07 Sep 2020 to 14 Sep 2020
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Vacuum vessel | Sector #6 is leak tight
The first ITER vacuum vessel sector has passed a helium leak test on site with flying colours. Back in March 2020, as experts from the Korean Domestic Agency and Hyundai Heavy Industries were carrying out final quality control evaluations, vacuum vessel sector #6 was subjected to a series of factory acceptance tests, which it passed successfully. The most critical of these—the helium leak test—is a way to ensure at the end of the manufacturing process that no leaks in the many welds in a vacuum vessel sector have been overlooked or allowed to pass, and it demonstrates the absolute leak tightness of the component. In a typical year, an observer/quality control inspector from the ITER Organization as well as an inspector from the Agreed Notified Body (authorized by the French Nuclear Regulator ASN to assess the conformity of components in the pressure equipment category) would have been present for the tests in Korea. But because these visits were rendered impossible by COVID-19 travel restrictions—and not wanting to delay the shipment of the component—it was agreed that acceptance activities would be split between Hyundai Heavy Industries and the ITER Organization ,with Hyundai responsible for demonstrating the safety leak rate requirement at the company's premises and the ITER Organization responsible for the more stringent operational leak rate requirement as part of acceptance tests on site. On 2 September, approximately one month after the component's arrival, the ITER vacuum team enclosed the 440-tonne vacuum vessel sector in a plastic bag filled with 100 cubic metres of helium gas—or the equivalent of 10,000 party balloons—while pumping the sector's interspace to create a vacuum. As helium—the second lightest element—can pass through any crack in the vessel boundaries, no matter how small, any presence of helium in the interspace would be detected by the leak detection system based on ultra-sensitive mass spectrometry. The result was completely successful, with no leaks above the limit of detection found. Vacuum vessel sector #6 is confirmed to leak tight to 10-10 Pam³s-1, which is two orders of magnitude tighter than the acceptance criteria. The test was carried out with the Agreed Notified Body inspector as witness. 'This is a major achievement,' says Liam Worth of the Vacuum Design and Delivery Section. 'Normally to reach this leak test sensitivity one would expect to bake the vacuum vessel sector to condition the interspace for the test. However for the sector #6 baking was not required as the stringent cleanliness requirements of the shield blocks installed in the interspace have been respected—this is good news as it is likely that other sectors will not require baking either, thus saving time and money.' The test protocol for vacuum vessel leak testing, as well as the equipment, was developed by the ITER vacuum team. (See more here). 'The idea of performing the leak test in this way was first proposed some 14 years ago and we have been refining the procedure through test qualifications since,' says Robert Pearce, Vacuum and Design and Installation Section Leader. 'We are all looking forward to repeat test successes as the other sectors are manufactured and delivered.'
Vacuum vessel | India completes in-wall shielding package
The Indian Domestic Agency has completed the procurement of about 9,000 in-wall shielding blocks and accompanying support ribs, brackets and fasteners. The majority of these elements have been delivered to the contractors manufacturing the ITER vacuum vessel in Europe and Korea. In the space between the inner and outer shells of the ITER vacuum vessel are tightly sandwiched stacks of borated or ferromagnetic steel blocks that serve a double purpose: shielding components outside of the vessel from fusion neutrons and helping to optimize plasma performance by reducing toroidal field ripple. The Indian Domestic Agency has been in charge of the procurement and delivery of approximately 9,000 shielding blocks, mainly for installation into the vacuum vessel sectors during the fabrication process in Korea and Europe. (About 10 percent of the blocks will be delivered to ITER for installation in the field joint regions when the vacuum vessel sectors are assembled in the Tokamak pit.) The weight of each neutron shielding plate can vary between 50 and 500 kg depending on its shape and location. Manufacturing, which was carried out at M/s Avasarala Technologies Limited (ATL), Bengaluru, and Larsen & Toubro (L&T), Surat, required various industrial processes like water jet cutting, precision machining, assembly with tight tolerances, accurate dimensional measurements, spot welding, full penetration welding, and non-destructive testing. 'The design, manufacturing, and installation were challenging because of the variety of design configurations and the tight tolerance requirements,' explains Chang Ho Choi, head of the Sector Modules Delivery & Assembly Division at ITER and leader of the Vacuum Vessel Project Team. 'Thanks to very constructive collaboration between the Domestic Agencies of India, Europe, and Korea and their industries, we have overcome the challenges. Almost 50 percent of the installation of in-wall shielding into the sectors has been completed and the first factory and site acceptance tests (on sector #6) have demonstrated that the quality of the in-wall shielding is quite good.' Read a full report on the ITER India website.
Image of the week | Feeders for the coils
One by one, whether large or small, the elements of the system that delivers electrical power, cryogenic fluids and instrumentation to the ITER magnets are arriving on site from China. On 10 September, two large high-tech components were delivered for the magnet feeder system—one in-cryostat feeder for a bottom correction coil and one feeder ring for a side correction coil. Weighing 4 tonnes and 3 tonnes respectively and measuring 16 and 18 metres in diameter, the two half rings are part of a wave of deliveries from China that, once complete, will amount to a total of 1,600 tonnes of equipment.
