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ITER’s fusion reactor just had all 6.8 miles of its cooling pipes cut off and replaced \u2014 not because of a design flaw, but because of chlorine left over from a cleaning bath that nobody caught in time.<\/p>\n
The deepest crack measured barely two millimeters, yet it was enough to ground the entire thermal shield program for three years and pull hardware back out of the assembly pit after it had already gone in.<\/p>\n
This is the kind of cascading consequence that a single overlooked process step can trigger on a 35-nation, multibillion-dollar machine where you simply cannot send someone in with a wrench to fix a coolant leak.<\/p>\n
If you’ve ever wondered why fusion power keeps slipping its schedule, the answer is usually something this specific and this expensive.<\/p>\n
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<\/p>\n Energy<\/p>\n A 142-megawatt hydroelectric plant that made 5 percent of Tasmania\u2019s power burned to its steel frame overnight, investigators have traced the fire to the workshop floor at one end of the turbine hall, and nobody knows yet whether the five turbines survived<\/p>\n 2 hours<\/p>\n <\/a><\/p>\n Energy<\/p>\n A 615-megawatt reactor lost its cooling towers, its transformer and its power lines to a teardown crew, so rebuilding all three to get it on the grid by early 2029 takes up to $1.9 billion in federal money, the biggest check any American restart has drawn<\/p>\n 5 hours<\/p>\n <\/a><\/p>\n Energy<\/p>\n An 850-megawatt battery pushed 700 megawatts into the grid for two straight hours on Friday and then pulled almost 850 back out of it, its second full-power test in three days, nearly eleven months after a transformer failure cut its grid contract in half<\/p>\n 6 hours<\/p>\n <\/a><\/p>\n Energy<\/p>\n A Connecticut city stood 1,920 solar panels on a sealed garbage hill where no steel post can go in, because a driven pile would punch through the lid keeping decades of trash away from the water, so concrete blocks hold every rack down, and the dump now pays city hall $6,000 a month<\/p>\n 21 hours<\/p>\n <\/a>AI-generated summary from reviews, comparisons and articles by AutoNotion<\/p>\n I spent an afternoon once grinding rust off the floor pan of an old car. It threw sparks across the garage, ruined a shirt and left a patch I still wouldn\u2019t show anyone. Crews on the ITER fusion project in southern France have just finished the industrial version of that job. Theirs ran three years and ended with 2,205 pounds of silver on the shop floor.<\/p>\n The ITER Organization<\/a> put the news out on September 7. What they\u2019d been fixing is the vacuum vessel thermal shield, the thin silver skin that sits between the reactor\u2019s plasma chamber and the enormous magnets wrapped around it. Workers stripped 6.8 miles of cooling pipe off the panels, ground the silver coating away, welded new pipe on and polished every surface back to a mirror. The work wrapped up in July, and ITER says the contractor got there ahead of schedule, which isn\u2019t a sentence anyone\u2019s gotten to write about this project very often.<\/p>\n So why is a fusion reactor plated in silver?<\/p>\n Because silver is about the best thing you can put on a panel if you want it to bounce heat radiation instead of soaking it up. The superconducting magnets behind that shield run at 4 kelvin, which is minus 452 degrees Fahrenheit, and every stray watt that reaches them has to be hauled back out by the cryogenic plant. So the shield has one job, and that\u2019s stopping heat before it arrives.<\/p>\n It isn\u2019t a slab of silver, in case you\u2019re picturing one. The panels are steel, about three-quarters of an inch thick, with silver plating on the surface and small pipes welded all over them carrying cold helium gas. There\u2019s roughly 14 miles of that pipework welded onto the panels in total, and this repair program accounted for 6.8 of those miles.<\/p>\n So what was chlorine doing anywhere near a machine like that?<\/p>\n The cracks started in a cleaning bath<\/p>\n Before the panels get their silver, they go through a hydrochloric acid wash and a nickel coat. That chlorine wasn\u2019t supposed to stay there. ITER says some of it didn\u2019t wash back out and got trapped in small pockets near the welds that hold the cooling pipes on. Bending and welding those pipes left stress in the metal, the leftover chlorine worked on it slowly, and what you\u2019re left with is a failure mode called stress corrosion cracking. The steel doesn\u2019t rust away anywhere you can see it. It splits.