With the conclusion of the preliminary design review, the ITER cryostat passed another big milestone last week. Following the conceptual design review performed in November 2009, the review panel chaired by Felix Schauer from the Max Planck Institute (IPP) in Garching, Germany, once more went through all the design documents necessary for the Procurement Arrangement and looked at all the interfaces with other machine parts with special focus on in-vessel maintenance issues.
The ITER cryostat will be the world's largest high vacuum chamber. It is a single wall cylindrical vacuum vessel, with a vertical axis, a flat bottom and a tori-spherical top lid. Its internal diameter is about 28 metres, it's height is about 29 metres. It will hold a volume of about 8,500 m³.
Though it has to hold a high vacuum with a pressure of 1x10-4 Pa, the ITER cryostat will have about 200 penetrations in total. Most of them are small and provide the supply of power, water or helium for the in-cryostat components. Twenty-three of the penetrations are slightly larger in order to allow human access for maintenance reasons. The biggest "hole" in the cryostat (10 metres in diameter) is the top lid that can be taken off in case the central solenoid magnet needs to be exchanged.
"The main issue at the preliminary design review was to make sure that all the requirements concerning the design are fulfilled, but also that the enormous amount of interfaces to other components and the outside world are clearly defined," explains Felix Schauer. Naturally, it had also to be checked whether the manufacturing of the components, assembly and later maintenance of the cryostat can be done in a robust way with reasonable effort, and in conformance with all the requirements.
"Even though I come from a large and certainly complex fusion project—the stellarator Wendelstein 7-X in Greifswald, Germany—it was quite impressive when I got in such close contact to the huge ITER cryostat," Schauer comments. "However, the particular challenge for the ITER design as compared to other fusion experiments is not just its size but the fact that it is a nuclear machine and thus everything from design to operation and later decommissioning has to obey corresponding rigorous nuclear regulations."
Since this was a preliminary design review, it is evident that not all detailed questions can be solved at this point. Open issues were lively discussed, and corresponding "chits," i.e., written questions, comments and recommendations, were raised by the members of the meeting. At the end, the review panel came to the conclusion that the cryostat has a sound design and can be built and assembled as it is envisaged. Open issues like completion of some design documents, detailing of interface specifications or special calculations will not significantly influence the design and will be settled before the final design review. Due to the committed and active cooperation of the meeting members, this preliminary design review was a very fruitful event in a pleasant atmosphere.
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The conceptual design review for the coil power supply system was successfully conducted this week. The review panel was made up of 21 persons including members from the ITER Organization, the Domestic Agencies, other fusion and accelerator labs worldwide, and industry.
The purpose of the coil power supply system is to supply all electrical power to the ITER magnets and heating and current drive systems. In addition it must discharge the stored energy in the ITER magnets in case of quench—and this is quite a challenge, as the energy stored in the toroidal field coils, for example, at the maximum (68 kA) current is about 41 GJ.
The system will be the largest ever built, far exceeding prior installations at TFTR, JET, and JT-60 in terms of power and energy. In-kind contributions are made by China and Korea for the AC/DC converters, the reactive power compensation and the AC distribution. The Russian Domestic Agency supplies the switching networks and the fast discharge units.
While many chits were generated, the general opinion of the review committee was that the conceptual design has been well established and that the next phase of the work, the preparation of Procurement Arrangements, can proceed.
"Fusion is the future, and the future is in your hands." This was the message to students and junior scientists from around the world who had gathered recently at the University of Texas to attend the first ITER International Summer School (IISS) to be held in the United States.
Juan Sanchez, the university's Vice President for Research, presented the message to students during the IISS "Texas Barbecue Banquet." The purpose of IISS, held this year from 31 May to 4 June, is to educate young scientists and students on the issues related to the physics and engineering of the ITER experiment.
Host for the IISS was the Institute for Fusion Studies, a national center for theoretical research in plasma physics and fusion energy science. The institute's director, James Van Dam, also heads the US Burning Plasma Organization ( USBPO), which helps coordinate the participation of the US fusion community in the ITER Project.
Three scientists from the institute were among the 20 IISS lecturers, representing seven countries and the ITER Organization. Entitled "Magnetohydrodynamics and Plasma Control in Magnetic Fusion Devices," this year's IISS was attended by 133 participants from 48 institutions representing 17 countries.
