Nearly eight months after the onset of the Fukushima Daiichi nuclear disaster, plant operators still aren't exactly sure what the fuck is going on inside its damaged reactors:
Nuclear workers at the crippled Fukushima power plant raced to inject boric acid into the plant’s No. 2 reactor early Wednesday after telltale radioactive elements were detected there, and the plant’s owner admitted for the first time that fuel deep inside three stricken plants was probably continuing to experience bursts of fission.
The unexpected bursts — something akin to flare-ups after a major fire — are extremely unlikely to presage a large-scale nuclear reaction with the resulting large-scale production of heat and radiation. But they threaten to increase the amount of dangerous radioactive elements leaking from the complex and complicate cleanup efforts, raising startling questions about how much remains uncertain at the plant, the site of the world’s worst nuclear disaster since Chernobyl.
Plant operators detected xenon 135, a fission product with a half-life of just nine hours, hence the rush to inject boric acid into the reactor. Boron atoms absorb neutrons, thus interfering with a chain reaction.