Crystalline compounds for remediation of rare-earth fission products: A review

Abstract 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 [AE2RE8(SiO4)6O2], oxychloride [REOCl], borosilicate [RE3BSi2O10], pyrochlore [RE2M2O7], monazite [REPO4], and perovskite [REMO3] 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.