Russia, the United States, the European Union, China, India, Japan and South Korea are taking part in the $12.1 billion project, known by the acronym ITER, to demonstrate the scientific and technological potential of nuclear fusion amid concerns over growing energy consumption and the impact of conventional fossil fuels on the environment.
Yevgeny Velikhov, president of the Kurchatov Institute of Nuclear Physics, said an agreement on the project will be signed in Paris November 21.
"We expect substantive work to begin next January," he said, adding that the first plasma operation is expected in 2016.
The reactor will be built in France's Cadarache, with the European Union covering 40% of the costs and the other participants contributing 10% each.
The first electricity-producing fusion power plant is to be built by 2030, most probably in Japan, Velikhov said.
"We believe that by the end of the century, nuclear fusion will account for a significant proportion of the energy humanity generates for itself," Velikhov said, praising it as an environmentally benign and essentially inexhaustible power source.