<\/p>\n Helium leak tests in November 2021 turned it up in three panels that hadn\u2019t even been installed yet. The deepest crack ITER measured ran 0.09 inch, a hair over two millimeters, and went clear across the width of the pipe wall. You can\u2019t get at a coolant leak inside a sealed tokamak with a wrench, so the project assumed every pipe was suspect and committed to replacing all of them<\/a>. That decision also meant pulling a module back out of the assembly pit after it had already gone in, which is about as unwelcome a call as a construction project ever has to make.<\/p>\n The panels came back polished instead of plated<\/p>\n Grinding the silver off is deliberate. The machining takes the coating plus a sliver of the steel under the old pipe path, so the contaminated layer leaves with it and there\u2019s no chlorine rinse to do afterward. New pipe gets bent and welded on. Then the panel is polished until it\u2019s a mirror<\/a>, which brings back the low emissivity the plating used to provide. For a problem the plating process caused in the first place, that\u2019s a fairly elegant way out.<\/p>\n Autonoci\u00f3n Newsletter<\/p>\n No spam. Unsubscribe anytime. Privacy policy (opens in new window)<\/a><\/p>\n ITER\u2019s September note doesn\u2019t put a cost on the three-year program, and it doesn\u2019t spell out how the rest of the shield\u2019s pipework was handled. I\u2019d rather tell you that than guess at it.<\/p>\n Silver removed<\/p>\n 2,205 lb<\/p>\n Coating ground off the shield panels so the trapped chlorine left with it.<\/p>\n Cooling pipe cut out<\/p>\n 6.8 miles<\/p>\n Out of roughly 14 miles welded onto the thermal shield panels in total.<\/p>\n Deepest crack<\/p>\n 0.09 in<\/p>\n Measured at 2.2 millimeters, across the full width of a pipe wall.<\/p>\n Repair program<\/p>\n 3 years<\/p>\n Launched in 2023, finished this July, carried out by contractor INOX-CVA.<\/p>\n The rest of the machine didn\u2019t wait around<\/p>\n Sector module #1 went into the pit at the end of July, the sixth of nine wedges that make up the plasma chamber. We wrote about that 30-hour lift, which landed almost six months early<\/a>, when it happened. That\u2019s two-thirds of the chamber standing in the ground now. Three vacuum vessel sectors are sitting on their own gravity supports, and once sector #5 was transferred in August the teams judged the arrangement steady enough to start preparing for the welding that turns nine wedges into one ring.<\/p>\n Bellows installation started too. There are 93 of them in the design, they connect the vacuum vessel to the cryostat and the cryostat to the building, and they\u2019re in there because the chamber moves up to an inch in any direction as it heats up and cools down. Five sets are bolted in and several are already being welded. That\u2019s five out of 93. The welding program that includes those bellows is scheduled to run five years, and I don\u2019t think anyone expects that number to shrink.<\/p>\n Sector #3 was handed over to the assembly teams on September 2 after a summer of bevel repairs, which closes out a three-year campaign on the sector edges that get welded to their neighbors. It also carries 120 sensors for reading magnetic field once the machine runs, which puts it among the more heavily wired sectors of the nine.<\/p>\n A 364-ton magnet is next in line for 34,000 amps<\/p>\n ITER also runs a magnet cold test facility on the site, which it says is the biggest superconducting magnet test bench anywhere. The idea behind it isn\u2019t complicated. You chill a finished coil down to 4 kelvin, push current through it and find out how it behaves before anyone lowers it into the machine. You\u2019d much rather turn up a bad joint on a test stand than in the pit.<\/p>\n The coils on that bench are the toroidal field magnets, the D-shaped ones that bolt onto the flanks of each sector. They\u2019re a different animal from the central solenoid, the column of magnet that stands in the middle of the machine and got its final module in June<\/a>.<\/p>\n Testing began in May, when toroidal field coil #7 went down to 4 kelvin and took 10,000 amps. Engineers reworked the electrical system for higher current after that and installed coil #17, which got cold in about 10 days.<\/p>\n