GREENCDT The electrochemistry of silver and its application in the dissolution of spent nuclear fuel

Supervisors

1. Professor Colin Boxall, email: [Email Address Removed]
2. Dr Fabrice Andrieux, email: [Email Address Removed]
3. Dr Chris Maher (The National Nuclear Laboratory)

To maximise the benefits of near-zero carbon nuclear energy, closed nuclear fuel cycles may need to be implemented in the UK or elsewhere later this century. Closed fuel cycles are those in which actinides are recovered from used nuclear fuel for recycling into new fuels for advanced reactors. In the UK, this recovery was effected by the PUREX (Plutonium-Urananium Redox EXtraction) process. This involves several stages:

1. The headend stage, involving the dissolution of the spent fuel in nitric acid; and
2. The separations stage where the actinides are separated from the acid solution by solvent extraction.
3. The finishing stage where the separated actinides are converted to pure U and Pu products.

Closed cycles offer the potential advantages of minimising high level wastes and maximising use of natural uranium resources. The UK is seeking to develop advanced fuel cycles that offer further advantages in separation processes with enhanced standards in economics, safety, proliferation resistance, sustainability and flexibility. This has led to the concept of an “Advanced PUREX” process that can produce a mixed (U,Pu) and a pure U product by recycling either conventional uranium oxide-based fuels – albeit operated to higher uranium usage or “burnup” – and/or new uranium/plutonium mixed oxide (MOX) fuels to.

However, a key issue in the dissolution of used high plutonium content fuels – such as high burnup UO2 and MOX based fuels – is the presence of insoluble plutonium rich particles that require more aggressive dissolution methods at the headend stage than those offered by nitric acid alone. One such method involves the use of powerful oxidising agents such as silver(II) to oxidatively dissolve the Pu-rich regions of the fuel.

This project, a collaboration with the UK’s National Nuclear Laboratory (NNL), will provide experimental evidence to support such a fuel dissolution process, with the main focii being on understanding how oxidising species such silver(II) or ozone dissolve fuel, and how this may be impacted upon by the presence of insoluble fission products (e.g. Ru, Pd, Pt, Rh, Mo) as potential interferrants in the oxidative dissolution process. Using new, advanced simulants for real fuels (so-called SIMFUELs), experimental work will be conducted primarily in Lancaster’s UTGARD (Uranium-Thorium beta-Gamma Active R&D) Lab, with results informing and complementing studies on real spent fuel conducted at NNL’s Central Laboratory.