As Japan races against time to control its nuclear crisis, the cooling pools for the spent fuel rods at the Fukushima nuclear plant remain a source of major concern. On Friday water levels in at least one pool – housed in the Unit 3 reactor building – were dangerously low, according to Japanese authorities.
The bad news is that enough fuel rods remain in the pools that, if exposed to air for a long enough period of time, it is theoretically possible that they could burn and melt into a pile of fissile rubble dense enough to restart a nuclear chain reaction.
Tokyo Electric Power said earlier this week that the possibility of such “recriticality” occurring in the pools is not zero. If it happened the pools would then in essence have turned into running mini-reactors, and begin emitting much more heat and dangerous radiation.
Pouring water laced with boron into a pool would help stop such a reaction, as boron absorbs neutrons which are emitted during a nuclear reaction. Japan on Thursday announced plans to import 150 tons of boron from South Korea and France to replenish its stocks.