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ITER update.

ITER Divertor Design Review

Recently, the ITER Organization concluded the Final Design Review for a full-tungsten ITER divertor. The three-day assessment was the culmination of eighteen months of design, analysis, testing and development on the readiness and the feasibility of a full-tungsten variant capable of withstanding the extreme conditions in ITER.

A comprehensive investigation had been launched in 2011--the Tungsten Divertor Qualification Pro-gram--in consultation with the procuring Domestic Agencies in Russia, Europe and Japan. The program comprised full-scale prototype manufacturing and testing. Challenges related to the specific nature of tungsten were identified and dealt with. "The completed design now requires some refinement with respect to the local shaping of the tungsten monoblocks," said Philippe Mertens from the Research Centre in Juelich, Germany, who chaired the review.

ITER Test Blanket Design Review

Recently, the ITER project, and the worldwide fusion community, held the first conceptual design review within the Test Blanket Module (TBM) program, a key technology development paving the way to fusion power. It was not yet the turn of the tritium-breeding test modules to be assessed, but that of the components required for hosting them.

During its operational phase, ITER will draw upon the global (civil) inventory of tritium, currently estimated at 20 kilos. But future fusion power stations would have to create their own supply of tritium. Part of ITER's mission is to test different tritium breeding concepts proposed and developed by the Members--concepts that will enable future fusion reactors to produce their fuel within the machine (tritium self-sufficiency) and at the same time extract the heat produced by the fusion reaction and convert it into electricity.

While six different tritium breeding concepts--the Test Blanket Modules--are currently in their pre-conceptual design phase, a group of experts lead by ITER Senior Engineer Guenter Janeschitz concluded the first design check of the modules' frames and housings, as Well as the dummy modules that Will be needed to substitute for the actual TBM sets in order to close and seal the port plugs in the case of delayed delivery or in case replacement is required. Mario Merola, in charge of ITER's in-vessel components, called the design review "a significant step forward toward the goal of testing tritium breeding technology."

Delivery and installation of six Test Blanket Systems is planned during the machine's first shutdown period following First Plasma.

Toroidal Superconductor Strand Procurment

"Toroidal field strand procurement is going rather well," reports Arnaud Devred, who heads the Superconductor Systems & Auxiliaries Section at ITER. "We are on schedule."

Manufactured by suppliers in six ITER Domestic Agencies--China, Europe, Japan, Korea, Russia and the USA--production of niobium-tin (Nb3Sn) superconducting strand for ITER's toroidal field coils began in 2009 and has now topped 400 tons. That's more than 80,000 kilometres of strand--enough to go around the world twice at the Equator. Worldwide capacity has had to ramp up significantly to meet the Project's demand. There are eight qualified suppliers for ITER, including three that are new to the market (one in China, one in Korea and one in Russia). In 2011 and 2012, these eight suppliers, together, turned out over 100 tons annually. "One hundred tons per annum represents a spectacular increase in the worldwide production of this multifilament wire which was estimated, before ITR production, at a maximum of 15 tons per year," says Devred.

Eighteen toroidal field coils will be produced for ITER plus a nineteenth (a spare). That's approximately 420 tons of strand, give or take a bit of spare material planned by each Domestic Agency. The production curve will begin to flatten in 2013 as contracts are brought to a close in several Domestic Agencies.

Devred estimates the market value of the toroidal field strand procurement at over EUR 200 million. "It has been very satisfying to see this procurement unfold and to watch our international collaboration develop at every step in the process," says Devred. "In addition to the sheer scale of this procurement, what is also remarkable is the quality control and quality assurance that we have been able to set into place."

ITER Scientific Collaborations

As was foreseen by the authors of the ITER Agreement, signed in 2006 by the seven ITER Members, the ITER Organization may conclude scientific collaboration agreements with other international organizations and institutions in the interest of promoting cooperation on fusion as an energy source. For ITER, collaboration agreements keep ITER scientists and engineers in close touch with work going on in precise domains relating to fusion science and technology; for the laboratories and institutes, they are an opportunity to collaborate with the fusion community's most advanced experiment.

Since January 2008, the ITER Organization has signed 34 scientific collaboration agreements and another 4 are currently in the preparatory stages. A common thread amongst these agreements is the training of young researchers. "In the coming years, I envision more and more of this type of scientific exchange for the ITER Organization," says the Director-General of the ITER Organization, Osamu Motojima. "I would like to open ITER's door to younger people who will in fact take on a lot of the responsibility for fusion in the future. ITER will be the foremost research laboratory for magnetic fusion. Scientific collaboration agreements enrich the experience of our scientists, and provide training for the next generation of fusion scientists. The ITER Organization is a Centre of Excellence in this area."

