Radiation is now coming out of the breach. We are in unknown territory but with the Japanese evacuating the workers at No. 2, it is likely that the fuel rods will fully melt down.

James Pilant

New York Times

Japan faced the likelihood of a catastrophic nuclear accident Tuesday morning, as an explosion at the most crippled of three reactors at the Fukushima Daiichi Nuclear Power Station damaged its crucial steel containment structure, emergency workers were withdrawn from the plant, and a fire at a fourth reactor spewed large amounts of radioactive material into the air, according to official statements and industry executives informed about the developments.

“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,” the chief government spokesman, Yukio Edano, told a televised press conference. “There were no fuel rods in the reactor, but spent fuel rods are inside.”

Government officials also said the containment structure of the No. 2 reactor had suffered damage during an explosion shortly after 6 a.m. on Tuesday.

They initially suggested that the damage was limited and that emergency operations aimed at cooling the nuclear fuel at three stricken reactors with seawater would continue. But industry executives said that in fact the situation had spiraled out of control and that all plant workers needed to leave the plant to avoid excessive exposure to radioactive leaks.

CNN

Japanese authorities trying to stave off meltdowns at an earthquake-damaged nuclear power plant reported more grim news Tuesday as radiation levels soared following another explosion at an overheating reactor.

The risk of further releases of radioactive material from the Fukushima Daiichi nuclear power plant remains “very high,” Japanese Prime Minister Naoto Kan said Tuesday. In addition to an explosion at the No. 2 reactor, the building housing the No. 4 unit — which had been shut down before Friday’s earthquake — was burning Tuesday morning, Chief Cabinet Secretary Yukio Edano announced.

The plant’s owners, the Tokyo Electric Power Company, evacuated all but about 50 of their workers from the plant following Tuesday’s explosion at the No. 2 reactor. Radiation levels at the plant have increased to “levels that can impact human health,” Edano said — between 100 and 400 millisieverts, or as much as 160 times higher than the average dose of radiation a typical person receives from natural sources in a year.