AGR, Magnox and Exotic Spent Fuels

The UK’s used nuclear fuel is currently reprocessed at THORP (Thermal Oxide Reprocessing Plant)  at Sellafield. This is scheduled to close within 5 years. Future arisings will be sent to a GDF (geological disposal facility) although this is not due to open until around 2075. Between THORP closing and the GDF opening, UK used fuel will be held in interim wet storage in ponds at Sellafield. Current storage periods are typically less than 10 years, although this may extend to as long as 100 years after THORP closes. Fuel cladding (a steel sheath encasing the uranium dioxide fuel pellets) can be breached due to corrosion or damaged during dismantling. Evolution of both the steel cladding & the uranium dioxide surfaces upon consequent exposure to pond water can be considered as corrosion processes and so conveniently studied by electrochemical methods.

Using novel fuel simulants (SIMFUELs), we have conducted preliminary electrochemical studies on coupled SIMFUEL-steel samples in pond buffer and found that they may interact in a manner that might promote uranium dioxide corrosion. This suggests that both cladding and pellets of UK used fuel are corroding during wet storage. Therefore, we propose to study the corrosion behaviour of uranium dioxide, SIMFUELs and steel cladding in pondwater simulant. In the first instance, voltammetry and impedance spectroscopy studies will be conducted on separate UO2, SIMFUEL and steel cladding samples as a function of water composition, temperature and hydrogen peroxide concentration (the latter to mimic radiolysis of water).