Posted on: 25th March 2013

The Japanese people have a long history of creating ceramics of great beauty and elegance. Now they are putting their skills towards the search for materials for future fusion plants – in this case not crafting elegant forms, but elegant solutions: ceramics are nearly impervious to tritium.

In a colloquium delivered at JET last week, Assistant Professor Takumi Chikada from the University of Tokyo outlined promising progress in research into the ceramic coating, erbium oxide, which may prove to be a vital coating for use in tritium-carrying pipework. “Without solving this problem it will be impossible to operate a fusion reactor,” he stated.

Because of its very small size, tritium tends to permeate through materials readily – an undesirable characteristic in a tritium processing plant, where tritium would be exposed to a large surface area as it passes through cooling, ducting and processing pipework.

Assistant Professor Chikada’s results showed that a layer of erbium oxide only tens of microns thick on a steel surface could reduce permeation of tritium by 100 000 times. Erbium oxide was originally chosen as an insulation coating because it has a high thermodynamic stability and is resistant to liquid lithium-lead – a proposed blanket material for fusion plants, which is corrosive to many materials.

Other materials are also being studied as tritium barriers, for example in the Karlsruhe Institute of Technology (KIT) which investigates aluminium oxide. It is unclear which coating will turn out to be the most suitable – erbium oxide and aluminium oxide each have advantages, but experiments to date have been with small samples, which can suffer from flaking if the wrong manufacturing process is used. Also irregularities in the crystal structure of the oxide can provide paths for tritium to permeate through.

“The development path is stony for barriers in the lab,” says Dr Wolfgang Krauss from KIT. “We must guarantee the quality (no defects, smooth surface etc) and qualify the barriers under irradiation. Also industrial relevance must always be considered.”

However as manufacturing techniques improve and explore multiple coatings of varied materials, it is likely that a good solution will be discovered, so we can be confident that the tritium will go where we want it to go – back into the tokamak!

Karlsruhe Institute of Technology is one of three German signatories to EFDA