Based on new estimates of the radiation that has been released, Fukushima now has the worst score on the IAEA's accident rating scale. But much about the reactors, and their future, is still unknown.
Workers plugged a leak of highly radioactive water into the ocean from Japan's Fukushima Daiichi nuclear power plant Wednesday, even as they tried to prevent another hydrogen explosion in reactor No. 1 by injecting nitrogen gas.
Japanese officials allowed owners of the damaged Fukushima nuclear power plant to empty tanks holding 10,000 tons of slightly radioactive water into the ocean – in order to make room to pump highly contaminated water out of reactor No. 2.
The contaminated pools in the reactor turbine buildings have created a tough new challenge for officials trying to contain the Japan nuclear crisis. The source of radioactivity is a mystery.
Levels of radioactive iodine reached 1,250 times above normal in seawater off the coast of Japan's stricken Fukushima Daiichi nuclear plant, raising concerns about a containment crack.
Japanese authorities began testing for radiation in seawater near the damaged Fukushima Daiichi nuclear plant on Tuesday, but officials stressed that the elevated levels are no cause for worry.
The power to operate cooling pumps, a challenge at the heart of the Japan nuclear crisis, is on the verge of being restored, and a detailed assessment by a US expert is notably upbeat.
But workers made progress over the weekend on restoring electricity to the cooling system at Japan's Fukushima nuclear power plant, which will help stabilize overheated reactors.
Japan pours tons of water into a reactor building where the water level in a cooling pool for spent fuel rods was dangerously low. The nuclear crisis is now rated as severe as Three Mile Island.
Reports suggest that greed within the worldwide nuclear industry, combined with an insufficient UN watchdog and lax oversight of Japan's nuclear plants, contributed to the Japan nuclear crisis.