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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.

How do you characterise the contents of a sealed nuclear waste package without breaking it open? This question is important when the contained corrosion products are potentially reactive with air and radioactive. Synchrotron X-rays have been used to perform micro-scale in-situ observation and characterisation of uranium encapsulated in grout; a simulation for a typical intermediate level waste storage packet. X-ray tomography and X-ray powder diffraction generated both qualitative and quantitative data from a grout-encapsulated uranium sample before, and after, deliberately constrained H2 corrosion. Tomographic reconstructions provided a means of assessing the extent, rates and character of the corrosion reactions by comparing the relative densities between the materials and the volume of reaction products. The oxidation of uranium in grout was found to follow the anoxic U+H2O oxidation regime, and the pore network within the grout was observed to influence the growth of uranium hydride sites across the metal surface. Powder diffraction analysis identified the corrosion products as UO2 and UH3, and permitted measurement of corrosion-induced strain. Together, X-ray tomography and diffraction provide means of accurately determining the types and extent of uranium corrosion occurring, thereby offering a future tool for isolating and studying the reactions occurring in real full-scale waste package systems., (Copyright © 2014 Elsevier B.V. All rights reserved.)

To accurately predict the initiation and evolution of uranium hydride potentially present in nuclear waste containers, studies of simulated conditions are required. Here, for the first time, the uranium-deuterium reaction was examined in-situ, in real time, whilst within grouted media. A deuterium gas control rig and stainless steel-quartz glass reaction cell were configured on a synchrotron beam line to collect X-ray diffraction and X-ray tomography data. It was found that deuteride formation was limited by the uranium and grout thermal conductivities and deuteride initiation only commenced above a threshold temperature. Strong adherence between uranium oxide and grout was also observed. [ABSTRACT FROM AUTHOR]

The present work examines the effect of surface geometry on the reaction between hydrogen gas and uranium metal, forming uranium hydride (UH 3 ), a pyrophoric compound of significance to the civil nuclear industry. Hydride formation was initiated on uranium samples that had been patterned with a focused ion beam instrument to form surface arrays of triangular prisms and pillars with differing apex angles. Post reaction analysis indicated preferential hydride formation at the apex of these features. Additionally, once hydride formation had commenced the observed growth rate on the prisms appeared to accelerate in comparison to the rate exhibited on the surrounding surface. [ABSTRACT FROM AUTHOR]

• Time-resolved investigation of uranium corrosion in Magnox sludge • Corrosion initiates within the first 20 days of sample age • Corrosion morphology suggests the formation of uranium hydride (UH 3) • Migration of corrosion products within the sludge has been observed During the early years of nuclear industry within the UK, the typical route followed to handle Magnox (Mg-Al alloy) casing after separation from the nuclear fuel has been immersion in water temporarily in specifically-designed water ponds. Over the decades of storage, Magnox has been corroding in water, resulting in the formation of sludge within the ponds; known as Corroded Magnox Sludge. Uranium, which has been also contained within the ponds as a result of faults occurring during fuel-casing separation, is susceptible to corrosion in water-rich environments. Under certain circumstances, uranium corrosion products can be highly pyrophoric during oxidation in air. This raises serious concerns regarding the safety margins of nuclear pond decommissioning. The present study attempts to shed light on the behaviour of uranium in a Magnox sludge-surrogate environment, using X-ray computed tomography at distinct time intervals over an 18-month period. Focus was given onto the uranium-sludge interface to determine metallic corrosion onset and evolution. [ABSTRACT FROM AUTHOR]