Busbar installation | "Power cords" thicker than train rails
Connecting an electrical device to a power source requires an extension cord, generally made of stranded copper wire. Depending on the required current intensity—are you plugging in a bedside lamp, a washing machine or an arc welder?—the cord's section ranges from a few millimetres to more than one centimetre. In the ITER magnet system, where huge components need to be fed with intense DC current, the equivalent of the electrical cord is a 'busbar.' The largest ITER busbars are thicker than a train rail and can carry current 7,000 times more intense than a heavy-duty electrical cable. Busbars are steel-jacketed aluminium bars actively cooled by a constant flow of pressurized water. There will be close to five kilometres of DC busbars—amounting to 500 tonnes of material—in the ITER installation, all procured by Russia. The busbar network originates in the twin Magnet Power Conversion buildings, where AC current from the grid is converted into DC current suitable for the magnet system. The canary-yellow-lacquered bars exit the buildings through 'mezzanines' and pass over two 50-metre-long bridges to the Tokamak Building, where they snake under the ceiling to reach their hungry 'clients': the machine's 18 toroidal field coils, 6 poloidal field coils, 18 correction coils and 6 central solenoid modules, plus the switching network unit for the initial plasma boost and the fast discharge unit that will deal with possible quench events. In the twin Magnet Power Conversion buildings, the installation of approximatively 1.25 kilometres of busbars is almost complete. The focus now is on the Diagnostics Building's basement level (B2) where teams are busy bolting busbars to their supports anchored in the ceiling. Busbars at the basement level are for all 18 toroidal field coils, which are connected in series, poloidal field coils # 4, 5 and 6, the three lower modules of the central solenoid and a set of side and bottom correction coils. In an environment already crowded with cable trays and all sorts of piping and HVAC ducts, the task is particularly challenging: individual busbar segments are sometimes very long (up to 12 metres) and quite heavy, ranging from 2 to 4 tonnes in weight. Moving and adjusting the beams into position is a delicate operation that requires the coordinated movements of forklifts and pulley systems before they can be manually bolted to their support. Once in place, the busbars need to be connected to one another and to cooling water collectors, and hose connections must be installed before the whole system can be tested and commissioned using dummy coils. Busbar installation in the Diagnostics Building began a little more than two weeks ago and is now approximately 20 percent complete. In 2021, similar operations will be performed at the third floor of the Tokamak Building (L3) to connect another set of poloidal field coils, central solenoid modules and correction coils.
Manufacturing | The next sector in line
Thanks to the experience acquired during the fabrication of the first production unit of the vacuum vessel, the Korean Domestic Agency and contractor Hyundai Heavy Industries are advancing the production of three other sectors. The delivery of vacuum vessel sector #6 in early August was celebrated across the ITER community as the culmination of a decade-long industrial adventure. The first-of-series of any complex and unique component is always the most fraught with uncertainty and unexpected challenges. The entire process in Korea—the careful planning, documentation, manufacturing and testing of the first ITER vacuum vessel sector—is now paying dividends as work on the next three sectors is advancing at pace due to the lessons learned. Sector #7, pictured here, is 95% complete at Hyundai Heavy Industries and will be the next sector shipped to ITER. Two other sectors are 82% and 89% finalized. Five other sectors are in fabrication in Europe.
Port stubs: Russian deliveries continue
On August 28, two upper port extensions procured by the Russian Domestic Agency arrived at the South Korean port of Busan. Each of the vacuum vessel's 44 openings will have custom-made "extensions" to create the junction to the surrounding cryostat. The first link in the two-part chain—the port stub extension—will be welded to the vacuum vessel sectors before they are shipped from their manufacturing locations; (the second, port extensions, will be added during assembly on site). Responsible for the 18 upper ports, the Russian Domestic Agency has been delivering upper port stub extensions to vacuum vessel manufacturers in Korea and Europe since 2017. They are procured under the general contracting responsibility of JSC NIIEFA (part of Rosatom State Corporation), and manufactured by MAN Energy Solutions, Germany. Upper port extensions #14 and #16 were delivered to Korea late August after a one-month sea voyage. The timely delivery of all port stub extensions is critical for the on-time fabrication of vacuum vessel sectors, and thus the overall ITER schedule.
Vladimir Sergeevich Voitsenya, 1935-2020
The ITER community was saddened to learn that Vladimir Sergeevich Voitsenya, a Ukrainian physicist, researcher, and Fellow of the Ukrainian Physical Society, passed away in August 2020. Trained as a Doctor of Science in Physics and Mathematics, he spent much of his career at the Kharkov Institute of Physics and Technology, KhIPT, moving from laboratory head to leading research scientist, head of the plasma diagnostics laboratory, and finally head of the Stellarators Division. Dr Voitsenya's scientific interests included magnetic plasma confinement, plasma-surface interaction, and plasma-facing mirrors for the diagnostics in ITER. 'Vladimir was a key player in the mirror program for ITER diagnostics and indeed his work is the foundation of the current excellent progress in this area,' commented Michael Walsh, Head of ITER Diagnostics. Colleagues at the International Tokamak Physics Activity (ITPA*) remember him for his enthusiasm, his visionary papers, his ideas—many of which are now implemented in ITER diagnostics—and his kind and friendly attitude. "For us he was a diagnostic pioneer, one of the founders and strongest proponents of the ITPA." *The International Tokamak Physics Activity (ITPA) provides a framework for internationally coordinated fusion research activities.
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