Crystalline phosphates for HLW immobilization - composition, structure, properties and production of ceramics. Spark Plasma Sintering as a promising sintering technology

Abstract Available publications on crystalline materials used to immobilize HLW and actinides have been analyzed. Select compounds and solid solutions covered in this paper are phosphates of the following structural families: monazite, xenotime, kosnarite (NZP),apatite and britholite, langbeinite, whitlockite and thorium phosphate diphosphate (TPD). These materials have been shown to be fit for “nature-like” disposal (except TPD), they have a wide spectrum of isomorphic substitutions of cations and/or anions, and high heat, chemical, and irradiation stability. They can be also used in geoenvironmental engineering. The studies taken into consideration follow the materials science approach that rests on the “composition – structure – synthesis – property” basis. The analyzed papers describe materials synthesized using Spark Plasma Sintering, a process that results in rapid formation of virtually poreless ceramics and improves environmental safety both at stage of HLW immobilization and during long-term storage.