26 Aug 2019 to 09 Sep 2019
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Vacuum technology | Record-breaking sealing performance
The ITER vacuum vessel, its ports and port extensions, and port plugs all provide the vacuum boundary and first safety confinement barrier of the ITER machine. In this context, the leak tightness of the large metallic vacuum seals around the ports is critical. In order to leave nothing to chance, the ITER Organization is testing vacuum sealing on a real-size test rig. Recent test results were excellent. The high-performance vacuum sealing of the ITER vacuum vessel's 50+ large ports is a 'first of a kind' challenge due to the rectangular shape of the ports, their large size, and the need to remove and replace port plugs (large, stainless-steel components that 'plug' the openings and also play a role as structural host to systems such as diagnostics). Eamonn Quinn is responsible officer for the Large Seal Test Rig (LSTR) program. 'To leave nothing to chance, a full-size replica of the largest equatorial ports was designed, manufactured and installed on site with the purpose of testing the vacuum sealing of what will be the largest ports ever built on a tokamak.' The equipment was installed in the European Poloidal Field Coils Winding Facility on site, where the 'clean' conditions were ideal for the tests, and space was made available courtesy of the European Domestic Agency. The test rig is of an impressive size (nearly 5 metres in height and as many in length) and it weighs around 19 tonnes. It gives a preview of how the ITER machine will look when seen through the equatorial ports cells, as they are starting now to take shape on the construction site. It was built and installed by Indian high-tech company Vacuum Techniques. There was much preparation, along with repeated inspections and some anxiety as the first large, double all-metallic seal was positioned on the flange. The flanges were brought together with the repeated tightening of 100 bolts, and after a number of hours of muscle flexing the seals were compressed. Then came the leak tests: first a quick one—no leak found. Then the thorough one, during which the leak rate across each seal was <10-11 Pa.m3.s-1 —a world-record-breaking sealing performance for the largest non-circular all metal vacuum seal! (In lay terms, that means that no more than the volume of air contained in a glass would leak over a period of ... 100 million years.) The performance on this first test was well beyond the requirements, beyond all expectation. In short, a world record breaker! The metal seals were made by Technetics (US). Company Vice President Bob Panza had time to comment: 'I heard the wonderful news yesterday. This is a result of good collaboration between our companies and we should all be proud of the results.' The seal test rig not only allows the largest demountable rectangular seals to be tested, but also enables us to prepare installation techniques which will be critical to achieving the required vacuum quality. Since the first test, the validation program has successfully continued with heating the flanges to 100 °C and then on to 240 °C and still the sealing performance has been maintained.
Towards DEMO | What will the blanket teach us?
We often hear about the scientific ideas ITER is designed to confirm, but the project also has an important role as a technology demonstrator. The blanket is a perfect example: its design, fabrication and operation will provide important information for the next-step fusion reactor, DEMO. The leader of the ITER Blanket Section, René Raffray, explains. What is the role of the blanket in a fusion device? ITER will maintain temperatures of about 150 million degrees in the plasma and about 4 Kelvin (-269 °C) in the superconducting coils used to provide the magnetic confinement and control of the plasma. The two are separated by a distance of a few metres. This is an incredible situation. Unless there's an advanced civilization somewhere else, it's hard to imagine such a temperature gradient occurring anywhere else in the universe. So right in the middle of one of the hottest places in the universe and one of the coldest places in the universe is our blanket, which surrounds the plasma. The blanket protects the rest of the reactor by absorbing most of the radiative and particle heat fluxes from the hot plasma, as well as by stopping or slowing down most of the neutrons that result from the fusion reactions. In this way, the blanket reduces the heat and neutron loads in the vacuum vessel and ex-vessel components—in particular the cryogenic superconducting coils. In addition to these shielding functions, the blanket also provides a few plasma-specific functions. The plasma-facing surface has been designed to limit the influx of impurities in the plasma through erosion. Impurities can drain a lot of energy from the core of the plasma through radiation, which would cool down and, ultimately, quench the plasma. The plasma-facing surface also serves as a plasma boundary during start up and shutdown. For example, through plasma heating and magnetic control a circular plasma will start on the inboard 'first wall' of the blanket and will then grow and detach from the first wall to adopt within about 10 to 20 seconds the typical elliptical shape of divertor mode operation. Due to the high heat deposition expected during plasma operation, ITER will be the first fusion device with an actively cooled blanket, with pressurized water circulating inside the blanket modules. What were the challenges in designing ITER's first-of-a-kind fusion blanket? The blanket will face high heat fluxes and large electromagnetic loads. In addition, the fact that it interfaces with so many other systems has made its design very challenging. We had to accommodate a number of interface requirements—and sometimes those requirements conflict with one another. For example, because the blanket needs to provide neutron shielding, gaps and cutouts should be avoided or minimized to prevent neutron streaming. At the same time, interfacing systems such as diagnostics require cutouts in the blanket, and their design is facilitated when the gaps and cutouts are larger. We have chosen a modular system, with 440 individual blanket modules covering a plasma-facing surface of about 610 m², attached to the vacuum vessel. Each module consists of a shield block at the back and a plasma-facing first wall panel in the front. As its