Opened helium cold box. Image: Air Liquide
“For ITER, Air Liquide is an industrial partner and not just a supplier,” says Sergio Orlandi, head of department plant engineering for ITER. “We have succeeded in creating a very fruitful cooperation, which at the end we believe will bring solutions and positive results.”
ITER will feature the world’s largest Tokamak, a Russian-origin technology that uses magnetic fields to confine fusion. The ITER Tokamak will have a plasma volume of 840 m3—the world’s largest—and is expected to demonstrate the scientific and technological feasibility of fusion as a source for producing electricity that does not release CO2 and that can be used on a large scale.
In nature, fusion results from collisions of hydrogen nuclei, but under experimental conditions it is carried out with hydrogen’s cousins, deuterium and tritium. The goal of ITER is to recover at least 10 times the energy consumed (Q 10). To do so, three conditions must be met: a temperature of around 150 Millions°C, great particle density and long confinement of the energy. Fusion thus requires that gas be transformed into plasma. This is done inside a Tokamak, where hot plasma is confined and controlled by strong magnetic fields created by superconducting magnets. About 80 percent of the energy released, carried by the neutron, is absorbed by the walls of the Tokamak. This creates heat, which in turn produces steam that is converted into electricity using turbines and alternators.
Some 10,000 tons of superconducting magnets will be used to confine this energy-generating plasma, requiring a robust cryogenic system to keep the magnets cold. A large cryostat and a thermal shield with a forced flow of helium at 80 K (-193 °C) will surround the magnets. A cryoplant on the ITER platform will produce the required cooling power and distribute it through a complex system of cryolines and cold boxes. Air Liquide began designing the cryogenic factory dedicated to this end in 2013 and is now in the fabrication phase. Installation at the ITER facility in Cadarache, France, is scheduled for 2017.
The Air Liquide factory will feature a centralized cryogenic refrigeration system composed of helium and nitrogen refrigeration units and dedicated storage, functioning in a closed loop. Helium, which is capable of reaching temperatures near absolute zero (-269 °C, or 4.5 K), will be used to cool the magnets, vacuum pumps and certain diagnostic systems. Engineers will use nitrogen (-196 °C, or 77 K) to cool the heat shield and to provide pre-cooling to the helium refrigeration unit and helium loops.
The site’s three helium units (LHe) will occupy 3,000 m2 of the 5,400 m2 set aside for the ITER cryogenic unit. LHe is composed of several compression stations and three large cold boxes that weigh 135 tons each, measure 21 meters in length and have a diameter of 4.2 meters. On average, the helium refrigeration units will provide a global cooling capacity of 75 kW at 4.5 K or a maximum liquefaction rate of 12,300 liters/hour. In total, 11 helium and nitrogen gas storage units—with a total capacity of 3,700 m3 (of which 3,300 m3 is for the helium)—will help optimize the recovery of fluids in the various operational phases of the Tokamak.
Air Liquide is also working on a project for ITER India to design and fabricate 19 cryogenic lines that will complete the Cadarache cryogenic plant by distributing the cooling power needed for the ITER equipment to run. Dedicated to helium, this 1.6 km long network will link the cryogenic plant to the Tokamak between 2017 and 2019.
“The cryogenic system of ITER is, after CERN, one of the most complex systems known to date,” says Dr. Biswanath Sarkar, ITER India’s project manager. “ITER India teams are happy to be associated with Air Liquide teams in this technological and scientific adventure.”
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