The operator of the Fukushima Daiichi nuclear power plant stood ready Thursday to inject boric acid into one of its most heavily damaged reactors after it found steam emanating from the reactor building. The preventive measure would stave off sustained nuclear reactions in the reactor’s damaged core. http://www.nytimes.com/2013/07/19/world/asia/steam-detected-at-damaged-fukushima-reactor.html?hp&_r=0  Remote camera footage Thursday showed steam escaping from the top of the No. 3 reactor’s primary containment structure, which houses its fuel vessel. Any further trouble, such as a rapid rise in temperature or radiation parameters would raise the chilling possibility of criticality in the reactor’s damaged fuel, most which is thought to have melted and slumped to the bottom of its containment structure after the hydrogen explosion, one of several at the site in 2011. Boric acid would slow that rate of fission, preventing the worst-case scenario of uncontrolled nuclear chain reactions in the core.
Fresh trouble at the No. 3 reactor is especially worrying because it contains mixed uranium-plutonium oxide fuel. The upper floors of the reactor also house its fuel pool, which stores over 500 fuel assemblies. The reactor complex’s basement is flooded with highly radioactive water. Studies show that an accident like a meltdown or containment failure in a reactor that holds such fuel would result in more cancer deaths than one in a reactor fueled only with uranium.
More than 100,000 people fled their homes after the meltdowns at Fukushima, the world’s worst nuclear crisis since the Chernobyl disaster in 1986.