On 03/21/2011 08:31 PM, Jed Rothwell wrote: > ... > I still think something is fishy about the fact that the pond went dry > even with 700 people there. Someone should have kept an eye on the one > in #4. They could have brought a hose up there before the water level > fell enough to expose the rods and make the room to dangerous to enter. ...
Indeed. Sez the WSJ, "The Fukushima Daiichi power plant was already one of the most trouble-prone nuclear facilities in Japan, even before the devastating earthquake and tsunami that knocked out its cooling systems and precipitated the worst nuclear crisis in 25 years, a Wall Street Journal analysis of regulatory documents shows." http://online.wsj.com/article/SB10001424052748704433904576212980463881792.html?mod=djemalertNEWS (link may be subscriber only -- not sure. What follows is just a few more excerpts from the article.) They then go on to add something we already had heard about (from Horace, I think), "In addition, a standard practice at Japanese nuclear plants—to remove fresh fuel from a reactor and park it for weeks or months in a less-protected "spent fuel" pool during maintenance—appears to have been a significant contributor to the crisis, engineers say." The article says lots of stuff we've heard before, and then adds, "The events at Reactor 4 expose the risk of a commonplace practice in Japan, "full core discharge," in which all the fuel in a reactor is moved during maintenance shutdowns. "The Japanese argue it's safer to move all the fuel to the pool, but the practice of full-core discharge caused a problem, in this case," said Andy Kadak, a former professor of nuclear engineering at Massachusetts Institute of Technology, who has studied fuel handling for Tepco. Mr. Kadak said the Japanese feel the pools are safer because all the fuel is kept in a neutralized space removed from workers." And, "In the U.S., reactors shut down for refueling typically retain most of their fuel in the thick steel reactor pressure vessel that provides much more protection against a radioactive release. During refueling outages, when operators swap out depleted fuel for fresh fuel and do other maintenance, these rods are shuffled around in a process somewhat akin to rotating tires on a car to even out the wear. "In the U.S., only the most worn-out rods typically are removed and transferred to a spent-fuel pool for storage, where they can stay for decades. Thus, U.S., pools hold only the oldest spent fuel, which is also the coolest in terms of temperature and radiation." Eventually the article gets back to the long term problems with the plant, "The Daiichi plant has had 15 accidents since 2005, the most of any Japanese plant with more than three reactors, according to an analysis of the data by the Journal. Maintenance problems have been a leading cause of accidents at the plants, but it isn't clear whether age has been a major factor." And, a little later, "The Daiichi plant does expose its workers to more radiation than other plants, the regulatory documents show. Daiichi employees have received the highest average radiation doses of those at any Japanese plant every year over the past decade. Tepco's other plants also exposed their workers to higher doses of radiation than most other big Japanese operators." Charming.
