Hydrogen Bubble Growth and Release Dynamics in Glass Bead Beds for Applications in Legacy Nuclear Waste – 24256

Abstract

For the planning and design of long-term storage facilities and the monitoring of interim waste storage, a thorough comprehension of the gaseous release is required. A build-up of gases such as hydrogen, underscores the importance of studying these dynamics for interim and geological disposal facility (GDF) safety cases. The UK Radioactive Waste Management (RWM) organization estimates around 103 000 tons of metals that are categorized as GDF waste. The volume of hydrogen gas from radiolysis and/or corrosion that is trapped in interim waste storage facilities is unknown. This uncertainty and continuous gas release needs to be considered in the design of containers for radioactive waste storage. Gas transport occurs via capillary invasion or sediment fracturing. Bubbles in sediments with low yield stress may fail to invade or fracture these sediments resulting in gas build-up. Over-estimation of hydrogen hold-up per waste material will result in high mobilization and storage costs hence the need for a greater understanding of bubble dynamics and sediment mechanics. This work uses silica glass beads to simulate characteristics of granular nuclear waste. Hydrogen is generated from induced magnesium corrosion in columns packed with glass beads. Sodium chloride was added to catalyze corrosion by disturbing the protective magnesium hydroxide layer that forms in room temperature water. Four sizes of glass beads 88 µm, 203 µm, 394 µm and 555 µm were used to see the effects of particle size and yield stress on hydrogen generation rates, bubble sizes and overall release versus retention rates. Hydrogen retention and bed expansion were found to increase with decreasing particle size. Smaller particles had higher total hydrogen yield except for the 88 µm which had large gas pockets. Gas transport by invasion increased with increasing particle sizes which had higher yield stress values. Samples are imaged using high resolution X-ray Computed Tomography to study the microstructure and bubble distribution. A sample of hydrogen bubbles in glass beads of mean size 203 µm, was imaged with a pixel size of 53 µm and showed coalescence of bubbles at the edges of the sample from the wall effects. The contribution from micro and macro bubble pores will be evaluated after selecting an effective region of interest (ROI) and a gas network model will be developed from this. Over time, the glass beads show plasticity after bubble formation like other granular materials such as sand, which tend to have spherical bubbles. This project is in partnership with Sellafield Ltd