Hugh Pickens writes writes: "The NY Times reports that Japan’s nuclear crisis is on the verge of catastrophe after an explosion at one crippled reactor damaged its crucial steel containment structure and a fire at another reactor spewed large amounts of radioactive material into the air causing most of the 800 workers at the Daiichi facility to leave to avoid exposure to unhealthy levels of radiation at the plant and leaving only 50 workers at the plant to pump seawater into three reactors and fight the fire at the fourth reactor. Prime Minister Naoto Kan briefly addressed the nation on television pleading for calm as engineers struggled to bring the damaged reactors under control but said that radiation had spread from the crippled reactors and there was “a very high risk” of further leakages. The problem at the fourth reactor had not been reported before but according to officials, a fire broke out at that reactor where spent nuclear fuel was being stored. “No. 4 is currently burning, and we assume radiation is being released. We are trying to put out the fire and cool down the reactor,” said chief government spokesman Yukio Edano. “There were no fuel rods in the reactor, but spent fuel rods are inside.” While Japanese officials made no comparisons to past accidents, the release of an unknown quantity of radioactive gases and particles — all signs that the reactor cores were damaged from at least partial melting of fuel — added considerable tension to the effort to cool the reactors. “It’s way past Three Mile Island already,” says Frank von Hippel, a physicist and professor at Princeton. “The biggest risk now is that the core really melts down and you have a steam explosion.”"