According to the Institute for Science and International Security:
ISIS assesses that the situation at the Fukushima Daiichi nuclear plant has worsened considerably. The explosion in the Unit 2 reactor, the third so far, and the fire in the spent fuel pond in the reactor building for Unit 41 means that this accident can no longer be viewed as a level 4 on the International Nuclear and Radiological Events (INES) scale that ranks events from 1 to 7. A level 4 incident involves only local radiological consequences. This event is now closer to a level 6, and it may unfortunately reach a level 7.
A level 6 event means that consequences are broader and countermeasures are needed to deal with the radioactive contamination. A level 7 event would constitute a larger release of radioactive material, and would require further extended countermeasures. The international community should increase assistance to Japan to both contain the emergency at the reactors and to address the wider contamination. We need to find a solution together.
The Three Mile Island accident was a five.
The current situation brings to light another threat. What about all of the other reactors that reside in earthquake-prone regions? Did you know that twenty percent of all the 44 commercial reactors in operation are in areas "of significant seismic activity?" And 62 more plants are under construction and there are 500 more proposals out.
Now some seismologists are wondering if the engineering calculations are good enough to ensure that nuclear reactors have been built to withstand earthquakes. Some experts think that we need to reassess the probability of the big quakes happening. Even though events like this are only supposed to happen every hundred years - there's a possibility that our historical records could be off.
According to Physorg.com, Ross Stein, a seismologist at the US Geological Survey, said:
What happened in Japan "is clearly an indication that we haven't properly thought about events that are well outside our historical experience but nonetheless possible. For me, that is the broad implication for all of us in this field about the weaknesses of our thinking."