On the pharaonic construction site of the prototype of the ITER nuclear fusion reactor at the Cadarache site (Bouches-du-Rhône), it is not just the workers who are busy. The engineers had to change their priorities to respond quickly to the long list of requests from the Nuclear Safety Authority (ASN), so that the assembly of this unique machine in the world continues on schedule.
ASN's requests, in the form of a letter addressed by its chairman to the director general of the international organization ITER, were revealed on 21 February by the news site New Energy Times, which is highly critical of the energy of merger. The missive is not good news. It indicates that, as it stands, the assembly of the reactor cannot begin, in particular the key and irreversible stage of welding the first two elements together, out of nine, constituting the vacuum chamber 19.4 meters in diameter and 11.4 meters high, in which the fusion reactions must take place.
Unlike nuclear fission, which breaks uranium nuclei to release energy, here, as in stars, light hydrogen nuclei are forced together. For this fusion to take place, it is necessary to bring the nuclei together and heat them to 150 million degrees long enough to produce more energy than that needed to initiate the reaction. This technique, called "tokamak", uses intense magnetic fields to confine matter.
The ITER project, decided in 2006 and bringing together six countries and the European Union, must demonstrate the viability of this large-scale solution from 2025, at a construction cost of around 20 billion euros. In 2012, when the ASN agreed to start the work, three so-called “stopping points” were planned as so many appointments to be honored for the continuation of operations. In 2014, for the pouring of the concrete screed (the slab), and in 2016, for the external heating devices, these steps had been completed.
But, on January 25, one year after its request for "lifting of the third stop point", ITER received the negative response from the ASN: "The stop point linked to the tokamak assembly cannot be lifted (…). As a result, the tokamak assembly cannot be engaged. “The latter was to take place” towards the end of 2022 “, explains Laban Coblentz, director of communication for ITER. He adds: “The construction site is not stopped. This letter does not interrupt work. This is a usual phase of dialogue with the regulator. It must also be said that we are dealing with a machine which is the first of its kind and which is very complex. »
On the first two elements of the vacuum chamber, work continues, in fact, to weld reinforcement parts and electric coils. They are still in the assembly hall and the first could be lowered into the main shaft in "a few weeks", estimates Laban Coblentz.
ASN is in fact asking for additional information to guarantee safety and control of radiation protection within the installation on seven points. First, on the resistance of the materials to the flux of neutrons emitted during the reactions. “ITER did not provide all the elements for us to position ourselves,” recalls Bastien Lauras, head of the Marseille division of ASN.
Then, during collisions with the surfaces of the vacuum chamber, these neutrons make radioactive nuclei in the enclosure. ASN therefore also requests "radiological maps" to estimate the radiation on the installation and to confirm that the safety of the workers will be ensured. It also indicates that it is necessary for ITER to demonstrate that the concrete slab will indeed support any excess weight linked to the addition of possible additional protections. Similarly, it requires a more complete assessment of the various radioactive sources present during operation or in the event of an accident of the machine. Just as it requires new demonstrations of the facility's resistance to the effects of an earthquake, to take account of experience feedback from the Fukushima accident, like what was requested for nuclear facilities classics.
Finally, two other requests relate to defects observed during manufacture. The slab, capable of supporting the 400,000 tons of the complete machine, rests on 493 anti-seismic pillars, but it has risen a little at the edges. ASN asks that this be taken into account in the final safety demonstration.
In a letter made public by New Energy Times, Bernard Bigot, the director general of ITER, assures that the Spaniards have found a solution. Laban Coblentz believes that all the answers can be provided "in April or May". "ITER must submit a new file so that we can investigate it", specifies Bastien Lauras. For the first stopping point, ITER had planned to pour the concrete in 2013 but had not been authorized to do so until more than a year later by the ASN.
The next few months will therefore be decisive, as several other events are pending. The European part of ITER, the agency Fusion For Energy (F4E), is also awaiting the results of an investigation, but this time on the working conditions within it. In May 2021, an engineer indeed committed suicide. Then, in November, a staff strike prompted management to request an additional investigation into the circumstances of this death. Before parliamentarians from the budget control committee on February 28, Johannes Schwemmer, the director of F4E, acknowledged that psychological support had been put in place and that the workload, with "98 projects to be carried out by 440 people was very important. Union representatives spoke of “lack of social dialogue” and “toxic management”.
Next June, the ITER council will meet and “study proposals for schedule and cost revisions,” according to Laban Coblentz. In September 2021, Bernard Bigot also considered it “untenable” to start test operations without a merger, in 2025, as planned. From now on, the ITER communication prefers to mention not this stage, but the later stage of the first fusion reactions, announced for 2035.
The European Court of Auditors warned, in its 2021 report, that “any change in the main assumptions underlying the estimation and the risk exposure could lead to significant cost increases and/or further delays”. Premonitory, perhaps, it stipulated that “the French nuclear safety authority has the last word, and [that] any future modification of the requirements in this area could have a significant financial impact”.
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