Reactor design to make nuclear waste less radioactive
High-level nuclear waste includes long-lived and high-radiotoxic radionuclides. An EU-funded project helps to solve this issue by carrying out the research needed to build a facility that is capable of splitting material with long radioactive half-lives into radionuclide products with 1 000 times shorter half-lives.
© Vlad #193947515, source: stock.adobe.com 2019
High-level nuclear waste remains hazardous for very long periods. Could it be made safer before being buried underground? Work by SCKCEN and its international partners is aiming to do just that, in support of the realisation of the MYRRHA research facility in Belgium.
Here, a reactor is going to be built not to generate electricity but to dramatically reduce the radiotoxicity of high-level nuclear waste from spent fuel via nuclear transmutation.
The EU-funded MYRTE project is carrying out research towards demonstrating the feasibility of transmuting high-level waste at industrial scale. The idea is that radiotoxic atoms with long half-lives are each split into two much less hazardous products with strongly reduced (by 1 000 times) half-lives, in a novel reactor system using nuclear fission.
If there were technical means to reduce radiotoxicity from hundreds of thousands of years to some hundreds of years, that would be a major breakthrough for the public accepting a solution to the nuclear waste challenge, says project coordinator Peter Baeten of the SCKCEN Belgian Nuclear Research Centre. It would be more manageable compared to a human life timescale.
The waste would still need deep underground storage, but the high-radiotoxic radionuclides products would not last as long, the heat load would be easier to manage and the footprint of the underground disposal site would be reduced.
To achieve its goal, the demonstration MYRRHA research facility needs to have a combination of innovative elements. MYRTE is helping to realise these through work packages focusing on the accelerator, thermal hydraulics, chemistry, reactor physics and fuel.
MYRRHA is an accelerator-driven system, comprising a proton accelerator coupled to a sub-critical reactor. The reactor therefore only works when the accelerator injects protons into it. MYRTE has made advances in the design of the accelerator and the safety demonstration of the reactor concept.
One of the main challenges is optimising the reliability of the accelerator, says Baeten. The project is constructing the first part of this unique accelerator. This has also had an impact on the accelerator community, as now they see, thanks to this project, that major steps can be made in improving reliability. This is an important spin-off and valorisation of the project.
Thermal hydraulics studies are providing a better understanding of the behaviour of the special coolant, liquid lead-bismuth, inside the reactor. The chemistry work package has taken major strides in completing the studies required by the safety authorities for assessing the behaviour of radioactive elements produced in the reactor.
The behaviour of neutrons, the sub-atomic particle flying around the sub-critical core, is studied in a 100-watt reactor. They behave the same way as they do in a 100-megawatt reactor. We have built a special research facility to study them, we call it mini-MYRRHA, says Baeten.
The final work package concerns dedicated transmutation fuel. Specific elements, called minor actinides, must be removed from the spent fuel from nuclear power plants, then converted into fuel targets to put in the accelerator-driven system.
The advantage of doing transmutation in an accelerator-driven system is that you can do it in a concentrated way, says Baeten. It means you can put between 40 and 50 % of the high-level waste into your reactor core. Without this accelerator and a sub-critical system, you can only put in around 2-3 % in reactors intended for electricity production.
Whether or not EU countries will continue to use nuclear for electricity production, governments are still confronted with the challenge of high-level nuclear waste. It is an issue for every country that has or once had a nuclear power programme.
The big advantage of this European project is that you can call on the excellence of European partners. This is a big added value, because here in Europe we have several centres of excellence in different technical domains, Baeten says.
For example, he notes the strong collaboration between French and German partners in building the accelerator, and the role of Swiss expertise in the chemistry work package.