structural parameters with different REs in each compound are also discussed.
基金supported as part of the Center for Performance and Design of Nuclear Waste Forms and Containers(WastePD),an Energy Frontier Research Center(EFRC)funded by the U.S.Department of Energy,Office of Science,Basic Energy Sciences under Award DE-SC0016584。
文摘Perovskite-based ceramic composites were developed as potential waste form materials for immobilizing cesium(Cs)and iodine(I)with high waste loadings and chemical durability.The perovskite Cs_(3)Bi_(2)I_(9)has high Cs(22 wt%)and I(58 wt%)content,and thus can be used as a potential host phase to immobilize these critical radionuclides.In this work,the perovskite Cs_(3)Bi_(2)I_(9)phase was synthesized by a cost effective solution-based approach,and was embedded into a highly durable hydroxyapatite matrix by spark plasma sintering to form dense ceramic composite waste forms.The chemical durabilities of the monolithic Cs_(3)Bi_(2)I_(9)and Cs_(3)Bi_(2)I_(9)-hydroxyapatite composite pellets were investigated by static and semi-dynamic leaching tests,respectively.Cs and I are incongruently released from the matrix for both pure Cs_(3)Bi_(2)I_(9)and composite structures.The normalized Cs release rate is faster than that of I,which can be explained by the difference in the strengths between Cs-I and Bi-I bonds as well as the formation of insoluble micrometer-sized BiOI precipitates.The activation energies of elemental releases based on dissolution and diffusion-controlled mechanisms are determined with significantly higher energy barriers for dissolution from the composite versus that of the monolithic Cs_(3)Bi_(2)I_(9).The ceramic-based composite waste forms exhibit excellent chemical durabilities and waste loadings,commensurate with the state-of-the-art glass-bonded perovskite composites for I and Cs immobilization.