Under these scientific collaboration agreements, the ITER Organization and research institutes can cooperate in academic and scientific fields of mutual interest. "Some of the ideas for collaboration come from our scientists. We have compiled a database of agreements signed by the ITER Organization so that when we're approached, we can inform them whether we already have an agreement with the institute in question," says Anna Tyler of Legal Affairs. Typically, the agreements cover the following type of collaboration: joint supervision of students working on Master's or PhD theses; joint training and exchange of young scientists, engineers, interns and experts; joint research projects (particularly in plasma physics); and joint seminars. Collaboration agreements have been signed with laboratories and institutes in Austria, China France, Germany, India, Italy, Japan, Korea, Monaco, the Netherlands, Spain, Switzerland, Japan, and the UK--the most recent to date was signed just last month with the Department of Civil and Industrial Engineering at the University of Pisa (Italy).

David Campbell, head of ITER Plasma Operation Directorate, has been able to see the practical benefits of such exchanges. "Because we are aiming to develop ITER as centre of excellence in fusion research, such agreements allow us to develop scientific and technology exchanges with leading fusion research institutions around the world, building a network of fusion research activities which not only supports the preparations for ITER operation, but also contributes to the longer-term realization of the potential of fusion energy.

Superconducting Magnet Quench System

A robust detection system is under development to protect the ITER superconducting magnets in case of quenches--those events in a magnet's lifetime when superconductivity is lost and the conductors return to a resistive state. Superconductivity can be maintained as long as certain thresholds conditions are respected (cryogenic temperatures, current density, magnetic field). Outside of these boundary conditions a magnet will return to its normal resistive state and the high current will produce high heat and voltage. This transition from superconducting to resistive is referred to as a quench.

During a quench, temperature, voltage and mechanical stresses increase--not only on the coil itself, but also in the magnet feeders and the magnet structures. A quench that begins in one part of a superconducting coil can propagate, causing other areas to lose their superconductivity. As this phenomenon builds, it is essential to discharge the huge energy accumulated in the magnet to the exterior of the Tokamak Building.

Magnet quenches aren't expected often during the lifetime of ITER, but it is necessary to plan for them. "Quenches aren't an accident, failure or defect--they are part of the life of a, superconducting magnet and the latter must be designed to withstand them," says Felix Rodriguez-Mateos, the quench detection responsible engineer in the Magnet Division. "It is our job to equip ITER with a detection system so that when a quench occurs we react rapidly to protect the integrity of the coils." "A quench is not an off-normal event," confirms Neil Mitchell, head of the Magnet Division. "But we need a robust detection system to protect our magnets, avoid unnecessary machine downtime, and also as a safety function to discharge large stored energy and avoid damage to the first confinement barrier--the vacuum vessel."

Quench management will be a two-fold strategy in ITER: first quench detection, then magnet energy extraction. The time between detection and action has to be short enough to limit the temperature increase in the coil and avoid any damage. "We have on the order of 2-3 seconds to detect a quench and act," says Felix. The primary detection system--called the investment protection quench detection system--will monitor the resistive voltage of the superconducting coils (there is also a secondary detection system). Why the voltage? "Whereas during superconducting operation the resistive voltage in a coil is practically zero, a quench would cause it to begin to climb," explains Felix. "By comparing voltage drops at two symmetric windings for instance, the instruments will detect variations of only fractions of a volt." Above a threshold level, these variations trigger a signal that is sent to the central interlock control system. In order to avoid unnecessary machine downtime, specific signal processing is required within the quench detection system to discriminate the resistive voltage from the 'inductive one due to the variations of the magnetic field--that is, to distinguish "true" signals from "false."

"The Tokamak environment will be a very noisy one for our instruments--that's one of the challenges of quench detection in ITER," says Felix. "The difficulty will be to cull out false triggers while at the same time not allowing a real quench to go undetected," says Felix. "We have tried to build enough redundancy into the system so as to minimize false signals. We don't want to discharge the coils and lose machine availability if we don't have to." If a quench is confirmed, the switches on large resistors connecting coil and resistors are thrown open and the magnetic energy of the coil is rapidly dissipated, avoiding any damage to the coils. For the toroidal field coils that have the largest amount of stored energy, 41 GJ, achieving total discharge can take about one and a half minutes.

To detect the start of a quench in any part of the magnet system, voltage measuring instruments (over 3,000 sensors) will be integrated at regular distances onto ITER's coils, feeding bus bars, and current leads. Following the Manufacturing Readiness Review for coil instrumentation last December, the Magnet Division is currently in the phase of preparing over 20 individual tenders (~EUR 25 million). The instruments imply a variety of components and technologies to compensate inductive signals. Much process and material development has gone into the design of these systems.

In addition, an R&D collaboration has been underway at the superconducting Korean tokamak KSTAR since 2009 to learn more about compensating the electromagnetic fields. ITER is collaborating with the KSTAR magnet team to gather information on the electromagnetic signals picked up by the superconducting cables during plasma disruptions. This data will assist the ITER team in designing compensation systems to separate the electromagnetic noise of a disruption from a quench.

"Quench detection in ITER is the most challenging around," concludes Felix, who has approximately 25 years of experience in the field. "At the Large Hadron Collider (LHC), for instance, we were working with faster detection times. But in ITER, there will be a tremendous amount of interference for the instruments to sort through--electromagnetic noise, swinging voltages, couplings, perturbations. At ITER, we are also dealing with higher current, bigger common mode voltages, and larger stored energy. We'll be pushing quench detection and protection to the limit of technology today."