name indicates, the shield block is fundamentally a steel block used for neutron shielding, but with a number of cut-outs to accommodate many interfaces such as the diagnostics, blanket manifolds and heating system, which often results in rather complex shapes. The first wall faces the plasma and is designed to withstand close to 5 MW/m² (about 10 times higher than the heat fluxes on the space shuttle carbon tiles during re-entry). The first wall panel is attached to the shield block through a central bolt and a system of pads, and is designed for replacement by remote handling. Tiles made of beryllium are used as plasma-facing armor due to its low atomic number and relatively benign impurity effect on the plasma. Because of the high heat flux on the first wall panel, we use a copper alloy substrate under the beryllium to serve as a heat sink, which helps conduct the heat to the cooling channels and keep the temperature of the beryllium at a reasonable level. Austenitic stainless steel 316 is used as structural material for the first wall panels and for the shield blocks. Today, blanket shield blocks are in series fabrication in China and South Korea; key technologies for the plasma-facing first wall are in the qualification phase in Europe, Russia and China; Russia is qualifying blanket connectors (flexible supports, key pads, electrical straps); Europe is procuring the blanket manifolds (bundled cooling pipes); and Japan is advancing the design of the blanket remote handling system. The very fact of designing, fabricating and operating such a unique blanket will provide valuable information on manufacturing feasibility, qualification and test procedures, installation, and repair or replacement. How will the next-stage blanket be different? Similar functions are expected from a DEMO or power plant blanket but there will also be two major new requirements: tritium breeding, and the efficient removal of deposited energy for electricity generation. In the ITER machine, hydrogen isotopes deuterium and tritium will fuse to create a helium nucleus and a neutron, releasing a lot of energy in the process. Deuterium is readily available from seawater, but tritium is rare. ITER will procure the tritium fuel necessary for its operational lifetime from the limited global inventory, but for DEMO and the machines that follow, the successful development of tritium breeding within the blanket is essential. This is achieved by introducing lithium in the blanket, which will react with the neutrons from the fusion reaction to produce tritium. (A neutron multiplier such as beryllium is also used in the blanket to increase the number of neutrons available for such a reaction.) ITER will offer a unique opportunity to test mockups of tritium-breeding blankets (called test blanket modules) in a real fusion environment, and provide valuable information on local tritium breeding. Not only will this information boost the confidence that tritium self-sufficiency can be achieved in later-stage devices, but it will also provide a basis from which one can extrapolate to design DEMO or power plant blankets. A second major difference is that the ITER blanket won't be relied on to efficiently remove deposited power for electricity generation. Instead, the power produced will be captured by cooling water at low temperature (70 °C at inlet)—and not be used for electrical power production. In DEMO and beyond, the power carried by the coolant will be transferred to a power cycle fluid (water/steam for a Rankine cycle, or helium for a Brayton cycle) through a heat exchanger, and a high-temperature coolant will be required for economically acceptable power cycle efficiency. For this reason, ITER's test blanket modules will be tested with their own independent cooling systems using either helium-coolant at 500 °C or water-coolant at pressurized water reactor conditions. ITER will also operate with a choice of blanket materials that is not fully applicable to DEMO, where the neutron fluence (a measure of the total number of fusion neutrons per unit area over the component lifetime) is expected to be about 30 times higher. For instance, higher fluences would swell the austenitic steel 316 chosen for ITER, affecting its structural integrity. A different structural material will be required to operate at these higher temperatures and neutron fluences. At the same time, the aim is to minimize the associated radioactive waste of the structure at its end of life by successfully developing and utilizing low-activation structural materials with much shorter decay half-lives (about 100 years or less). Prime candidates are the newly developed reduced-activation ferritic/martensitc (RAFM) steels that are planned for use in the test blanket module structures. What will we learn from the ITER blanket that has relevance for DEMO and beyond? I would look at this question from a broader perspective. The overall programmatic objective of ITER is to demonstrate the scientific and technological feasibility of fusion energy. While the physics side of this objective tends to be well appreciated, less emphasis is put on the equally important goal of demonstrating the availability, integration and testing of technologies essential for a fusion reactor. In addition to the key physics information, we expect a wide range of DEMO-relevant technology information out of ITER. This is clear for the vacuum vessel and most ex-vessel components and systems, such as the superconducting coils, the cryogenic system, the tritium system, diagnostics systems and the cooling system. For the in-vessel components, in addition to key tritium breeding blanket information to be obtained from the ITER test blanket module program, the following important information will be obtained in a range of technology areas in particular for the blanket and divertor. Blanket and divertor design, manufacturability and operation; First wall and divertor heat fluxes, including first wall shaping and alignment (to the millimetre level) to maintain acceptable heat flux levels and to protect leading edges and penetrations; Plasma-facing component and material behaviour under normal and off-normal conditions including erosion; Neutron shielding performance; Tolerance management for an assembly of components; Assembly and remote handling; Integration of all these components and systems while accommodating interface requirements; Reliability and availability of these fusion systems and components.
