WASTE MANAGEMENT | DU AND HYDROGEN A store of value?
The use of hydrogen as an energy vector could be enhanced by using depleted uranium as a hydrogen storage medium. The UK recently granted research funds to explore this option
URANIUM’S CHEMICAL INTERACTION WITH HYDROGEN represents both a threat and an opportunity. At room temperature uranium, in common with other metals, tends to absorb hydrogen to form a stable metal hydride, UH3
. In a waste context, uranium hydride is cited as a Janet Wood
Expert author on energy issues
hazard during storage and handling of uranium metal. According to a report produced for UK body Radioactive Waste Management (RWM) this is because of its potentially pyrophoric behaviour and the risk of fire. The report says bulk accumulations of uranium hydride can exhibit a highly exothermic oxidation reaction on exposure to water or water vapour with atmospheric oxygen. The reaction with atmospheric oxygen is characterised at its most reactive extreme by high temperatures, red-hot glow, and some particulate release. A number of events may have been connected to ignition
of wastes containing uranium as a result of uranium hydride formation during storage and “these observations, and confusion about where and when uranium hydride could form and how it could react, have historically led to a highly conservative approach to the design of treatment, storage and handling processes for metallic uranium fuel and associated wastes”. The caution appears to be abating: the report also says
significant progress has been made in understanding the formation and properties of uranium hydride under fuel and waste storage conditions in recent years and it now seems there may be either little reaction on exposing uranium hydride to atmospheric oxygen, or a delayed reaction.
On the side of opportunity, the fact that depleted uranium can absorb hydrogen atoms and, when heated,
then release them means it can potentially be used as a storage medium. It is already used in this way for tritium, one of the hydrogen isotopes that will be required to fuel fusion reactors. Swiss company Tritec offers depleted uranium ‘beds’ for tritium handling on a small scale as a commercial product. The range of sealed ‘beds’ with one or two valves for tritium input and extraction have from 1g to 30g of depleted uranium in products up to 20cm long, and the total capacity of the largest is 10 kCi. Depleted uranium has also been chosen as the solution
for storing tritium at the next generation fusion test reactor, ITER, in preference to other metals with similar hydrogen absorption properties. ITER says depleted uranium (U-238) has the most suitable physicochemical properties. This experience of storing tritium has sparked interest in
uranium as a storage medium in the context of the growing need for hydrogen as an energy vector to complement electricity in a decarbonised energy system. There is already a significant and direct need for hydrogen in producing steel or chemicals, but it is also expected to be an important energy vector in its own right in fuelling industrial heat or heavy transport, as well as in generating power using relatively familiar gas turbines adapted to be fuelled by hydrogen instead of natural gas.
On-site storage Meanwhile, the global hunt is on for new forms of long duration storage to absorb renewable (and nuclear) power generated at times of excess supply and retain it – for months or seasons – for use at times when low-carbon power supplies fall short of demand.
Right: The Culham Science Centre will be home to the HyDUS hydrogen storage initiative
Far right: Could depleted uranium become a valuable resource for the hydrogen economy?
34 | March 2023 |
www.neimagazine.com
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