The seven partners in the International Thermonuclear Experimental Reactor (ITER) - Europe, United States, China, India, Japan, Russia and South Korea - launched the project 10 years ago with a 5 billion euro ($5.6 billion) cost estimate and plans to heat the first plasma by 2020 and achieve full fusion by 2023
In May, new ITER chief Bernard Bigot - former head of French nuclear state agency CEA - told a French newspaper ITER would be delayed by more than a decade and incur another 4 billion euros of cost overruns, with the first test of its super-heated plasma not before 2025 and its first full-power fusion not before 2035.
"For the first time, we have a reliable estimate ... In the past there was no realistic schedule, no detailed appreciation of the cost ... It was much underestimated," said Bigot, who succeeded Japan's Osamu Motojima as ITER head early last year.
The running cost of the ITER organisation plus the domestic agencies in the partner countries is about 200 million euros per year. Any delay to the project automatically increases the cost by that much.
Partner countries contribute about 80 percent of the value of the project in kind, it is difficult to give precise cost estimates. "This is the source of the inaccuracy when we try to compile the total number," he said.
"If all partner countries had European levels of cost and bureaucracy and you extrapolate based on European costs, it would be at the higher end of the range ... Cost could be up to 22 billion euros at the maximum," he said.
Construction at the ITER site in rural Cadarache got under way in 2013-14, but has accelerated from April-May 2015 onwards.
"We have seen more progress in the last six months than in the last three years," Coblentz said.
Laurent Schmieder, head of construction at ITER, said by 2019 the building that will house the so-called tokamak fusion reactor will be complete. The cost of the buildings alone at the complex will be about 2 billion euros, he said.
ITER is designed to produce approximately 500 MW of fusion power sustained for up to 1,000 seconds (compared to JET's peak of 16 MW for less than a second) by the fusion of about 0.5 g of deuterium/tritium mixture in its approximately 840 m3 reactor chamber. Although ITER is expected to produce (in the form of heat) 10 times more energy than the amount consumed to heat up the plasma to fusion temperatures, the generated heat will not be used to generate any electricity
So the goal is to demonstrate significant net power gain but only the follow on projects would be a prototype of a commercial reactor.