Summer works | A new chapter opens
Notice anything? Yes, the giant poster (25 x 50 m) on the temporary wall of the Assembly Hall has been removed. Displaying a cutaway of the ITER Tokamak, it had been installed in June 2016 and, for more than three years, it stood as a reminder of ITER's ambition. Little by little, as the bioshield and Tokamak Complex took shape, most of the poster disappeared from view. Its removal in late August marks a first step in the dismantling process that will see the temporary wall that separates the Assembly Hall from the Tokamak Building removed. The poster's disappearance is just one sign that a new chapter is opening in ITER construction. Throughout the worksite, operations large and small are all heading in the same direction: preparing for the assembly phase that will officially commence in March 2020. Following Newsline's summer recess (there is no such thing as a 'summer recess' on the ITER worksite) the gallery below takes you on a tour of the major operations conducted or initiated in August—from the tallest heights of the Tokamak Building where the first pillars of the crane hall will soon be installed, to the lowest depths of the Tokamak pit where work as delicate as watchmaking is being performed on 5-tonne components.
Image of the week | On the thruway from Hefei to Shanghai
Over the next four years, China will be shipping approximately 100 large components for the magnet feeder system, adding up to 1,600 tonnes of equipment in all. Two "Highly Exceptional Loads" left Shanghai in early August. Feeder assembly is one of the major machine assembly activities, representing just over 11 percent of the total Tokamak machine baseline workload. Thirty-one magnet feeders, distributed either under the machine or over the machine, will transport electrical power and cryogens in to the superconducting central solenoid, toroidal and poloidal field coils, and correction coils. Measuring from 30 to 50 metres in length, the feeders are manufactured and shipped in three fully instrumented segments: the coil termination box (furthest from the machine), the cryostat feedthrough (the part of the feeder that passes through the bioshield and cryostat into the vacuum environment) and the in-cryostat feeder (which connects to the coils). The in-cryostat feeders sent in August by China have a unique semi-circular shape due to their assembly position under the vacuum vessel inside of the cryostat base. They will connect to the bottom correction coils, and need to be on site relatively early in the assembly sequence. The components will travel this month along the ITER Itinerary as "Highly Exceptional Loads.*" *About 10,000 ITER components fall into the category of "Conventional Loads," 3,000 are "Conventional Exceptional Loads" and 300 are "Highly Exceptional Loads."
India | Modi praises ITER at UNESCO
In August, while on official visit to France at the invitation of President Emmanuel Macron, Prime Minister Narendra Modi of India shared his vision of cooperation in the field of energy on several occasions. At the UNESCO headquarters in Paris, he took pride in his country's participation in "the only fusion project under construction in the world." In conversations with the French President, in addressing the G7 Summit, and in bilateral exchanges with other heads of state or of government, he highlighted India's large-scale efforts to develop clean energy, mitigate climate change and achieve most of the COP 21 environmental goals set for 2030 in the coming 18 months. On 23 August, Prime Minister Modi was at the UNESCO headquarters in Paris to address the Indian community in France. 'Many of you,' he said, 'are representing India's scientific talent in France, and are involved in the signature projects of both countries in atomic energy, aerospace technologies and other high-tech areas.' ITER is one of the 'signature projects' that Modi specifically highlighted: 'The only fusion project under construction in the world is in France and India is part of it. A highly capable Indian team is involved in this major scientific venture, one of the most important of this century. When fusion technology becomes available, providing immense quantities of energy for future generations, this achievement will bear the mark of your contribution. Think of the pride that will be felt by every Indian!' The expatriate Indian community has a strong relation 'with the soil of India.' With France, the relation is also strong but of a different nature. 'It is one of hard work and dedication,' said the Indian Prime Minister, 'and your efforts, your successes are a matter of pride for both France and India.'
ITER Organization 2018 Financial Report
ITER Organization 2018 Annual Report
A history of fusion research and development Part 3
"Sol artificial": como a fusão nuclear poderá impactar o futuro energético?
National Nuclear Center Prepares for Second Launch of 'Tokamak' Reactor
Department of Energy to Provide $50 Million for Fusion Energy and Plasma Science Research
In Making Of A Miniature Sun On Earth, India's Contribution Is Enormous (video 14'33")
"Made In India" Written All Over "Little Sun" Being Created In France (includes video report, 3'02")