How the world’s largest fusion experiment became a geopolitical chess match — and why Cadarache won over Rokkasho after years of deadlock.
By the turn of the millennium, the International Thermonuclear Experimental Reactor — later rebranded simply as ITER, Latin for “the way” — had survived more than a decade of design work, a major cost-driven redesign in 2001, and the temporary withdrawal of the United States in 1998. The project aimed to build the first fusion device capable of producing net energy gain (Q ≥ 10), and the question of where to build it carried enormous significance: the host would receive billions in construction spending, thousands of high-technology jobs, and decades of scientific prestige.1
By 2003, the competition had narrowed to two sites. The European Union proposed Cadarache, a nuclear research campus in southern France operated by the CEA (Commissariat à l’énergie atomique). Japan offered Rokkasho, a village in Aomori Prefecture on the northern tip of Honshu, already home to a nuclear fuel reprocessing plant. Both sites met the technical requirements — seismic stability, electrical grid capacity, cooling water, and access for heavy components — but each had political champions with conflicting agendas.2
The six original ITER parties — the EU, Japan, Russia, the United States, China, and South Korea — were split. The EU, Russia, and China backed Cadarache; Japan, the U.S., and South Korea supported Rokkasho. The ITER Agreement required consensus, and neither bloc would yield. Ministerial meetings in 2003 and 2004 ended without resolution. Behind the scenes, the dispute reflected deeper tensions: Europe argued that hosting ITER was essential to maintaining its fusion leadership after the closure of JET, while Japan saw the project as a catalyst for its broader nuclear technology strategy.3
The breakthrough came in June 2005 at a ministerial meeting in Moscow. Japan agreed to support the Cadarache site in exchange for a package of concessions known as the Broader Approach. Japan would host supplementary fusion research facilities, including the International Fusion Materials Irradiation Facility (IFMIF) engineering validation activity and a satellite tokamak center. Japanese industry would receive a disproportionate share of ITER procurement contracts, and a Japanese national would serve as the first ITER Director-General — a role filled by Kaname Ikeda. The deal also reserved for Japan a privileged position in any future demonstration reactor (DEMO) discussions.4
On June 28, 2005, the ITER parties formally selected Cadarache. Construction began in 2010. The site selection saga — five years of negotiation for a question that might have been resolved by a technical panel in months — illustrated a truth about megascience: the physics is often simpler than the politics.5