Ten years after the nuclear accident in Fukushima, studies to understand the causes and consequences of the nuclear disaster continue. After the accident, the three reactor cores melted, producing several hundred tonnes of corium and fuel debris, continuously generating heat through the radioactive decay of the fission products present in the corium.
Coordinated by Subatech, a collaboration with JAIEA, Kyshu University and Tokyo University of Technology in Japan and the French Atomic Energy Commission (CEA) has been initiated to summarise the research of the ten years after the accident.
These studies are crucial for any planning of reactor decommissioning.
The temporal evolution of water chemistry and radionuclide inventories leached from the debris by the cooling water was studied. A comparison between the concentration ratios of actinides and fission products measured in water and the results of leaching studies of spent nuclear fuel or debris simulated in the laboratory was carried out.
As with the leaching of spent fuel in the laboratory, the fractions of the 134,137Cs inventories that are analysed in the cooling water are orders of magnitude larger than those of the actinides. After more than 10 years of contact between fuel debris and water, the release rates of 137Cs remain higher than those of actinides even though the release rate of 137Cs from the debris has decreased by a factor of about 100 during this period. Actinide fixation in the debris is strong. The high stability of actinide fixation in debris makes the option of direct disposal of fuel debris as waste in appropriate containers after the decommissioning of reactors in the future viable.
Access to the article "Ten years after the NPP accident at Fukushima : review on fuel debris behavior in contact with water, Journal of Nuclear Science and Technology", https://doi.org/10.1080/00223131.2021.1966347
Authors : Bernd Grambow, Ayako Nitta, Atsuhiro Shibata, Yoshikazu Koma, Satoshi Utsunomiya, Ryu Takami, Kazuki Fueda, Toshihiko Ohnuki, Christophe Jegou, Hugo Laffolley& Christophe Journeau (2021)
Status of reactor corres, Fukushima at 2018: a) unit 1; b) unit 2, c) unit 3. In blue: as the cooling water flowed, the cores largely melted and much of it fell onto the concrete at the bottom, references: Mizokami S, Rempe JL. The Events at Fukushima Daiichi. Reference Module in Earth Systems and Environmental Sciences . Elsevier; 2020.