[Article mis à jour le 22/11/2022 à 17:36 avec les explications de Greg de Temmerman, coordinateur scientifique du projet ITER entre 2014 et 2020]
It’s a blow to one of the world’s most ambitious energy projects, with likely far-reaching consequences in terms of schedule and cost. Initiated in 2006, the colossal scientific program ITER, supposed to demonstrate that fusion (the energy of the Sun and the stars) could one day generate immense quantities of carbon-free electricity, is indeed confronted with problems of ” grande dimension », according to a statement released by the ITER organization last night. What remove the hope of a first nuclear fusion at full power from 2035 in this gigantic experimental machine, located in Cadarache (Bouches-du-Rhône) and resulting from the cooperation of 35 countries.
Indeed, cracks reaching up to 2.2 millimeters deep have been identified in several key components of the tokamak, the famous donut-shaped structure inside which the fusion will take place. The latter consists of heating isotopes of hydrogen, deuterium and tritium, to 150 million degrees, then in the form of plasma, in order to release huge quantities of energy absorbed by the walls of a vacuum chamber located in this tokamak. A chain reaction that generates almost no waste, unlike the fission of heavy uranium nuclei, used by all nuclear power plants in operation today.
Heat shields affected
Only here: the corrosion defects affect “ heat shields and vacuum vessel sectors “, specifies ITER in its press release. However, these perform a major function, since they are supposed to limit the heat transfer between the very high temperature zones and those requiring to be maintained at very low temperature. And for good reason, the vacuum chamber where the fusion will take place at 150 million degrees will only be about one meter away from magnetic coils, cooled in liquid helium at -269°C in order to be superconducting (c that is to say perfectly conducting a current, without resistance, and therefore without loss of energy). ” Heat shields are silver-coated parts located between these two sectors, which aim to minimize heat flow between them “, specifies to the Tribune Greg de Temmerman, scientific coordinator on the ITER project between 2014 and 2020. And thus protect the superconducting magnetic system that will create the plasma.
In detail, these leaks had been detected as early as November 2021 during helium tests ” on an element of the heat shield of the vacuum vessel » delivered a year and a half earlier by Korea, without ITER communicating on this subject. Working groups were then created to investigate, with experts from different partners of the organization. which were able to identify the root cause ” of the problem, underlines the press release: a ” stress caused by bending and welding of coolant pipes […] aggravated by a slow chemical reaction due to the presence of chlorine residues. In other words, a weakness in the design of the cooling hose attachment made it impossible to remove residual chlorine, resulting in ” stress corrosion cracking in the pipes.
“A crucial question [s’est alors posée] : was the problem punctual, limited to the examined elements, or was it systemic, affecting all the components of the heat shield? asks ITER, in an exercise in transparency.
« We have to assume that the problem is extended “, replies its general manager, Pietro Barabaschi, through the press release. And to add that ” the risk is too high and the consequences of a thermal protection panel leaking during operation are too serious so as not to verify it. And for good reason, during the famous nuclear fusion, the vacuum chamber must therefore contain tritium, a radioactive element. ” The calculations have been made so that the structure never has to break. […] The magnetic geometry must be as perfect as possible to confine the plasma, because each misalignment can be expensively paid », explains Greg de Temmerman.
Above is one of the modules of the vacuum vessel, supplied by Korea, which will constitute the stainless steel vacuum chamber in which the fusion reactions will take place, and which must be perfectly hermetic. ©Juliette Raynal
Several more years of delay
Therefore, the problem will require a ” thorough examination “, from ” creativity in the design of corrective actions ” as well as ” time and budget in order to remedy this, he acknowledges. And for good reason, ” process it in the pit [du tokamak] on the already assembled module would be extremely difficult “says the press release. This means that said module will have to be lifted, in order to dismantle it and then carry out repairs.
“We are exploring different possibilities, from on-site repair to re-fabrication in an outdoor facility, possibly with different pipe attachment options. But there is no doubt about the need to replace the cooling pipes,” explains the organization.
It remains to know the additional cost incurred by this unforeseen, while the bill has increased since the beginning of the project, from 5 billion euros at the start to more than 20 billion currently. However, “ almost 90% of the budget is done without direct money, since it comes from in-kind contributions from the different countries, through the supply of the buildings, parts and systems of the installation recalls Greg of Temmerman.
The main question will therefore relate to the delay to be expected. Before the incident, the first test operations without fusion, so far planned for 2025 (against 2016 initially), were already heading for an additional delay of at least two years. With this new event, it is clear that the delay will again be counted in years says Greg de Temmerman. However, the official estimates should not arrive before next May, when the high-level representatives of each of the member countries involved in the project will have to meet in Council.