[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. Launched in 2006, the colossal ITER scientific program, aimed at proving that fusion (power from the Sun and stars) could one day generate immense amounts of carbon-free electricity, is facing problems of ” big size according to a statement released last night by the ITER Organization. Which takes away the hope of a first full-power nuclear fusion from 2035 in this gigantic experimental machine, located in Cadarache (Bouches-du-Rhône) and the result of the cooperation of 35 countries.
In fact, cracks up to 2.2 millimeters deep have been identified in several key components of the tokamak, the famous donut-shaped structure within which the melting will take place. The latter consists of heating isotopes of hydrogen, deuterium and tritium, to 150 million degrees, then in the form of plasma, to release enormous amounts 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 currently operating nuclear power plants.
Affected heat shields
Only here: Corrosion defects affect “ heat shields and vacuum vessel sectors “, specifies ITER in its press release. However, these fulfill an important function, since they are supposed to limit the heat transfer between the areas of very high temperature and those that need to be kept at a very low temperature. And for good reason, the vacuum chamber where the 150 million degree fusion will take place will be just a meter away from magnetic coils, cooled in liquid helium to -269°C to be superconducting (c meaning perfectly conducting a current, no resistance, and therefore no loss of energy). ” The thermal shields are silver-coated pieces located between these two sectors, whose objective is to minimize the heat flow between them. “, specifies to The galery Greg de Temmerman, scientific coordinator of the ITER project between 2014 and 2020. And thus protect the superconducting magnetic system that will create the plasma.
In detail, these leaks had already been detected in November 2021 during helium tests ” on a heat shield element of the vacuum vessel » delivered a year and a half earlier by Korea, without ITER communicating about it. Working groups were then created to investigate, with experts from different partners of the organization. so they were able to identify the root cause ” of the problem, underlines the press release: a ” stress caused by bending and welding of refrigerant pipes […] aggravated by a slow chemical reaction due to the presence of residual chlorine. In other words, a weakness in the design of the cooling hose fitting made it impossible to remove residual chlorine, resulting in ” stress corrosion in the lines
“A Crucial Question [s’est alors posée] : Was the problem specific, limited to the items examined, or was it systemic, affecting all components of the heat shield? asks ITER, in an exercise of transparency.
” We must assume that the problem extends “, answers 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 severe not to check it. And for good reason, during the famous nuclear meltdown, the vacuum chamber must contain tritium, a radioactive element. ” The calculations have been done so the structure never has to break. […] The magnetic geometry must be as perfect as possible to confine the plasma, because each misalignment can be very expensive. says Greg of Temmerman.
Shown 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 Reynal
several more years late
Therefore, the problem will require a ” thorough examination “, of the ” creativity in the design of corrective actions ” as much as ” time and budget to remedy it, recognize. And for cause, ” process it in the hole [du tokamak] in the already assembled module it would be extremely difficult “says the press release. This means that said module will have to be lifted, to be able to disassemble it and then carry out the repairs.
“We are exploring different possibilities, from on-site repair to remanufacturing in an outdoor facility, possibly with different pipe fixing options. But there is no doubt about the need to replace the refrigeration pipes”, explains the organization.
The additional cost of this unforeseen event remains to be known, although the bill has increased since the start of the project, going from 5,000 million euros at the start to more than 20,000 million today. Nevertheless, “ almost 90% of the budget is made without direct money, since it comes from contributions in kind from the different countries, through the supply of the buildings, parts and systems of the installation remembers Greg of Temmerman.
Therefore, the main question will be related to the expected delay. Prior to the incident, the first non-fusion test operations, hitherto scheduled for 2025 (versus 2016 initially), were already headed for a further delay of at least two years. With this new event, it is clear that the delay will be counted again in years says Greg of Temmerman. However, the official estimates should not arrive until next May, when the high-level representatives of each of the member countries involved in the project meet in Council.
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