Step-by-step challenge of debris characterization for the decommissioning of Fukushima-Daiichi Nuclear Power Station (FDNPS)

The key role of sample analysis in Fukushima Dai-Ichi decommissioning, debris management, and accident progression investigation

“…Among the variety of materials formed at 1F, fuel-containing samples can be considered a basic source of information for both accident analysis and debris removal. This review summarizes previously published analysis results with a particular focus on the U-containing samples, most of which were published as reports and presentations in Japanese and in the following reviews: Grambow et al (2021), Barrachin et al (2022), and Kurata et al (2022). Based on the data obtained from the various Frontiers in Nuclear Engineering frontiersin.org investigations of the three severely damaged units, TEPCO and JAEA collaboratively developed and kept updating a core status map that reflects up-to-date hypothesis on fuel debris distribution (fdada.info, 2023).…”

“…Regarding the internal investigation, since the radiation dose around the X-6 penetration was relatively low, direct access to the inside of the RPV pedestal was planned. At the beginning of 2017, IRID performed the first investigation using a pan-tilt camera attached to the head of a long pole (Kurata et al, 2022). A large hole was observed in the grating of a work platform, which was located in the center of the RPV pedestal.…”

“…Furthermore, small amounts of deposits were detected adhering to the CRD housing attached to the RPV lower head. This could suggest that a small failure also existed at the RPV lower head (Kurata et al, 2022).…”

“…Several segments of severely damaged structural steel materials were observed to have penetrated into the debris body. In addition, a small mountain-like accumulation was observed in the center-top region of the debris pile, suggesting that the fuel debris may have been rather viscous during relocation (Kurata et al, 2022).…”

Chemical species of cesium and iodine in condensed vaporized microparticles formed by melting nuclear fuel components with concrete materials

“…Analyses of the FNPP accident [41][42][43][44][45][46][47] focused on the components of the fuels, stainless steel, and control blades but not on the condensed vaporized materials. Simulation analysis revealed that the chemical species of Cs and I generated during the severe accident was CsI, which may transform to CsOH in the presence of steam in a container vessel.…”