Tritium-extracting solution decontaminates nuclear waste
EU-funded researchers have been recognised for their ground-breaking work on recovering and reusing waste material in nuclear fusion reactors. They developed and demonstrated new membrane technologies capable of decontaminating waste and extracting valuable tritium for re-use.
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The research team from the Italian agency ENEA and French agency CEA working in the framework of the EFDA (now EUROfusion) programme won Second Prize at the international 2016 Symposium on Fusion Technology (SOFT) for their achievements.
Recycling at nuclear plants
In nature, hydrogen comes in three forms called isotopes. Deuterium is twice as heavier as common hydrogen, and tritium three times heavier.
First generation fusion machines burn the hydrogen isotopes deuterium and tritium as fuel, explains ENEAs Silvano Tosti, who worked on the project. Tritium, which is radioactive, must be handled carefully and any by-products must be disposed of as radioactive waste.
Tosti and the team of ENEA and CEA researchers developed a process and constructed a new type of palladium (Pd) silver (Ag) alloy membrane reactor. It is able to effectively recover tritium from waste streams, which can then be re-used.
The process is also of huge interest to conventional nuclear facilities because tritium is an extremely expensive material, costing around USD 30 000 (€ 27 340) a gram as it is practically non-existent in a natural state. The membranes are permeable for hydrogen isotopes, but not for other gas molecules and are thus able to separate tritium. Reducing the tritium content of waste is also important because disposal costs depend on the level of contamination.
We were also able to show that the radioactivity of the tritiated waste is reduced to such an extent that it can be stored under less severe conditions, says Tosti. This will help to reduce waste management costs. Compared to alternative systems, the membranes in our new device are more stable and the overall process is more energy efficient.
Following completion of this work, both ENEA and CEA filed two patents, which have since been granted by the European Patent Office. One is related to the process, while the other is related to the membrane reactor.
Further research potential
The technology was developed to deal with waste at the Joint European Torus (JET), a pan-European fusion research facility in the UK that is investigating the potential of fusion power as a safe, clean, and virtually limitless energy source for future generations. JET is the only operational fusion experiment capable of producing fusion energy.
ENEA has since gone on to sell three Pd-membrane devices and received numerous calls of interest from European research institutes. Tosti believes that the membrane technology has significant potential for use in future fusion machines and reactors, due to be developed as part of the international ITER and DEMO projects.
This innovation may offer new applications in hydrogen technologies and the future hydrogen economy.
Another important characteristic of the technology we developed is its applicability to the production of ultra-pure hydrogen, says Tosti. For instance, hydrogen produced by membrane reactors can be sent to PEM fuel cells where electricity is produced. This technique was used to power the electric engine of a tractor. Another project has demonstrated that hydrogen produced by these membrane systems can significantly increase the efficiency of cogeneration systems consisting of fuel cells.
Tosti says that both ENEA and CEA now intend to use the SOFT PRIZE award money to further develop thin-walled Pd-tubes used in the membrane reactors. If all JETs waste inventory were to be treated, the membrane reactor prototype would need to be scaled up to a multi-tube version, he says. New connections have already been developed by ENEA, and a patent filed. A membrane reactor using new Pd-tubes and connections will be soon tested by CEA laboratories.
The SOFT Innovation Prize honours excellent ideas and developments in fusion research and is awarded at the Symposium on Fusion Technology (SOFT). The main criteria are originality, outstanding achievements, economic relevance, and prospects of success. The SOFT Innovation Prize is supported by the Horizon2020 Euratom Research and Training Programme 2014 2018.