HYDUS - Off-peak Energy Storage from Nuclear Power Stations Using Repurposed Nuclear Waste - 24352

Natural gas is an effective fuel because it can be easily stored, transmitted via pipelines, and combusted for heat and the electricity generation. However, to achieve net zero carbon emissions, the utilization of natural gas (methane) must cease. Using the coordinated development of nuclear energy and renewables will be challenging without an additional energy source that provides flexibility, storage capability, and responsiveness to adapt to rapidly changing energy grid demands. Hydrogen is a highly combustible gas that has the potential to replace methane. Most importantly, hydrogen gas is relatively easier to produce, either from water using electrolysis or from methane using steam reformation. However, the safe storage of hydrogen is more challenging than methane, and without efficient storage, it simply won’t achieve its potential to substitute the natural gas. Physical storage of hydrogen is considered challenging and inefficient. Storing hydrogen as a compressed gas at pressures up to 900 times atmospheric is volumetrically inefficient and carries safety implications, whilst storing it as a liquid requires costly and constant cooling to cryogenic temperatures.
Depleted uranium (DU) emerges as a promising alternative to such limitations of existing hydrogen storage methods. i. Many different metallic elements in the periodic table, will react with hydrogen to form a chemical compound known as a hydride (or metal hydride). From a chemical perspective, the ‘king’ of the hydride-forming metals is Palladium, that offers the highest hydrogen storage volumetric capacity. However, this material is simply too expensive and scarce to be used in a large-scale bulk hydrogen storage solution. DU is the second most volumetrically efficient hydride-forming metal after palladium. The UK has accumulated a substantial amount of DU over several decades through the uranium enrichment process used in the production of nuclear fuel and there is currently limited commercial application for this stockpile.

The DU stores hydrogen in the form of Uranium trihydride (UH3) which contains three hydrogen atoms for every uranium atom. This compound can chemically store hydrogen at ambient pressure and temperature at more than twice the density of pure liquid hydrogen for the same volume. To release the hydrogen from the hydride, all you do is heat it. (The metal hydride is heated to release the hydrogen). At temperatures above 250°C the hydride starts to thermally decompose, releasing hydrogen as a gas and leaving the uranium as a metal again. The reversible nature of this reaction allows the hydride to be formed and unformed repeatedly, enabling its use as a high-density hydrogen storage material which is already available in large quantities due to its stockpiling as a ‘waste’ by-product.

Whilst the tritium storage credentials of uranium have been rigorously proven at the laboratory scale and at the fusion demonstrator JET for over 30 years, there is a need to prove the concept and effectiveness of DU hydrogen storage (HyDUS) at larger scales for improving the flexibility of the national power and energy grids. This is exactly the purpose of the HyDUS project, a collaborative venture involving EDF as the interested energy vendor, Urenco as the owner of the waste DU, and the University of Bristol with the UKAEA as the architects of the technology. The team will embark on building and proving the world’s first pilot scale demonstrator of bulk chemical hydrogen storage using DU.

Within 18 months the team will attempt to prove both the technical and commercial viability of this technology as a longer duration energy storage solution for the UK. The HyDUS project aims to transform DU from a mere by-product to a wonder-material illustrating the possibility of adopting sustainable practices to unlock the potential value trapped within the nuclear waste materials.