Deuterium

Pellet injection advances to next stage in the US

Researchers at the Oak Ridge National Laboratory (ORNL) have developed a continuous extruder for fusion fuel and are advancing state-of-the-art fuelling and plasma control for ITER. Reliable, high-speed continuous fuelling is essential for ITER to meet its goal of operating at 500 MW for several minutes at a time. The latest pellet injection experiments using US ITER prototype designs were performed during the week of 22 July at the DIII-D Tokamak operated by General Atomics in San Diego, California. The conceptual design review for the ITER pellet injection system was completed earlier this year, and preparations are now underway for full-scale prototype testing. The task of the pellet injection system is to provide plasma fuelling, while also lessening the impact of plasma instabilities due to large transient heat loads. The ITER pellet injectors must operate continuously, which is very different from most existing tokamak pellet injectors. The ITER machine also requires a higher rate of pellet fuelling throughput. According to Dave Rasmussen, team leader for the US ITER pellet injection and disruption mitigation systems, „The ITER pellet injectors will require an increase in the deuterium-tritium mass flow and duration by a factor of 1,000 compared to present systems.” To produce the pellets, researchers developed a twin-screw extruder which shapes a continuous ice stream of deuterium-tritium fuel into specific diameters and lengths. „There are existing extruders used on tokamaks today, but they cannot meet the requirements of ITER. On most current installations, extruders have only needed to supply a few seconds of fuel pellets at a time, but the ITER Tokamak will require almost an hour of a continuous ice stream for pellet injection. The ORNL twin-screw extruder is designed to meet t Czytaj dalej...

Melting tungsten for a good cause

Over the past two years ITER physicists and engineers, along with many scientific colleagues within the fusion research community, have been working to establish the design and physics basis for a modified divertor—the component located at the bottom of the huge ITER vacuum vessel responsible for exhausting most of the heat and all of the particles which will continuously flow out of ITER’s fusion plasmas.  Our current Baseline begins plasma operations with divertor targets armoured with carbon fibre composite (CFC) material in the regions that will be subject to the highest heat flux densities. After the initial years of ITER exploitation, in which only hydrogen or helium will be used as plasma fuel producing no nuclear activation, this divertor is to be replaced. The replacement—a variant of the first component but fully armoured with tungsten—would be the heat and particle flux exhaust workhorse once the nuclear phase, using deuterium and then deuterium/tritium fuel, begins. In 2011 the ITER Organization proposed to eliminate the first divertor and instead go for the full-tungsten („full-W”) version right from the start. This makes more operational sense and has the potential for substantial cost savings. By June 2013, the design was at a sufficiently advanced stage and we were confident that the necessary tungsten high heat flux handling technology was mature enough to invite external experts to examine our progress during the full-W divertor Final Design Review.  But making a choice to begin operations with tungsten in the most severely loaded regions of the divertor is not just a question of having a design ready to build.  Tungsten, a refractory metal with high melting temperature (3400 Celsius), is a much more difficult material than carbon when it comes Czytaj dalej...

Green light for ITER’s blanket design

After three days and 29 presentations, a comprehensive design review with probably the largest participation in the history of the ITER project was completed last week. More than 80 experts from the ITER Organization, Domestic Agencies and industry attended the Final Design Review of the ITER blanket system. „The development and validation of the final design of the blanket system is a major achievement on our way to deuterium-tritium operation—the main goal of the ITER project,” Blanket Integrated Product Team Leader (BIPT) and Section Leader Rene Raffray concluded at the end of the meeting, obviously relieved at the success of this tremendous endeavour. „We are looking at a first-of-a-kind fusion blanket which will operate in a first-of-a-kind fusion experimental reactor.” The ITER blanket system provides the physical boundary for the plasma and contributes to the thermal and nuclear shielding of the vacuum vessel and the external machine components such as the superconducting magnets operating in the range of 4 Kelvin (-269°C). Directly facing the ultra-hot plasma and having to cope with large electromagnetic forces, while interacting with major systems and other components, the blanket is arguably the most critical and technically challenging component in ITER. The blanket consists of 440 individual modules covering a surface of 600 m2, with more than 180 design variants depending on the segments’ position inside the vacuum vessel and their functionality. Each module consists of a shield block and first wall, together measuring 1 x 1.5 metres and weighing up to 4.5 tons—dimensions  that not only demand sophisticated remote handling in view of maintenance requirements during deuterium-tritium operation, but also an approach to attaching the modules which is far from trivi Czytaj dalej...