For the first time, the IISS offered a workshop where students designed a plasma control system using commercial computational design tools. Because of the difficulty of achieving conditions necessary for the fusion reaction, control systems play a central role in sustaining the reaction and allowing the goals of the experiment to be achieved.
School sponsors for 2010 were the Commissariat à l'Énergie Atomique Cadarache; Embassy of France to the United States; ITER Organization; National Instruments Corporation; Université de Provence; University of Texas; USBPO; and US Department of Energy. Representatives at the school's opening ceremony included Gary Johnson, Deputy Director-General, ITER Tokamak Department, who read written greetings from Director-General Kaname Ikeda; Richard Hazeltine, Physics Department Chairman, University of Texas; and James Truchard, CEO and President of National Instruments.
The theme for next year's school is "Energetic Particles in Magnetic Confinement Systems." It will be held June 6-10 in Aix-en-Provence, France.
Japan was the first Domestic Agency to sign a Procurement Arrangement with the ITER Organization. The Procurement Arrangement for the conductor for the toroidal field magnets was signed in November 2007, and since then Japan has been at the forefront of toroidal field conductor production. As of today, the two Japanese firms Jastec and Hitachi Cable have produced more than 50 tonnes of niobium-tin (Nb3Sn) superconducting strands.
Hitachi Cable has cabled more than 3.8 kilometres of toroidal field cables. In addition to several qualification unit lengths, Nippon Steel Engineering has completed the manufacture of 4 x 430-metre conductor unit lengths that will be used for the winding of side double pancakes. It is getting ready to jacket its first 780-metre conductor unit length that will be used for the winding of a regular double pancake. The four-side double pancake unit lengths are the first ITER Tokamak components to be completed.
From June 8-11, Gary Johnson, Head of the Tokamak Department, led a delegation of ITER Organization experts visiting the Japanese Atomic Energy Agency (JAEA) and the various suppliers involved in toroidal field conductor production. "It is very important at this stage of the project to acknowledge and support the efforts of the Domestic Agencies in stepping up their industrial contracts, and it is a significant milestone to see the completion of the first tokamak components. This sends a strong signal to the world that ITER has entered the construction phase and should encourage all the Domestic Agencies to pursue their efforts," said Gary during his visit.
The strands, cables and conductor unit lengths have undergone or are now undergoing acceptance testing at the various suppliers, as well as verification testing at JAEA as required by the Procurement Arrangement. All data are entered into the Conductor Database for validation and checking. The Japanese suppliers have set very high standards in terms of quality and uniformity of production that will be used as a reference for production around the world. Of course, there has been a learning phase, but initial problems were quickly overcome thanks to a tight collaboration between the ITER Organization and JAEA.
Would the youngest Section Leader at the ITER Organization please step forward? Jun Tao, 39, is the newly-appointed Section Leader for Coil Power Supply. He's taken on responsibility for a critical plant system at a critical time; four procurement packages are scheduled to be signed in his Section before year's end, representing approximately160 kIUA of value. "We're a small team working to very tight deadlines," said Jun, during a break from this week's coil power supply conceptual design review. "For this important system, we must deliver a very reliable, deliverable design to the Domestic Agencies involved with procurement. We need to uncover any issues at this stage, before moving on to the next design level. During this week's review, we have received very valuable advice."
The coil power system at ITER will be essential to successful operation, providing power to the ITER magnet coils for plasma initiation and control, and protection for the magnets against quenches. "ITER will be a very unique and challenging system, with many 'firsts,'" stresses Jun. "Fast discharge units capable of continuously carrying and interrupting DC current up to 68 kA at 10kV have never been built before. And ITER's AC/DC conversion plant and reactive power compensation system will among the largest of their kind."
Since his student days in China, Jun admits that he's been fascinated by tokamak power supplies. He earned an undergraduate and Master's degree in power electronics, and completed a PhD on "Power Supplies for Tokamak Systems" before joining the EAST Tokamak project in 1995. At EAST, Jun was responsible for the reactive power compensation system, and saw the development effort through design, procurement, installation and commissioning.
In Garching, Germany, where he was collaborating with the coil power supply team for the ASDEX Upgrade, he learned—with excitement—that China had joined the ITER Project. Jun joined the Chinese Participating Team for ITER, before arriving at Cadarache as power electronic engineer in 2007.
