Metal Better Than Carbon for ITER Fusion Reactor, Award-Winning Study Confirms

IAEA May Fawaz-Huber | Oct. 20, 2016

Sebastian Brezinsek receiving the IAEA’s 2016 Nuclear Fusion Journal Prize from Director General, Yukiya Amano ((Photo: Courtesy NIFS))

Metal, rather than carbon, is better suited as material for the inside wall of tokamaks — the experimental machines designed to harness fusion energy — according to the paper that won the IAEA’s 2016 Nuclear Fusion Journal Prize this week. Using metal in the fusion reactor reduces safety hazards that may result from unwanted chemical reactions involving carbon.

Sebastian Brezinsek, from EUROfusion Consortium, won the prize as lead author of the paper ‘Fuel Retention Studies with the ITER-Like Wall in JET’. He received the prize at the 26th IAEA Fusion Energy Conference in Kyoto, Japan, on Monday. The conference was opened by IAEA Director General Yukiya Amano.

Brezinsek and his co-authors conducted experiments at the Joint European Torus (JET) in the United Kingdom, the world’s largest operating tokamak. The findings have confirmed the hypothesis that the operation of plasma—the fuel in which all particles are ionized and can react to a magnetic field—in a tokamak is compatible with metallic walls. This, in turn, means that the materials to be used for the walls in ITER—the world’s largest future tokamak to demonstrate fusion energy production at industrial scale—will result in a significantly reduced trapping of tritium, a radioactive isotope of hydrogen in the fuel.

Tokamaks have been developed over the last decades to enable controlled fusion reactions in a vacuum vessel containing a magnetic field. Because the temperature needed to make fusion reactions possible is in the order of 100 million degrees Celsius, the wall of the vacuum vessel must be protected from the heat emanating from the plasma. Historically, this was done using heat-resistant carbon materials. Due to safety concerns, the total amount of tritium allowed within the vacuum vessel must be kept below a certain limit – which posed a difficulty when carbon was used.

To overcome this problem, ITER was designed to operate with plasma-facing components made of metallic elements that are less reactive to tritium. A replica of the ITER wall was built at JET to conduct various sets of experiments, including those which have now validated the choice of the plasma-facing materials made for ITER.

The experiments conducted by Brezinsek and his colleagues confirmed the use of beryllium and tungsten as plasma-facing materials for the nuclear operation phase of the ITER device.

“The experiment shows that tritium trapping is very much reduced with a beryllium wall,” said Bastiaan J. Braams, Unit Head of Atomic and Molecular Data at the IAEA. “It supports the choice of beryllium for the ITER wall.”

Nuclear fusion, the process that powers the sun, has the potential to provide a virtually unlimited supply of clean, carbon-free energy. ITER’s goal is to allow scientists to study plasmas under conditions similar to those expected in a future fusion power plant. It is planned to produce 500 MW of fusion power.

“This work provides great confidence in the choice of plasma-facing materials made for ITER,” said Richard Kamendje, a nuclear fusion physicist at the IAEA. “It is a good indication that ITER will be able to fulfil regulatory requirements for fuel retention, which impose a limit on the amount of tritium inventory in the ITER vacuum vessel.”

The 26th IAEA Fusion Energy Conference held from 17-22 October provides a forum for the discussion of key physics and technology issues as well as innovative concepts of direct relevance to the use of nuclear fusion as a source of energy.