JAPAN UNDER GREAT NUCLEAR CRISIS

The situation at Japan's Fukushima Daiichi nuclear plant has been changing rapidly and growing increasingly complex since the earthquake and tsunami hit on March 11. Problems began that day, and each day has brought new, unsettling developments. With unique conditions at each reactor, slightly different responses are required. But the most common response at this point is water. Workers are pumping seawater into the cores of Units 1, 2 and 3 and spray seawater to the spent fuel pools at 3, 4, 5 and 6. Each reactor has a used fuel pool in the upper level of their buildings. Getting water to the spent fuel pools at Units 3 and 4 from the air and ground proved difficult for several days after radiation levels spiked. Safety officials say they continue to be most concerned about the pools at Unit 3 and 4. External power had reached most of the units by March 23. Below is a chart showing the status of each of the six reactors, with the most recent information as possible.

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Reactor No.1	Hydrogen explosion March 12. Primary containment vessel likely not damaged. Seawater is being pumped into the reactor core. Fuel Rods Inside Core: Fuel rods damaged and are fully or partially exposed. The containment vessel is not believed to be damaged. Building: Severely damaged from the March 12 explosion Spent Fuel Pool: No information.
Reactor No.2	Hydrogen explosion March 15, which damaged the containment structure and the pressure suppression chamber. This caused the pressure inside the containment vessel to fluctuate. Seawater is being pumped into the reactor core, and it remains relatively cool, though experts believe radiation has leaked out. Fuel Rods Inside Core: Fuel rods damaged and still partially exposed. Damage suspected to the containment vessel, though the severity remains unknown. Building: Slightly damaged Spent Fuel Pool: No information
Reactor No.3	Hydrogen explosion March 14. Smoke, followed by release of radiation March 16. On March 21 and 23, smoke was seen billowing from the reactor. Fuel Rods Inside Core: Damaged and partially exposed. Building: Severely damaged Spent Fuel Pool: Damage to the fuel rods is suspected and water levels are low. Japanese helicopters attempted to drop seawater on the top of Reactor No. 3 on March 16 and 17 to cool the spent fuel pool. Emergency fire vehicles have sprayed water on the spent fuel pool daily since March 17.
Reactor No.4	Hydrogen explosion March 15, then a fire which heavily damaged the building. The Japanese Self Defense Forces began spraying water on March 20 and continued through March 21. Fuel Rods Inside Core: No fuel rods Building: A blast on March 15 blew an 86 square-foot hole into the wall of an outer building that houses the reactor. The roof is also severely damaged. Spent Fuel Pool: Damage to the fuel rods is suspected and water levels are low. Fire trucks are spraying water on the pool.
Reactor No.5	On March 21, workers switched the reactor to an external power source from the emergency diesel generators. Water is being pumped into the core and the spent fuel pools. Fuel Rods Inside Core: Not damaged; several feet of water covers the tops of the fuel rods Building: Not damaged Spent Fuel Pool: Temperature stable.
Reactor No.6	Unit 6 is running on its own emergency diesel generator. On March 21, the reactor was connected to an external power source. Fuel Rods Inside Core: Not damaged; nearly 6 feet of water cover the tops of the fuel rods. Building: Not damaged Spent Fuel Pool: Temperature stable.