Optimising spent nuclear fuel storage in Europe

A new review in EPJ N by members of the EURAD consortium explores the parameters involved in choosing safe long-term storage solutions for spent radioactive fuel and recommends best practice for the industry.

As the world moves away from fossil fuels, nuclear power remains a crucial component of our energy mix. Yet there are still relevant questions about improving safety, particularly regarding the safe storage of radioactive waste. The EURAD (European Joint Programme on Radioactive Waste Management) project has been exploring the most appropriate and publicly acceptable solutions to this problem.

Now, a group of EURAD-funded scientists, led by Dimitri Alexandre Rochman of the Paul Scherrer Institut, Villigen, Switzerland, has published an extensive review in the journal EPJ N that addresses a key part of the problem - characterising spent nuclear fuel - and makes recommendations for its safe storage over timescales from years to centuries.

EURAD is a large project involving over 50 collaborating organisations from 20 EU members and three associated states. It has been funded for five years under the EU’s Horizon 2020 programme to study and develop management solutions for all types of radioactive waste.

Spent nuclear fuel (SNF) is fuel that has been used to generate electricity in a nuclear reactor but is no longer able to sustain a thermal reaction due to changes in its isotope composition. It is dangerously radioactive and is classed as ‘high-level’ waste, with the most stringent safe storage requirements.

One of the problems associated with SNF is that we need to improve our knowledge of its exact content (fission products and actinides). “A fuel assembly that has been irradiated in a reactor for a few years contains uranium, plutonium and various other radioactive isotopes, and we want to know their composition better for a safer and more economical handling of such spent fuel; for this, we need to improve the certainty of our estimates,” explains Rochman. “Knowing this is important because we need to set large enough safety margins for all the storage parameters to make sure the storage facility is and remains safe.”

Another parameter that must be considered is heat, which SNF releases in decreasing amounts over time as the spent fuel decays. The casing and other protective layers surrounding the fuel must be designed to minimise any damage from this decay heat, but we need more precise estimates of it.

Rochman and his colleagues predicted nuclide concentrations and decay heat from SNF samples based on measurements and calculations, and compared these values to those obtained from modelling and found in the literature. Then, they combined these to produce estimates for both the values and their uncertainties, modelling decay and cooling for periods of thousands of years. The results were used to recommend best practice for the safe storage of different types of SNF. A conservative approach that takes all remaining uncertainties into account is essential, the researchers suggest.

Some European countries’ nuclear waste management systems are far advanced, while others are just getting started. “Our findings will help these latter countries to take the most appropriate decisions ahead of time, thus preventing the waste of resources,” says Rochman. He expects that the follow-on programme EURAD-2, which begins in 2024, will enable them to fill in current gaps in their research and answer some of the questions that remain.

This "Key Summary" is brought to you in collaboration with SciencePOD.