Reprocessing Nuclear Fuel: A Sustainable Solution for the Future

The operation of nuclear reactors to generate electricity produces a limited amount of Spent Nuclear Fuel (SNF), whose radiotoxicity for a long time, and complex management hampers the future exploitation of such an energy source. However, SNF could be considered as either only waste or as still valuable material, and this opens the door to different possible scenarios for the Nuclear Fuel Cycle. Currently, different approaches are followed worldwide concerning the management of spent nuclear fuel.

Open fuel cycle: disposal into deep underground repositories

In the Open Cycle approach, the fuel is used once and sent to direct disposal without further reprocessing. In this case, the waste has a significant volume, contains 96% of reusable materials and remains hazardous for a long time. Nowadays, several Countries have decided to keep SNF in interim storage instead of final disposal, to postpone the final decision of adopting the reprocessing or direct disposal option. This approach is called Wait and See. In this case, SNF could be stored at the reactor sites or in dedicated storage facilities in dry or wet storage conditions.

Closed fuel cycle: reprocessing for a sustainable future

The Closed Fuel Cycle offers a more sustainable and fruitful option. In this case, after a proper cooling period (about 5 years) in pools at the reactor site, spent nuclear fuel is reprocessed to separate uranium and plutonium from the remaining fission products. This step is achieved by the PUREX (Plutonium Uranium Reduction EXtraction) process, the only commercially available technology. It is applied in reprocessing plants in some Countries such as France, China, India, Russia and Japan. Uranium and plutonium can then be used to produce new fuel, both uranium oxide or mixed uranium and plutonium oxide. This approach enables us to reduce the overall waste volume, as well as better exploit the extracted natural uranium, reducing its extraction and the impact on the environment. Furthermore, after irradiation spent nuclear fuel is highly radiotoxic and can remain dangerous for hundreds of thousands of years. However, reprocessing the spent fuel can cut down the time needed to reach the radiotoxicity of uranium ore to 10,000 years. A good result, but not yet enough.

To definitively boost nuclear energy towards sustainability, researchers are developing additional chemical processes aiming at separating long-lived radionuclides, such as Minor Actinides (Americium-241), from SNF. Once separated and properly added to nuclear fuel, they could be transformed into shorter-lived or stable elements through nuclear reactions in suitable new nuclear reactors. This strategy is called Partitioning & Transmutation (P&T) and enables us to further reduce the overall radiotoxicity of the final nuclear waste. Indeed, while in the case an open cycle option is chosen, SNF radiotoxicity reaches the level of natural uranium in around 300,000 years. After the removal of U, Pu and Minor Actinoids by P&T approach, it requires only 300 years, a time frame manageable by humankind.

Over the years, significant efforts have been devoted to developing advanced partitioning processes, and although they are not yet available at commercial scale, some have reached a promising technological readiness level.

By applying the P&T strategy, we can greatly reduce the long-term threat of radioactive waste, since less stringent requirements have to be fulfilled by the geological repositories, thus simplifying and making safer nuclear waste storage.