In-situ immobilization technique for radioactive cesium using laser technology for Fukushima Daiichi decommissioning

Abstract

The decommissioning of the Fukushima Daiichi (1F) nuclear power plant remains a significant environmental concern. A crucial aspect of this process involves the effective immobilization of ¹³⁷Cs to reduce the volume of radioactive waste. This technique traps radioactive materials that adhere to the concrete surface by embedding in the glass, allowing only the glass to be removed during decommissioning. In this study, we first irradiated concrete mixed with ¹³³Cs, which had the same composition as the nuclear reactor building at 1F, using a high-brightness laser beam to immobilize Cs. We then investigated the characteristics of in-situ immobilization of Cs from the aspects of distribution, migration, and elution. X-ray diffraction (XRD) results indicate that the concrete underwent vitrification. Measurements from an electron probe microanalyzer (EPMA) show that Cs exhibits aggregate-dependent heterogeneity within the fused, glass-like concrete. The experimental migration rate of 99 % is more reliable compared to the 57 % achieved through conventional thermal plasma melting of simulated low-level radioactive waste. As far as elution is concerned, the normalized mass loss of the elements is 0.06 to 0.08 g/m², which is below the 2 g/m² limit set by the American Society for Testing and Materials (ASTM) International. Consequently, laser-assisted in-situ immobilization of Cs has superior potential for supporting the decommissioning of 1F by effectively utilizing the hazardous materials on site.