Spatially resolved isotopic analysis of a uranium-bearing particle from inside the Fukushima Daiichi unit 2 reactor using high-resolution SIMS

Characterizing fuel debris (FD) is critical for decommissioning the Fukushima Daiichi Nuclear Power Station (FDNPS). Samples collected from inside the reactor building through various methods provide valuable insights into the properties of FD. However, localized isotope data from these samples have not been previously reported. In this study, we present the first global report of isotope imaging and ratio data for the FDNPS particle obtained using our novel high-spatial-resolution secondary ion mass spectrometry (SIMS) technique developed for FD analysis. The method successfully mapped the spatial distributions of uranium, a key nuclear fuel component, and boron-10 (10B), a control rod material, within the particle. In addition, the spatial distributions and isotope ratios of B and lithium (Li) in the particles provide definitive evidence that 10B (n, α) 7Li reactions occur in the control rod during normal reactor operation. These findings provide new insights into the FD composition and underscore the effectiveness of SIMS for the detailed characterization of FD.