Jun's experience with tokamak coil power supply systems makes him particularly well-suited to the challenges ahead. Can this challenging system be built? "Yes!" says Jun, without hesitation. "The Domestic Agencies involved with this procurement—China, Korea and Russia—all have experience with tokamak coil power supply systems. Together, we'll succeed!"
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A two-day bilateral meeting between representatives of ITER's Fuel Cycle Division and ITER Korea was held in Daejeon, Korea this week to review the requirements to design the storage and delivery system within the Tritium Plant and fuel cycle. The main purpose of this meeting was to compare the merits and demerits of zirconium cobalt (ZrCo) as the hydride material to those of depleted uranium.
Hydrides are materials—metals in this case—that have the capability of chemically absorbing hydrogen (and its isotopes deuterium and tritium) into their metal lattice structure, thereby acting as a very effective pump at room temperature. Metal hydrides typically store hydrogen at densities higher than in liquid hydrogen. In order to recover the hydrogen (or the deuterium tritium fuel) these metal hydrides must be heated, making them a very safe way to store and deliver tritium and therefore will be used for storage instead of tanks which store hydrogen as a gas.
Since the beginning of the engineering activities for ITER in the 1990s the question of the most suitable metal hydride material is controversially discussed among the experts. During the bilateral meeting, the Korean and ITER teams discussed the pro's and con's for the two candidate materials, weighting criteria such as complexity of the components and system design, schedule, costs and additional need for R&D, giving highest priority to safety aspects.
The meeting concluded with a unanimous preference for depleted uranium. Now it is time to come to a decision about the material that should be used as hydride in ITER.
18 May 2010 was a date that the ITER blanket community will remember. Two critically-important "project change requests" (PCR) were accepted for implementation into the Baseline. They were originated by the ITER design review held in 2007 and confirmed by the blanket conceptual design review held in February this year.
PCR-076 addressed the concern that the beryllium-covered blanket first wall panels are unlikely to have sufficient lifetime under transient heat load events over the 20 years of ITER operation, therefore remote handling capability needs to be clearly demonstrated. This also opens the possibility of a full replacement of the first wall panels in the case of a change of armour material if and when decided.
PCR-077 addressed the new blanket design, namely the shaping of the first wall panels to protect the leading edges; the start-up and shut-down to be carried out on the first wall thereby eliminating the two start-up limiters; and the in-situ replacement of the panels. This latter feature also has important implications on the remote handling operations that will be developed to refurbish the blanket modules inside the vessel.
Following these new remote handling requirements, the importance of a realistic demonstration was pointed out to confirm the remote handling feasibility of the recently-developed FW panels. The Blanket Section, in close collaboration with the Remote Handling Section, has selected R&D items to be conducted in 2010-2011, according to technical priority. The identified items will be investigated by the Japanese Domestic Agency (JA-DA), which is responsible for the Procurement Arrangement of blanket remote handling via a Task Agreement specifically issued for this purpose.
The kick-off meeting for this R&D work was held in Naka, Japan, on 9 June, followed by a number of dedicated technical meetings between the ITER Organization and JA-DA. This is a critically important activity for blanket development, which will address specific remote handling issues like the feasibility of positioning the first wall within the limit of planned fabrication tolerance, the alignment of the cooling pipes which must be remotely cut and re-welded, as well as the required welding procedures. This activity is due to be completed in summer 2011.
As part of its commitments in hosting the ITER Project, France has carried out the clearing and the levelling of the construction site, the establishment of the International School in Manosque, and the construction of an itinerary for the transport of heavy components from the port of Fos-sur-Mer to Cadarache. France, as Host country, is now ready to enter a new phase of site preparation work—the construction of the permanent ITER Headquarters; the reinforcement of the 400 kV electricity line; the building of the electricity grid and transport station on the ITER site; and the cooling water network.
Work on Headquarters will start this summer, and will involve approximately 200 people over two years of construction. Reinforcement work on the 400kV electricity line will take one year, beginning mid-2011. Connected to the Tavel/Boutre network, this line, now reserved for the French Tore Supra tokamak, will be doubled and connected to the electricity grid and transport station located on the ITER platform. Work on the transport station will be carried out between mid-2010 and mid-2011. The cooling water network for the ITER installation will be finished by end 2012.
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