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Finland’s second-largest nuclear unit has been quietly running 155 megawatts short of its nameplate capacity for nearly two years, and the part that finally arrived to fix it was immediately put on a shelf instead of installed.<\/p>\n
A rotor spinning 3,000 times a minute with water flowing through it failed once, got replaced with the last spare in the building, and then that spare failed too \u2014 which tells you something unsettling about how close TVO came to having no options at all.<\/p>\n
If a nuclear plant this size can quietly lose 17% of its output for years while the grid absorbs it without much notice, it raises real questions about how much hidden capacity the rest of the industry is quietly sitting on.<\/p>\n
The redesigned rotor isn’t due until late 2027, and what happened between September 2024 and now is a story worth reading carefully before you assume nuclear baseload is as reliable as the industry likes to claim.<\/p>\n
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<\/p>\n Energy<\/p>\n New Jersey stood 378 solar panels dead upright in a cattle pasture, edge-on to the sun, because an upright panel gives you two production humps instead of one noon spike, and six cows are now grazing between the rows with a camera on them every five minutes<\/p>\n 10 hours<\/p>\n <\/a><\/p>\n Energy<\/p>\n A 36-mile concrete pipe feeds three desert reactors 72,000 acre-feet of treated city sewage a year, 95 percent of which goes up the cooling towers as vapor, and the contract behind that water runs out in 2050, 17 years before the owner has asked to keep the reactors running<\/p>\n 12 hours<\/p>\n <\/a><\/p>\n Energy<\/p>\n An Illinois reactor that regulators just cleared to run until 2049 was shut off by hand at 4:31 in the morning because an instrument said its control rods were moving when they weren\u2019t, half its protection system fired on its own, and it was still at zero five days later<\/p>\n 13 hours<\/p>\n <\/a><\/p>\n Energy<\/p>\n While the only new reactors finished in the United States in three decades are AP1000s, the Chinese copy of that design got its 1,100-ton steel dome craned on 33 months after the construction license, with everything underneath it still to install<\/p>\n 16 hours<\/p>\n <\/a>AI-generated summary from reviews, comparisons and articles by AutoNotion<\/p>\n Every mechanic has a version of the same speech. Your part\u2019s on order, the car\u2019s fine to drive in the meantime, just don\u2019t sit at 80 on the interstate for an hour until it comes in. So you take it easy, you wait, and a few weeks later the part shows up and you get your car back.<\/p>\n Olkiluoto 2, a boiling water reactor on an island off Finland\u2019s west coast, has been having that conversation for almost two years. Its nameplate is 890 megawatts. It\u2019s been held to 735 since the rotor inside its generator failed, because the utility that owns it would rather give up the power than risk the thing letting go. The replacement it had been waiting on arrived at the plant on July 15.<\/p>\n So the reactor went back up to full power, right?<\/p>\n It didn\u2019t. Teollisuuden Voima<\/a>, or TVO, said the next day that the unit keeps running at the reduced level until a completely new rotor has been installed, and that one isn\u2019t expected at Olkiluoto until late 2027. The refurbished rotor that showed up in July goes on a stand as a spare.<\/p>\n So what does a generator rotor actually do?<\/p>\n Nothing about the electricity leaving a nuclear plant is nuclear, which throws people the first time they hear it. Uranium boils water. The steam hits a turbine, the turbine turns a shaft, and the shaft turns a rotor inside the generator.<\/p>\n That rotor is basically a huge electromagnet, and spinning it inside the stationary windings wrapped around it is what pushes current out to the grid. A coal plant does the same thing. So does a gas plant, so does a hydro dam, and so does the odd tidal machine that bolts its generators onto the blade tips<\/a> instead. Only the heat source changes.<\/p>\n The speed isn\u2019t a styling decision either. TVO lists the rated speed<\/a> of the OL2 turbine train at 3,000 rpm, which is what a two-pole machine has to hold to make 50-hertz power. American machines of the same type spin at 3,600, because our grid runs at 60 hertz. Either way, that rotor holds its speed for months on end without stopping, which is a strange thing to sit and think about.<\/p>\n Here\u2019s where this story actually starts. The generators at Olkiluoto 1 and 2 are water-cooled, so there\u2019s water moving through passages inside a component turning 3,000 times a minute. When that water ends up somewhere it shouldn\u2019t be, moisture readings inside the generator climb, and you don\u2019t get to wait and see what happens next. That\u2019s how TVO caught the fault both times, and it\u2019s why the unit came off the grid within hours on both occasions.<\/p>\n Autonoci\u00f3n Newsletter<\/p>\n No spam. Unsubscribe anytime. Privacy policy (opens in new window)<\/a><\/p>\n That rotor has already been swapped twice<\/p>\n On the morning of Monday, September 9, 2024, moisture climbed inside the OL2 generator and the unit was disconnected from the grid. TVO traced it to the rotor of the water-cooled generator, took the machine apart and installed the last spare rotor left in its inventory. Production resumed on October 6, after 26 days and 20 hours off the grid.<\/p>\n That swap wasn\u2019t a planned job, and it shows in how they did it. TVO put around 35 people in the turbine hall on two shifts, with none of the preparation that goes into an annual outage. The company later cut the whole operation into a one-minute video<\/a>, which I\u2019d recommend if you\u2019ve never watched a rotor come out of a generator.<\/p>\n OL2 came back at 725 megawatts and settled at 735 soon after. TVO kept it there because the cause was still unknown and the rotor now spinning was the last one it had.<\/p>\n Then came April 2025, and this is the sequence I keep going back to. A fresh spare had been delivered, so TVO started walking the unit back up toward full power at 1:00 a.m. on Monday, April 14, expecting to get there by that Saturday. On Tuesday evening the moisture readings climbed again and the unit came down. Communications manager Johanna Aho told Finnish broadcaster Yle<\/a> that the company was investigating \u201cthe matter calmly\u201d and that it was too early to draw conclusions.<\/p>\n It never reached 890.<\/p>\n TVO swapped in the refurbished spare that had landed that same month, and OL2 was back on the grid on the afternoon of May 6, 2025, running at the same reduced level. That rotor is the one turning today. Two failures inside seven months looks like a design problem rather than bad luck, though I can\u2019t find a published root cause from TVO, so we\u2019re all reading the schedule instead of a statement.<\/p>\n So what does the cap actually cost?<\/p>\n The gap is 155 megawatts, and over a year that shows up in the production figures. OL2 generated 6.62 TWh in 2024 and 5.55 TWh in 2025, although the second number also carries the three weeks the unit spent off the grid that spring. At full output, TVO puts OL2 at about 8 percent of everything Finland uses.<\/p>\n