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

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 1700degC or 1800degC. 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. (author)