This review is an up-to-date report of the analysis of U-bearing samples from the Fukushima Daiichi Nuclear Power Station (1F). It summarizes the experience gained after previous severe nuclear accidents in the field of fuel debris analysis and the utilization of the results. Current methods of 1F sample analysis and the main results are presented with a discussion on future strategies of fuel debris analysis and the requirements for 1F decommissioning.

Two crystalline phases, which are analogues of common secondary uranyl minerals, namely, becquerelite (Ca[(UO₂)₆O₄ (OH)₆]·8H₂O) and phurcalite (Ca₂[(UO₂)₃O₂ (PO₄)₂]·7H₂O) were identified on the surface of a Chernobyl corium-containing sample affected by hydrothermal alteration in distilled water at 150 °C for one year. Phases were characterized using Single-Crystal X-ray Diffraction Analysis (SCXRD) as well as optical and scanning electron microscopy. Features of the structural architecture of novel phases, which come from the specific chemical composition of the initial fragment of Chernobyl sample, are reported and discussed. Precise identification of these phases is important for modelling of severe nuclear accidents and their long-term consequences, including expected corium–water interaction processes at three damaged Units of the Nuclear Power Plant Fukushima Daiichi.

Chemical degradation of borosilicate glass doped with ²³⁸Pu was modelled in conditions of a failed underground radwaste repository in granite host rock with bentonite buffer material after penetration of aqueous solutions at temperature of 90 °C. The total duration of the experiment exceeded two years. It is shown that wet bentonite preserved its barrier function and prevents migration of plutonium to the solution. The total amount of plutonium adsorbed on bentonite clay during the experiment did not exceed 0.02% of the initial amount of plutonium in the glass sample. Estimated accumulated dose of self-irradiation of the glass sample after the experiment varies from 3.16 × 10¹⁵ to 3.39 × 10¹⁵ α-decays per gram, which is equivalent to more than 1000 years storage of ²³⁹Pu doped sample with the same Pu content. Beishan granite remained intact, with no evidence of Pu penetration into the granite matrix along mineral grain boundaries.