Paola Batistoni is the project leader of the Work Package containing technology experiments related to the upcoming second deuterium-tritium at JET. She explains why these experiments are so important for ITER. But to start with, she gives an overview of “Neutronics” and why studying little particles helps to support the huge tokamak which is currently being built in the south of France.

What is neutronics?
Neutronics is a discipline which studies the complex diffusion of neutrons through matter and their interactions with nuclei. In a DT fusion reaction, a neutron and an alpha particle are produced. The neutron, which carries 80% of the energy produced in the reaction, is not confined within the plasma. It escapes and penetrates into the components surrounding the plasma chamber, mainly the blanket. Here it releases its energy which is then used to produce electricity.

However, neutrons cannot be easily stopped; they are able to penetrate several metres into materials before they come to a standstill. As they move within the materials, they produce gamma rays, secondary particles and radioactive nuclei. They also create microscopic changes in the material structure which may cause degradation of physical and mechanical properties. We, as neutronics experts, support the reactor design with complex analyses, suggesting design configurations and materials that can be used to minimise the escape of neutrons and their negative impact.

Why is the new DT campaign at JET so important?

The JET experiments are designed to reach and investigate ITER-like plasma regimes of operation. However, the project also addresses ITER-relevant technology issues, such as the validation of neutronics codes that are used in ITER. We need these to predict their effect on materials, the occupational dose and the performance of diagnostics exposed to high neutron flux. In the new DT campaign, internally referred to as DTE2, JET will operate with tritium and generate neutron yields large enough to cause easily measured activation in materials and degradation in their physical properties, as well as dose rates in the tokamak environment. By measuring these quantities and comparing them with simulations and numerical predictions, we aim to reduce the risks and uncertainties associated with ITER operation and maintenance.

What will you investigate in particular?

Our aim is for JET to obtain the first complete and consistent “nuclear case” for a tokamak using the deuterium-tritium fuel cycle. This includes the accurate measurement of the neutron source and radiation field in the device and the surrounding areas as well as the effects on materials exposed to 14 MeV neutrons, the tritium inventory in plasma-facing materials, the amount and type of waste produced, and the occupational radiation exposure. I think we are addressing the key aspects of ITER for which we still have limited experience. We are working to obtain the best returns with this new set of experiments.

What are the key aspects for ITER?

Our experiments carried out as part of the current JET project will validate the state of art neutronics codes used in ITER. If you consider the size of ITER and the complexity of its configuration, extensive neutronics calculations are required in order to derive the neutron diffusion (and the diffusion of the secondary radiation they produce) from the plasma chamber through the device, biological shield, and the tokamak building. These calculations must be reliable and validated. We will use them to predict the lifetime of the components, the dose to workers and the amount of radioactive waste produced.

What are the benefits and pitfalls of an international network?

I have always appreciated working within international frameworks with people maintaining different specialisations and complementary competences. Therefore, I have always promoted the widest collaboration possible in all of the projects I have coordinated. In the current project, we benefit from all fusion nuclear technology competencies present in Europe. It would simply not be possible to find all of these competencies in any one single laboratory. Coordinating different people and teams is like conducting an orchestra that frequently performs via video-conferencing. It is not easy to keep everybody fully tuned and synchronised, but we also hold frequent meetings in person. We often gather for experiments and have the opportunity to work together, thus gaining a full common understanding of what we are doing.

To what extent do these experiments support the progress of the European fusion programme?

The JET experiments are devoted to the preparation of ITER, the exploitation of which is a pillar of the European fusion programme. But I would like to add that I am happy that, together with very expert senior scientists, there are many young European scientists and engineers participating in these experiments and analyses. They are gaining unique experiences working with a real fusion device that will certainly be very valuable later i in ITER . I even would like to see more young scientists and engineers, for example, among those who work on the development of DEMO. Participating in one or more stages at JET would help them to better understand the real life situation within a tokamak working with tritium and producing high fusion power.