News & Analysis Physics World  August 2017

Europe puts key project on hold over exhaust issue

Hot topic The Divertor Tokamak Test facility will test different shapes of divertor to see what might work best in a demonstration fusion reactor. (Elsevier / Nuclear Mat. & Energy 10.1016 / j.nme.2017.05.008)

A split has emerged between Italy and other European nations over how to tackle one of fusion energy’s biggest problems – getting rid of reactors’ extremely hot exhaust. The 20bn ITER reactor currently being built in the south of France will use a conventional tungsten-based “divertor” to remove the enormous amounts of energy dumped on the reactor’s wall by stray plasma particles. But this device is likely to be inadequate for ITER’s planned successor – a demonstration power plant that would feed electricity to the grid continuously.

Scientists and engineers at ENEA, Italy’s energy and technology agency, have drawn up plans for a 500m reactor known as the Divertor Tokamak Test facility (DTT) to investigate alternative types of divertor. The superconducting machine, which is intended to be up and running by 2025, would have space around the edges of its plasma chamber to incorporate divertors of various shapes to spread the heat load over a larger area. It could also test divertors made of more resistant materials, such as liquid lithium.

The DTT design was submitted to EUROfusion, a consortium of European research organizations, following a call in 2015 for proposed heat-exhaust projects. But an expert panel reviewing the proposals recommended last year that a decision on whether to fund the DTT be delayed pending results from smaller projects that involve upgrading existing facilities to carry out proof-of-principle studies of specific divertors. Waiting, argued the panel, would yield a more focused, and therefore cheaper, design, and would also allow the project to be scrapped in the unlikely event that ITER shows a conventional divertor could be adapted to withstand harsher conditions.

Undeterred, the Italian researchers made their case for an immediate decision at a workshop held in Frascati, south of Rome, in June. At the meeting, representatives of EUROfusion insisted that a formal decision be put on ice. However, the two sides did eventually reach a compromise. EUROfusion agreed “in principle” to commit 60m in around 2022/3, regardless of results from the smaller projects, so long as ENEA makes good progress on construction in the meantime. The Italians must also show by the end of this year that their design will be flexible enough to incorporate the full range of possible divertors.

That agreement still needs formal approval by EUROfusion’s member organizations when they meet in a general assembly later this year. The consortium’s programme manager Tony Donné says a subset of members charged with organizing the assembly did not suggest any changes to the deal reached in Frascati. But he stresses that until EUROfusion makes a formal decision in a few years’ time it bears no risk for any problems that may occur. “For the moment the project is purely Italian,” he says.

Flavio Crisanti of ENEA is nevertheless hopeful that the agreement will persuade the Italian government to approve its proposed share of the funds – about €120m – by the turn of the year. The idea then, he says, is that 250m would be provided by a loan, possibly from the European Investment Bank, while the balance would be paid for by ENEA, the regional government and China.

Edwin Cartlidge

Rome