EUR 83 million contract signed for Liquid Helium Plant

The ITER Tokamak will rely on the largest cryogenic plant (cryoplant) infrastructure ever built. Three liquid helium plants, working in parallel, will provide a total average cooling capacity of 75 kW at 4.5 K and a maximum cumulated liquefaction rate of 12,300 litres/hour. On Tuesday, 11 December, ITER Director-General Osamu Motojima and the Managing Director of Air Liquide Advanced Technologies, Xavier Vigor, signed the contract for ITER’s three identical liquid helium (LHe) plants. The contract comprises the design, manufacturing, installation and commissioning of the LHe plants, which are adapted to the long-term, uninterrupted operation of the ITER Tokamak. The contract is worth EUR 83 million. The cryoplant and cryo-distribution system will supply cooling for the ITER superconducting magnets to confine and stabilize the plasma. They will also provide the refrigeration for the cryosorption panels that are necessary to evacuate the helium ashes stemming from the fusion reaction and to assure the required vacuum for the cryostat and the vacuum vessel. All these users require helium cryogen at different temperature levels ranging from 4.5 K, to 50 K and up to 80 K. The key design requirement is to cope with ITER’s large dynamic heat loads ranging from 40 to 110 kW at 4.5 K mainly deposited in the magnets due to magnetic field variation and neutron production from deuterium-tritium fusion reactions. At the same time, the system must be able to cope with the regular regeneration of the cryopumps. Manufacturing of the LHe plant main components will start after design finalization in 2014. The first compressor station will be delivered at the end of 2015 and the LHe plants will be ready for the cool-down of sub-systems in 2018. „This is a major milestone not only for the cryogenic syste Czytaj dalej...

Deuterium from a quantum sieve

A metal-organic framework separates hydrogen isotopes more efficiently than previous methods Deuterium is the heavy twin brother of hydrogen; however, it is more than 20 times rarer than identical twins. It accounts for only 0.015 percent of natural hydrogen and is twice as heavy as the light isotope. There is no chemical difference between the two isotopes: both deuterium and ordinary hydrogen react with oxygen to form water. Its double mass allows researchers to lay a trail to elucidate chemical reactions or metabolic processes, however. They dispatch a compound containing deuterium into the processes and analyze in which conversion product it turns up. And this is only one of the tasks that deuterium fulfils in research. It may even become an inexhaustible and climate-neutral fuel in future. This would be the case if nuclear fusion becomes so technically mature that energy is generated on Earth using the same process that also occurs in the Sun. This produces much less radioactive waste than nuclear fission. In a cooperation established within the DFG German Research Foundation’s priority program „Porous Metal-Organic Frameworks” (SPP 1362), a team of scientists from the Max Planck Institute for Intelligent Systems in Stuttgart, Jacobs University Bremen and the University of Augsburg have now been able to enrich deuterium contained in hydrogen more efficiently than with conventional methods. The findings are reported in the journal Advanced Materials. The researchers discovered that a certain metal-organic framework, abbreviated MOF, absorbs deuterium more easily than common hydrogen at temperatures below minus 200 degrees Celsius. Read more here.  Czytaj dalej...

