The reactor situation in Japan suffered yet another setback today, with water levels in Unit 2 registering 10 million times normal levels. The radiation was so high that workers fled the reactor rather than take a second reading. Radiation levels were an astonishing 1,000 msv/hour (which will cause radiation sickness within an hour and even deaths starting at 6 hours). Given this near-lethal radiation field, workers evacuated Unit 2.
One question is: where did this radiation come from? Most of it was in the form of iodine-134 (with a half-life of 53 minutes) and iodine-131 (with a half life of 8 days). This indicates that the radiation came directly from the core at Unit 2, rather than the spent fuel pond (where most of the iodine has already decayed). So there seems to be a direct path way from the core to the outside, meaning a breach of containment, similar to the situation in Unit 3. In other words, there could be a crack in the pressure vessel surrounding the super hot uranium core, as well as a crack in the outer primary containment vessel surrounding the pressure vessel. These cracks may allow radiation to escape from the core directly into the environment.
At the very least, this means continued leaks of deadly radiation from the core to the outside world.
But in a worst case scenario, it could be a preview of the day when radiation levels are so high that a complete evacuation is necessary. This means that the cores, without cooling water, will heat up and eventually cause an explosion, (via a hydrogen gas or steam explosion). Remember the only thing preventing this worst case scenario are brave firemen shooting hose water into the cores and spent fuel ponds. Once they are evacuated, then simultaneous meltdowns at 3 nuclear sites is inevitable. Then a steam or hydrogen gas explosion may crack open the pressure vessel, leading to a catastrophic release of radiation, perhaps worse than Chernobyl.
So it is a race against time. On one hand, we have the brave workers trying desperately to keep thecore and spent fuel pond covered with water. On the other hand, the reactors are deteriorating every day, with the possibility of cracks, pipe breaks, secondary earthquakes, which could easily tip the accident into the worst case scenario. At that point, when all the workers have to evacuate, let's hope that the utility took my advice to prepare the Chernobyl option (i.e use the air force for bury the reactors in concrete and sand). However, I doubt that the utility has thought that far ahead.