Speaker
Description
It has now been 15 years since the Fukushima Daiichi nuclear power plant accident, and we are still working toward our mission of achieving safe decommissioning, which is expected to require approximately 40 years. One of the most difficult challenges is the presence of approximately 880 tons of nuclear fuel debris in the reactors that melted during the accident. Key questions include: (1) how can the debris be safely removed, (2) how can nuclear fuel be separated from alpha-contaminated waste within the debris, and (3) how can long-term storage of the debris be managed? The answers depend strongly on the actual composition of the debris.
Japan Atomic Energy Agency (JAEA) has successfully obtained two debris samples, which were transported to the JAEA Tokai campus in November 2024 and April 2025. From isotopic and elemental analyses using ICP-MS and SEM, the majority of components, such as uranium and iron, have been identified. However, trace components (<1%), including 243Am, 243Cm, 238Pu, 239Pu, and 10B, are difficult to identify due to interfering nuclides, even though these nuclei are critical for controlling criticality and ensuring safe decommissioning.
To analyze such trace components using state-of-the-art nuclear physics and chemistry techniques, we employ (1) Coulomb excitation activation analysis coupled with a Ge detector array and (2) alpha–gamma coincidence measurement techniques. As a validation experiment for method (1), mock debris targets were prepared using electrodeposition techniques and irradiated with a 58Ni beam from the JAEA-Tokai tandem accelerator. Preliminary results will be presented.
Actual debris samples will be provided to us in 2026. We will then perform both alpha–gamma coincidence measurements and Coulomb excitation activation analysis using real debris samples.
| Contribution category | Experiment |
|---|---|
| Presenter status | Faculty/Staff |