Harnessing fusion power in terrestrial conditions would provide sufficient energy to satisfy mounting demand, and to do so in a sustainable manner that has a relatively small impact on the environment.

[39] The second isotope, tritium, only occurs in trace amounts in nature and the estimated world's supply (mainly produced by the heavy-water CANDU fission reactors) is just 20 kilograms per year, insufficient for power plants.

[7] Site preparation has begun near Cadarache center, France, and French President Emmanuel Macron launched the assembly phase of the project at a ceremony in 2020.

Gorbachev first revived interest in a collaborative fusion project in an October 1985 meeting with French President François Mitterrand, and then the idea was further developed in November 1985 at the Geneva Summit with Ronald Reagan.

[62] This push for cooperation on nuclear fusion is cited as a key moment of science diplomacy, but nonetheless a major bureaucratic fight erupted in the US government over the project.

[63] However, Sakharov also supported broader civil liberties in the Soviet Union, and his activism earned him both the 1975 Nobel peace prize and internal exile in Russia, which he opposed by going on multiple hunger strikes.

This led to nuclear fusion cooperation being discussed at the Geneva summit and release of a historic joint statement from Reagan and Gorbachev that emphasized, "the potential importance of the work aimed at utilizing controlled thermonuclear fusion for peaceful purposes and, in this connection, advocated the widest practicable development of international cooperation in obtaining this source of energy, which is essentially inexhaustible, for the benefit of all mankind.

This meeting marked the launch of the conceptual design studies for the experimental reactors as well as the start of negotiations for operational issues such as the legal foundations for the peaceful use of fusion technology, the organizational structure and staffing, and the eventual location for the project.

[75] On 21 November 2006, at a ceremony hosted by French President Jacques Chirac at the Élysée Palace in Paris, an international consortium signed a formal agreement to build the reactor.

[76] Initial work to clear the site for construction began in Cadarache in March 2007 and, once this agreement was ratified by all partners, the ITER Organization was officially established on 24 October 2007.

[7] The start of the project can be traced back to 1978 when the European Commission, Japan, United States, and USSR joined for the International Tokamak Reactor (INTOR) Workshop.

[94][95] In 1985, at the Geneva summit meeting in 1985, Mikhail Gorbachev suggested to Ronald Reagan that the two countries jointly undertake the construction of a tokamak EPR as proposed by the INTOR Workshop.

[128] A solid confinement vessel is also needed, both to shield the magnets and other equipment from high temperatures and energetic photons and particles, and to maintain a near-vacuum for the plasma to populate.

[132] The inner wall of the containment vessel will have 440 blanket modules that are designed to slow and absorb neutrons in a reliable and efficient manner and therefore protect the steel structure and the superconducting toroidal field magnets.

[166] When the ITER tokamak is in operation, the plasma-facing units endure heat spikes as high as 20 megawatts per square metre, which is more than four times higher than what is experienced by a spacecraft entering Earth's atmosphere.

This facility was created at the Efremov Institute in Saint Petersburg as part of the ITER Procurement Arrangement that spreads design and manufacturing across the project's member countries.

According to the agency's website: F4E is responsible for providing Europe's contribution to ITER, the world's largest scientific partnership that aims to demonstrate fusion as a viable and sustainable source of energy.

However, under the terms of the EU–UK Trade and Cooperation Agreement, the United Kingdom initially remained a member of ITER as a part of Fusion for Energy following the end of the transition period on 31 December 2020.

Each member of the ITER project – The European Union, China, India, Japan, Korea, Russia, and the United States – has created a domestic agency to meet its contributions and procurement responsibilities.

Fusion for Energy, often referred to as F4E, was created in 2007 as the EU's domestic agency, with headquarters in Barcelona, Spain, and further offices in Cadarache, France, Garching, Germany, and Rokkasho, Japan.

It was reported in December 2010 that the European Parliament had refused to approve a plan by member states to reallocate €1.4 billion from the budget to cover a shortfall in ITER building costs in 2012–13.

The closure of the 2010 budget required this financing plan to be revised, and the European Commission (EC) was forced to put forward an ITER budgetary resolution proposal in 2011.

This system was devised to provide economic stimulus and fusion expertise in the countries funding the project and the general framework called for 90% of member contributions to be in material or components and 10% to be in money.

[227] According to a 2017 estimate from French Minister for Research, Education and Innovation, Frédérique Vidal, there were 500 companies involved in the construction of ITER and Bernard Bigot stated that €7 billion in contracts had been awarded to prime contractors in Europe alone since 2007.

[228][229] The overall assembly of the tokamak facility is being overseen through a €174-million contract awarded to Momentum, a joint venture between Amec Foster Wheeler (Britain), Assystem (France), and Kepco (South Korea).

[230] One of the largest tenders was a €530-million contract for HVAC systems and mechanical and electrical equipment that was awarded to a European consortium involving ENGIE (France) and Exyte (Germany).

[232] The French industrial conglomerate Daher was awarded more than €100 million in logistics contracts for ITER, which includes the shipment of the heavy components from the different manufacturers around the world.

[7] The ITER project has been criticized for issues such as its possible environmental impacts, its usefulness as a response to climate change, the design of its tokamak, and how the experiment's objectives have been expressed.

[245] Other critics, such as Daniel Jassby, accuse ITER researchers of being unwilling to face up to the technical and economic potential problems posed by tokamak fusion schemes.

According to published safety assessments (approved by the ASN), in the worst case of reactor leak, released radioactivity will not exceed 1/1000 of natural background radiation and no evacuation of local residents will be required.