France runs a bigger share of its grid on nuclear power than any other country, around 70 percent in a normal year, and the rest of the world treats its fleet as the reference design. What that fleet had stopped doing was growing. The last new reactor France finished, Civaux 2, entered service in April 2002, which means the youngest machine in the famous French fleet was old enough to buy a beer in an American bar.<\/p>\n
That finally changed this spring. On May 5, 2026, Flamanville 3 formally entered commercial operation, and the most powerful machine in French history switched from a test schedule to a billing line.<\/p>\n
The hardware earns it. The core generates roughly 4,300 megawatts of raw heat, the generator pushes 1,650 megawatts of electricity out the door, and the thing converting one into the other is the largest steam turbine ever constructed, spinning at 1,500 rpm a few hundred yards from the English Channel.<\/p>\n
Getting the machine to this point took more than eighteen years and a repair saga that reshaped an industry, and the state auditors’ bill reads 23.7 billion euros against a 3.3 billion quote. The calendar has one more surprise, too. On September 26, the newest reactor in the West goes dark again, for 350 days. That part is in the rulebook.<\/p>\n
Start where the fission happens. The reactor pressure vessel is a forged-steel cylinder 36 feet (11 m) tall and 18 feet (5.5 m) across, weighing more than 425 tons, and lowering it into the reactor building took three full days<\/a> back in January 2014. Britain ran the same maneuver at Hinkley Point C this June, dropping a 551-ton vessel into place with the largest land crane on Earth<\/a>. France did it a decade earlier, with less fanfare and far more paperwork still ahead of it.<\/p>\n Around that vessel sits a double shell of reinforced concrete, 2.6 meters (8.5 feet) of combined wall, engineered to shrug off an aircraft impact, with four independent emergency cooling trains giving the safety systems 300 percent redundancy<\/a>. Underneath is the EPR’s party trick: a core catcher, about 500 tons of ceramic-lined spreading floor covering 1,830 square feet (170 square meters), built to catch and cool the molten core if it ever burned through the vessel. It is an extremely elaborate ashtray for a cigarette nobody intends to light.<\/p>\n The business end is steam. Inside the vessel, 241 fuel assemblies push out roughly 4,300 megawatts of heat, four steam generators installed back in 2015 turn that into steam, and the steam feeds the Arabelle, which Alstom announced in 2006 as “the biggest ever built in the world”<\/a> and which still holds the title. It is rated at 1,750 megawatts at the generator terminals, its last-stage blades are 5.7 feet (1.75 m) long, its exhaust opening covers 155 square meters, and it turns at half speed, 1,500 rpm, because blades that size would tear themselves apart at full grid speed. One of its rotors, a 140-ton forging inside a 600-ton module, produces about 1,100 megawatts on its own, more than most entire power plants.<\/p>\n Then there is the building wrapped around all of it. According to Normandy’s regional development agency<\/a>, the site swallowed 400,000 cubic meters of concrete, about 160 Olympic swimming pools’ worth, plus 50,000 tons of steel framework, roughly five Eiffel Towers, and 1,100 miles (1,800 km) of piping, a pipe run from New York to Orlando. The reactor dome alone weighs 240 tons. All of it exists to boil water very, very carefully.<\/p>\n The first concrete went down in December 2007. The plan was a 54-month build, commercial service in 2012, and a bill of 3.3 billion euros. None of those three things survived contact with the machine.<\/p>\n In 2015, carbon concentration anomalies turned up in the steel of the vessel forged at Le Creusot, dragging the regulator into years of analysis. In 2018, welds on the main secondary system failed to meet spec, and the safety authority eventually ordered eight of them, buried in the containment wall, repaired before startup rather than after. Every fix was a first-of-its-kind operation, and every one moved the date.<\/p>\n Fuel finally went into the vessel between May 8 and May 15, 2024. The core went critical on September 3, 2024, and the machine promptly tripped itself offline the next day, then again on September 17. Grid connection came on December 21, 2024, at 11:48 a.m., with then-CEO Luc R\u00e9mont calling it “a historic moment for the entire nuclear sector.”<\/p>\n 2025 was a staircase: 25 percent power cleared in January, 60 percent in July, 80 percent on November 12, and on December 14 at 11:37 the reactor hit 100 percent of nominal power<\/a> for the first time, the turbine delivering 1,669 megawatts gross in that first full-power run. The startup test program closed on April 26, 2026<\/a>. Commercial entry followed on May 5.<\/p>\n EDF’s own construction figure, the one quoted most often, is 13.2 billion euros in 2015 money, and it deliberately excludes financing. France’s national audit office counts differently: in a report published on January 14, 2025, the Cour des Comptes put the total cost at completion at 23.7 billion in 2023 euros<\/a>, financing included. Call it north of $25 billion, roughly seven times the quote.<\/p>\n The Court also ran the business case, and by its math the electricity would need to sell for about 122 euros per megawatt-hour, at an 85 percent load factor, for the project to clear a 4 percent return. France’s reference price framework for nuclear output from 2026 sits around 70 euros. None of that stops the turbine from spinning. It does explain why every conversation about the EPR eventually turns into a spreadsheet fight.<\/p>\n French regulation requires every reactor to undergo a complete inspection, the Visite Compl\u00e8te 1, within roughly 30 months of first fuel loading. Flamanville 3 loaded fuel in May 2024, so the clock runs out this fall. EDF has set the start date at September 26, 2026, and budgeted 350 days<\/a>.<\/p>\n This is heavy engineering, not a checkup. Around 20,000 separate activities, 200 industrial partners, up to 2,500 people on site at peak, and a primary circuit pressure-tested at 205 bar against the 155 bar it runs at every day.<\/p>\n The headline job is a crane lift worthy of the construction years: the 425-ton vessel gets a new lid. The closure head that came out of the Le Creusot forge with those carbon anomalies is being swapped for a clean replacement, the fix the French regulator demanded back in 2017. If EPR steel drama sounds familiar, it should. It is the same family history that has Britain’s regulator picking through weld indications on the lid of Hinkley Point C’s next vessel<\/a> while it is still being welded in France.<\/p>\n There is one more item on the work order. According to EDF statements reported by Ouest-France, the core will be restructured with reinforced fuel after this first cycle, a preventive fix for neutron flux disturbance at the bottom of the vessel that could otherwise risk fuel rod leakage. So the newest reactor in the West is, legally and deliberately, about to take a gap year. It should return to sustained operation around late 2027, and from then on it gets treated like any other unit in the fleet.<\/p>\n Two weeks ago, EDF published its half-year results for 2026<\/a>: French nuclear output of 189.9 terawatt-hours in the first half, up on last year, feeding a record 51 TWh of French electricity exports. The full-year guidance of 350 to 370 TWh now explicitly includes Flamanville 3. After eighteen years as a construction site, the machine is a line item.<\/p>\n Summer still bit the rest of the fleet. At the height of the June and July heatwaves, three reactors were temporarily shut down and nine ran at reduced power under environmental rules, the same river-temperature story we covered when France idled three river-cooled units because the Garonne was legally too warm<\/a>. Flamanville has a structural advantage there: its cooling water comes from the English Channel, the kind of heat sink that does not show up on July curtailment lists the way inland rivers do.<\/p>\nEighteen years from first concrete to first invoice<\/h2>\n
The auditors did the math, and it is ugly<\/h2>\n
It shuts down again on September 26, and that is the plan<\/h2>\n
What the rest of the fleet did this summer<\/h2>\n