A first examination in 2002
In June 2005, the seven partners involved in the project, namely Russia, United States, Europe, Japan, China, South Korea and India, signed an agreement selecting the Cadarache site, near to Aix-en-Provence, for the installation of the ITER international project. Consequently, in 2002, IRSN was first mandated to examine the safety options of the experimental facility.
“We concluded, from this first examination, that the general principles retained were suitable but that, if the project were to continue, certain additional points needed to be reconsidered, such as the risk of explosion in the vacuum chamber”, recalls Didier Perrault.
Key ITER dates from its conception to its operational commissioning
1985 – Launch of the ITER programme by Russia, United States, the European Union (via EURATOM) and Japan.
1988 – Design studies.
2002 – Examination of the ITER safety options file by IRSN.
2003 – China and South Korea join ITER.
2005 – India joins ITER.
2005 - The Cadarache site (Bouches-du-Rhône) is selected.
2005 – IRSN begins specific ITER research work.
2006 – 21 November, official signature for the creation of the international legal entity ITER Organization, charged with the construction and operation of ITER.
2008 – Start of the examination by IRSN of the application for authorization to build ITER.
2010 – Start of excavation works on the site (excavation).
2011 – Start of construction of the tokamak complex.
2011 - IRSN presents its ITER safety expert appraisal to the permanent expert groups of ASN.
2012 to 2014 – ITER responses to the questions of ASN.
2015 – Start-up of the assembly of the tokamak.
2020 – Tokamak completed. First hydrogen plasma (without radioactive material).
2027 – Installation operational. Start of nuclear fusion reactions.
In 2006, when the decision to install ITER in France was confirmed, IRSN identified research actions that needed to be carried out within the Institute. The results of theses researches could be useful with a view to future expert appraisals of the safety of the ITER facility, particularly with regard to the sensitive subject, already broached, of an explosion in the event of air entering via a vacuum chamber crossing.
“We already have expertise in the explosion of hydrogen in the containment vessels of pressurized water reactors, even if it involves fission and not fusion”, continues Ahmed Bentaib, explosion specialist at IRSN. “We have adapted our modeling tool to ITER conditions: the areas of application of the Astec and Tonus calculation codes have been extended to low pressures in order to simulate the accidents that could occur in the vacuum chamber. We have also developed new tools, such as the Dust code, to predict the mobilization, the transport and the explosion of dusts from the erosion of the internal walls of the vacuum chamber.”
In parallel, a PhD thesis was devoted to studying the question of the combustion of hydrogen in the presence of dust. Finally, external expertise has been sought, such as that of Benjamin Carreras, an American plasma specialist: “Disruptions can occur in this type of apparatus, leading to a sudden drop in the plasma current, which creates very high voltages in the chamber and causes the acceleration of electrons, which can damage the structure”, explains the consultant.
An examination for the creation of the facility handed over in 2011
This expertise enabled IRSN to conduct an examination of the safety of the ITER facility with a view to its creation. This examination, which began in 2008, was carried out based on the application for authorization to develop the facility handed over by the operator, comprising more than 4 000 pages, along with some 700 responses and 100 complementary documents.
The examination was concluded in 2011 with the publication of a 400-page report, containing 200 recommendations, which were presented to the permanent working groups of ASN. “The research work that we have carried out since 2006 has allowed us to examine, among other things, the problem of an explosion in the vacuum chamber”, continues Ahmed Bentaib.
In practice, ASN will, on this basis, formulate to ITER the points for which the organization needs to provide an answer. “We have already proposed scheduling a new examination of the situation in three years” explains Didier Perrault. “In fact, this set of recommendations and the ensuing responses of ITER may lead to design modifications or complementary measures and it would not be reasonable to await the next meeting planned for 2021, the commissioning date, to conduct the examination. In practice, such an application is out of the ordinary. However ITER is a very particular system, of a unique design.”
Three years to prepare
Between now and this next milestone, IRSN experts have already programmed vital research to reinforce the expert appraisal of the ITER proposals.
“With regard to the question of an explosion, ITER is going to propose countermeasures such as hydrogen recombiners, which transform this gas into water, or ignitors, devices that burn the hydrogen as it is produced. These two countermeasures have a single and same purpose: to avoid a dangerous build-up of hydrogen”, summarizes Ahmed Bentaib. “We are now going to develop simulations in order to evaluate the relevance of these devices in the case of ITER.”
The analysis of accidental scenarios is also planned. “We are going to continue the evaluation of the scenarios studied by the ITER teams to ensure that we arrive at the same results, but also to explore hypotheses that have not been studied and which, in our opinion, are worth investigating.” Objective: to be ready when ITER provides responses to the points raised by ASN.