EFFECTIVE/RAPID IMMOBILIZATION OF RADIONUCLIDES FROM FUKUSHIMA DECOMMISSIONING BY SPARK PLASMA SINTERING PROCESS

Abstract

The immobilization of the radionuclides produced in the decommissioning of Fukushima Daiichi nuclear power plant (1F) is a growing priority for waste management. Here, we have investigated the effect of spark plasma sintering (SPS) on the solidification process of wasteform mainly for Fukushima decommissioning to add more insight into this field. To develop the solidification process for wasteform, simulated ALPS precipitation waste was solidified. SPS technique successfully increased the density of ALPS phosphate significantly at 600 °C, and the value was three times higher than that of the normal heating sample; succeeded in significant volume reduction to 1/3. Crystallization to phosphate-type crystalline occurred at 600 °C by SPS, and this is likely the reason why significant densification occurred. Above results leads to suppression of volatile substances because of low sintering temperature and high-speed solidification process by SPS. Surprisingly, in leaching test for ALPS phosphate, the leaching of Ca, Mg, Fe and Cs was greatly suppressed by solidifying by SPS. Additionally, we demonstrated first the fabrication of hybrid waste containing ALPS phosphate powder as primary waste by encapsulating it in matrix material using SPS, which is expected to improve the safety and reliability of wasteform. Solidification of hybrid waste with several matrix materials could be achieved, and ALPS phosphate powder was stably maintained in matrix.