The Czech utility \u010cEZ spent Friday morning sharing some pretty good news with reporters. Its Temel\u00edn nuclear plant is switching to fuel from Westinghouse, the American reactor company, after eight years of analysis and testing, and its other nuclear plant, Dukovany, is lined up to follow once its own testing and licensing are done.<\/p>\n
By that evening, one of Dukovany’s four reactors was on its way offline.<\/p>\n
At 8 p.m. local time on October 30, operators started bringing the power down on unit 3. Its first turbine came off the grid at 12:42 a.m. on Saturday, October 31, and the second one followed at 2:06 a.m. That’s 7:42 and 9:06 p.m. Friday on the East Coast, if you were up watching the grid in Central Europe for some reason.<\/p>\n
The cause is a small leak in one valve, which staff caught during a routine check, according to plant spokesperson Radek Dole\u017eal. He told the Czech news agency \u010cTK, in a report carried by oEnergetice<\/a>, that the leak has no effect on nuclear safety, and the plant’s other three reactors kept running at 100%.<\/p>\n So why switch off a whole reactor over one small leak?<\/p>\n The State Office for Nuclear Safety<\/a>, or S\u00daJB, is basically the Czech version of the NRC. It said the unit would be disconnected from the grid and cooled down so the repair could be carried out, which tells you this isn’t a job anyone wanted to try with the reactor running.<\/p>\n Dukovany’s reactors are pressurized water reactors, a Soviet-designed model called the VVER-440. In a reactor like that, the water carrying heat away from the core is kept under enough pressure that it stays liquid well past the temperature where it’d normally boil. You don’t want anybody loosening fittings on plumbing in that state, so the plant brings the temperature and pressure down first.<\/p>\n Now, I can’t tell you exactly why this particular valve needs a cold reactor. The word \u010cEZ used is “armatura,” which in Czech power-plant speak covers valves and the hardware bolted around them. The company hasn’t said which valve it is, which loop it sits on, or how much leaked, and S\u00daJB’s notice doesn’t get into it either.<\/p>\n Frankly, this is about as boring as a leak story at a nuclear plant gets, and boring is what you want here. Somebody found a small problem during a routine check, and the plant took the unit offline to fix it rather than nursing it along until the next scheduled outage.<\/p>\n It’s also a slower, calmer kind of shutdown than the one we covered at an Illinois reactor that was shut off by hand at 4:31 in the morning<\/a> in September. That one, Dresden 2, went from full power to zero in one move. Dukovany 3 took more than six hours to wind down, on a schedule the regulator had posted earlier that day.<\/p>\n There’s one quirk in the paperwork, though. S\u00daJB’s notice calls this a planned shutdown, while \u010cEZ and the Czech press call it unplanned. Both are kind of right. The power-down was planned in the sense that it was scheduled for 8 p.m. that Friday. It just wasn’t planned months ahead, the way refueling outages are.<\/p>\n A VVER-440 doesn’t feed one giant turbine. It feeds two, each with its own generator, and \u010cEZ lists each Dukovany unit at 512 megawatts<\/a> across its pair. When a unit comes down, operators ease the reactor’s power off over several hours and take the turbines off the grid one at a time. Unit 3’s two came off 84 minutes apart.<\/p>\nSome fixes can’t be done hot<\/h2>\n
Why there are two timestamps<\/h2>\n