Tore Supra ready to go WEST

On the other side of the CEA fence, in Cadarache, sits a large tokamak which played an important role in the definition of ITER. Tore Supra, a CEA-Euratom device which began operating in 1988, was the first tokamak to successfully implement superconducting magnets and actively-cooled plasma-facing components. Over the past twenty-four years, Tore Supra has explored the physics of long-duration plasma pulses, reaching a record of 6.5 minutes in December 2003. In 2000-2002, Tore Supra was equipped with a new carbon-carbon fibre (CFC) „limiter” — the equivalent of the divertor in ITER — capable of withstanding an ITER-relevant heat load of 10 MW per square metre. This project, named CIEL for Composants Internes Et Limiteurs, demonstrated that, while CFC performs very well in terms of power handling and compatibility with the plasma, its use results in substantial erosion caused by the physico-chemical reactions between the carbon of the limiter and the hydrogen (deuterium) in the plasma. Further experiments in JET have confirmed these observations. Now, there are not many options when it comes to choosing the material of a divertor. Fifty years of experience in tokamak technology have narrowed them to two: it’s either CFC or tungsten, their respective advantages or disadvantages depending on the plasma regimes they are exposed to. (More here). In ITER, it was originally planned to begin operations with a CFC divertor and replace it with a tungsten one before the start of nuclear operation (deuterium + tritium) in 2026. After years of discussions, panels and reviews, a new plan was established and ITER is now considering doing without the first-phase CFC divertor. Indeed, substantial cost reductions would be achieved by installing a tungsten divertor right from the start and o Czytaj dalej...

One more step towards the final green light

On 29 July, a new milestone was reached in the licensing process of ITER. A little more than one month after being notified that our proposals on the Tokamak’s operational conditions and design fulfilled the French safety requirements, we have now received from the Autorité de Sûreté Nucléaire (ASN)  the draft of the Décret d’Autorisation de Création — the final green light from the French Authorities to create our installation. We are currently analyzing this draft and we will soon send back our comments to ASN. Then, a discussion will be organized with a college of ASN experts and at long last the final decree will be published — hopefully before the end of the year. This is a lengthy, complex, demanding — sometimes frustrating… — process. But I must say it is also a very good process. ITER is the first fusion installation that will receive a full nuclear licence. And this is very important, not only for us here at ITER but for the whole worldwide fusion community. We have always claimed that fusion is safe and in the past two years, we went through an exceptionally strict and challenging process to demonstrate that it is indeed. Now an independent body of experts, with a deserved reputation for being among the „toughest” in the world, is in the process of validating our claim. And again, this is a first: no fusion installation, not even JET or TFTR which, at one point implemented deuterium + tritium fusion, went through this process. Twenty-seven years have passed since President Reagan and Secretary Gorbatchev met in Geneva and laid the ground for the project of an international experimental fusion reactor „for the benefit of all mankind”. We all feel a deep satisfaction in seeing these 27 years of hard work and dedication now converging into a Czytaj dalej...

Common controls in ITER and IFMIF

On the 20th and 21st of August several meetings took place at Rokkasho (Japan) between the CODAC  teams in charge of the machine protection and interlocks of ITER and the International Fusion Materials Irradiation Facility (IFMIF) team. IFMIF is one of the projects of the Broader Approach Agreement between Japan and Europe, which was signed to support ITER and achieve an early realization of Fusion Energy for peaceful purpose. In particular, IFMIF must present results in parallel with ITER operation since these will allow the design of DEMO by qualifying the materials capable to withstand the neutron flux that a commercial nuclear nusion reactor will undergo. The aim of the meetings was to establish a first contact between the controls groups of both „brother” organisations focusing on the development of the machine protection systems. The sessions started with a seminar by Antonio Vergara (ITER) summarising his experience on the design, implementation and commissioning of machine protection systems for high energy physics accelerators like the Large Hadron Collider at CERN and how the lessons learnt can be applied to ITER and IFMIF interlocks. The presentation was followed by a  series of meetings organised by the IFMIF/ Engineering Validation and Engineering Design Activities (EVEDA) Project Leader,  Juan Knaster. IFMIF plant will bombard suitable materials reaching more than 20 displacements per atom (dpa)/year (this value means that in average an atom has been displaced from its lattice 20 times per year). This would allow to obtain within a few years of operation the expected 150 dpa at the end of life of a commercial reactor; and with neutrons at an energy spectrum around the 14 MeV (typical of a Deuterium-Tritium nuclear fusion). The neutron flux will be obtained by accele Czytaj dalej...