Cooling System Drain Tank

Drain tank fabrication for ITER's tokamak cooling water system is progressing steadily under the leadership of US ITER, which is managed by Oak Ridge National Laboratory for the US Department of Energy. The drain tanks will be among the first major hardware items shipped to the ITER site in France. The US production timing will accommodate the installation sequence for the ITER fusion facility.

Joseph Oat Corporation, a sub-contractor to AREVA Federal Services based in Camden, New Jersey, has begun fabrication activities for four 10-metre-tall, 78 metric ton drain tanks and one 5-metre-tall, 46 metric ton drain tank. Another industry partner, ODOM Industries in Milford, Ohio, is fabricating the ten tank heads as a sub-contractor to the Joseph Oat Corporation. ODOM will ship each tank head as it is fabricated, and will complete delivery to Joseph Oat Corporation by the end of 2013. Joseph Oat, which specializes in industrial fabrication of pressure vessels and heat exchange technologies, expects to stagger completion of drain tanks throughout the summer and fall of 2014.

"Because the tanks are so large, the ITER Organization will install the tanks one at a time and do so before the neighboring building is constructed," Chris Beatty, US ITER tokamak cooling water systems engineer, said. Beatty noted that the Hot Cell building will permanently block access to the drain tanks in the Tokamak Complex once the ITER facility is complete. The tanks, which are built to last 40 years, are expected to perform beyond the duration of the ITER project. The pressurized, stainless steel drain tanks must meet French regulations, giving these US fabricators the opportunity to gain experience implementing French regulations for nuclear pressure equipment. "Compliance with French nuclear pressure equipment regulations is new to most manufacturers in the US," says Glen Cowart, US ITER quality assurance specialist. "In addition, tank fabrication must meet the ITER Organization's requirements as well as engineering and quality criteria established by ARE VA Federal Services and US ITER."

Neutral Beam Port Shielding

The Korean Domestic Agency signed an important contract in July for the fabrication of neutral beam port in-wall shielding with Korean supplier Hyundai Heavy Industries Co., LTD (HHI). Through this contract, installation of the in-wall shielding into the port stub extensions will begin in mid-2015 with fabrication completed by early 2016. Hyundai Heavy Industries is also manufacturing two sectors of the ITER vacuum vessel as contractor to the Korean Domestic Agency, as well as seventeen equatorial ports and the nine lower ports. The vacuum vessel's neutral beam ports are composed of a connecting duct, port extension, and port stub extension. The main purpose of in-wall shielding is to provide neutron shielding for the superconducting magnets, the thermal shield and the cryostat.

Toroidal Field Coil Prototype

The first step in the fabrication of the full-size, superconducting prototype of a toroidal field coil double pancake has been successfully carried out in Europe. Winding was completed at the beginning of August at the ASG premises in La Spezia, Italy. The European Domestic Agency, Fusion for Energy, is responsible for procuring ten toroidal field coils (and Japan, nine). These D-shaped coils will be operated with an electrical current of 68,000 amps in order to produce the magnetic field that confines and holds the plasma in place. Toroidal field coils will weigh approximately 300 tons, and measure 16.5 m in height and 9.5 m in width.

Each one of ITER's toroidal field coils will contain seven double pancakes. These double pancakes are composed of a length of superconductor, which carries the electrical current, and a stainless steel D-shaped plate called a radial plate, which holds and mechanically supports the conductor through groves machined on both sides along a spiral trajectory.

For the European commitments to ITER, a consortium made up of ASG (Italy), Iberdrola (Spain) and Elytt (Spain) will manufacture the full-size, superconducting prototype as well as the production toroidal field coil double pancakes in the future.

Diagnostics

A significant Procurement Arrangement was concluded recently between the ITER Organization and the Japanese Domestic Agency for four key diagnostic systems for ITER.

The Divertor Impurity Monitor is a window to the operation of the divertor, monitoring impurity flows and allowing the optimization of operation. Divertor Thermography gives a detailed view of the heat load profile of the divertor targets--a key diagnostic for the protection of divertor components. Edge Thomson Scattering is used to measure the temperature and density profile of the edge of the ITER plasma, providing useful information in the study of the confinement properties of the plasma edge and for the optimization of fusion performance. And finally, the Poloidal Polarimeter will measure the plasma current density across the plasma cross-section (the current profile). The details of this profile affect stability and heat transport in the core and must be carefully measured and adjusted to achieve ITER's long pulses.

The signature represents a key milestone for both the Japanese Domestic Agency and the ITER Organization, and an important milestone for the project schedule. The long-distance coordination of the Procurement Arrangement signature went smoothly--the document was first signed by ITER Director-General Motojima, before being transported half way around the world by courier to be signed by T. Oikawa, the Director of International Affairs, Japan Atomic Energy Agency (JAEA).
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Publication:Fusion Power Report
Geographic Code:9JAPA
Date:Sep 1, 2013
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