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A primary target towards the clean-up operation of the Fukushima disaster is the retrieval of Molten Core-Concrete Interaction (MCCI) products, presently residing on the basement of the damaged nuclear reactor Units 1–3. MCCI is a fusion of materials, composed of both nuclear fuel cladding and neighbouring structural components. Determining the currently unknown, physical and mechanical properties of MCCI is essential for successful and timely retrieval. In this paper, we aim to experimentally quantify the mechanical properties of a material fabricated to resemble MCCI. A small-scale representative specimen was mechanically tested using Hertzian indentation stepwise loading. Synchrotron X-ray computed tomography was conducted at several loading stages to reveal the sample microstructure and mechanical degradation. The acquired tomograms were analysed by digital volume correlation to measure full-field displacements and strains developed within the sample volume. Young’s modulus and Poisson ratio were determined via this combined methodology.

To reflect potential conditions in a geological disposal facility, uranium was encapsulated in grout and submersed in de-ionised water for time periods between 2-47 weeks. Synchrotron X-ray Powder Diffraction and X-ray Tomography were used to identify the dominant corrosion products and measure their dimensions. Uranium dioxide was observed as the dominant corrosion product and time dependent thickness measurements were used to calculate oxidation rates. The effectiveness of physical and chemical grout properties to uranium corrosion and mobilisation is discussed and Inductively Coupled Plasma Mass Spectrometry was used to measure 238U(aq) content in the residual water of several samples., Supplementary raw data to the article described above.

International audience; Synchrotron X-rays have been used to study the oxidation of uranium and uranium hydride when encapsulated in grout and stored in de-ionised water for 10 months. Periodic synchrotron X-ray tomography and X-ray powder diffraction have allowed measurement and identification of the arising corrosion products and the rates of corrosion. The oxidation rates of the uranium metal and uranium hydride were slower than empirically derived rates previously reported for each reactant in an anoxic water system, but without encapsulation in grout. This was attributed to the grout acting as a physical barrier limiting the access of oxidising species to the uranium surface. Uranium hydride was observed to persist throughout the 10 month storage period and industrial consequences of this observed persistence are discussed