Immobilization of strontium, cesium and rhenium into α-SiAlON ceramics assisted with co-doping of yttrium

Abstract

Immobilization of long-lived fission products (LLFP) such as radioactive Tc, Cs and Sr into α-SiAlON ceramics was evaluated using stable isotopes instead of radioactive isotopes, and the applicability of α-SiAlON ceramics as the inert matrix for transmutation of LLFP was investigated. In the case of single addition of SrO, SrCO₃, Cs₂CO₃ or ReO₂ to the starting materials, α-SiAlON single phase was not formed after hot-pressing. When Y₂O₃ was added with SrO, SrCO₃ or Cs₂CO₃ to the starting materials (α-Si₃N₄, AlN and α-Al₂O₃) in optimum compositions, α-SiAlON single phase was obtained after hot-pressing at 1700°C or 1800°C. From the EDS analysis, Sr and Y were detected from grains. It is suggested that Y would assist the expansion of interstices of α-SiAlON lattice, resulting in the incorporation of Sr²⁺ into α-SiAlON lattice. In the case of Cs addition with Y, Cs was not incorporated into interstices due to much larger ionic radius of Cs⁺. Bulk density of hot-pressed α-SiAlON ceramics obtained in this study was higher values and densification proceeded well. From these results, it was found that the immobilization of Sr in α-SiAlON was successfully achieved with co-doping of Y, and α-SiAlON ceramics would be an inert matrix for transmutation of long-lived radioactive Sr.