Here's the reason why the Fukushima crisis was just elevated to a level 6 out of 7

Workers are being evacuated again and authorities are encouraging people living within the 20-30 km safe zone to either "stay indoors" or "leave"

Recent elevated levels of radiation are raising speculation that the floor of the problematic and highly dangerous reactor 3 has been compromised.  This unit has the most potential for danger because it uses mox, a highly volatile mix of uranium and plutonium.  Two plant workers were hospitalized yesterday from coming in contact with water from this reactor. NHK reported that water in basement 3 has 10000 x the radioactivity as the water inside a normal operating reactor, hence the assumption that unit 3 containment may be breached, and leaking water either from the core or the spent fuel pool.

Meanwhile, there are estimates that 57,000 pounds of salt have accumulated in Reactor No. 1 and 99,000 pounds in Reactors No. 2 and 3. This build-up may potentially cause the reactors to overheat and possibly even meltdown, though the exact levels of dangers incurred by salt are unknown. The U.S. is sending two barges containing 2 tons of fresh water to help stave off further corrosion to equipment, and hopefully, the water will actually find its way into the reactors.

Levels of Iodine 131 in Tokyo tap water have reportedly dropped to safe levels.  Readings now at 70 Becquerels/liter indicate that recent precipitation in Tokyo was the primary contributor to the elevated amounts observed a few days ago.  In the near term, levels of iodine131 in Tokyo's tap water will rise and fall depending on wind direction and radioactive venting.