Extremely precarious situation. It's a race against time to create the technology to decommission all six nuclear plants at the site before disaster (earthquakes, tsunamis, equipment breakdowns) causes the stricken plants to reach criticality.
Japan's recent (Dec. 2013) State's Secret Act created a pall over the free flow of information to remediate the disaster. Repercussion of another disaster could have global consequences to humans.
Three melted cores produce high levels of radiation, which is picked up by both the water used to cool the cores and the ground water that seeps into the plant. TEPCO began releasing tainted water into the Pacific.
Several spent fuel pools with hundreds of tons of radioactive fuel are 5 stories off the ground and are susceptible to seismic activity.