In the chaos and turmoil following yesterday’s earthquake, the residents of Japan are now grappling with a second horror: a potential meltdown of the the Fukushima nuclear reactors. Several plants have been shut down, and hundreds of thousands have now power after the quakes and tsunami, which may be the strongest ever measured by the Island nation. The Fukushima reactors, about 150 miles north of Tokyo, became a particular focus after the quake shook fuel rods into the core and the loss of power shut off cooling systems. Fears grew after a large explosion there in the early hours of this morning (our time). Authorities confirmed that fuel had melted and have now evacuated over 50 000 people (with some estimates reaching three times that). With the loss of power, cooling systems have been off since yesterday and gasses have been released from the Fukushima 1 plant in order to release the growing pressure inside – preparations to do the same are underway at Fukushima 2 as well. Radiation levels in the are have been rising and authorities are now stockpiling iodine and beginning to check for signs of radiation sickness.

It’s very difficult to tell what’s going on right now. I’ve been glued to newsfeeds for hours now, and every time the situation seems to calm something else pops up. We can all hope that this may not be as bad as Chernobyl or Three Mile Island, but the crisis is far from over. We don’t know how much radiation escaped when they released the pressure, nor do we know what kind of shape the reactor itself is in. As surely as we can expect that the media will overplay disaster fears, we can only expect the government and industry authorities to downplay fears in the public eye. We likely won’t totally understand this for weeks or even years.

The most recent news is stating that at least one more plant, the Fukushima 2 plant (with four reactors of its own, about 10 miles away) is also now at crisis point, and evacuations are expanding.. Attempts to vent gasses seem to have hit some snags, and one of the reactor buildings at Fukushima 1 is now missing its roof, though the reactor itself seems to be intact. Authorities are now attempting to use sea water to cool the reactors, and it seems the temperatures and radiation levels may be dropping.

For those of us who’ve long been highly critical of the nuclear industry, this is a pretty clear example of the kind of “worse case scenario” we’ve been warning about. A nuclear reactor is not an appliance that can be turned on and off. It requires a constant input of attention and energy to keep under control. Without extensive cooling systems and pressure management, a nuclear reactor can produce temperatures which quickly make any attempts to keep the reactor under control nearly impossible. A “meltdown” happens when the fuel rods and the reactor itself simply begin to melt under the stress.

The key to any nuclear technology is the fact that radioactive material gets more radioactive in larger amounts. The neutrons released by the splitting atoms split others, speeding up the pace of the reaction for all the atoms around it. With this principle, you can “breed” special isotopes, or regulate power in a nuclear reactor by inserting or withdrawing rods of feul. It also means, though, that once you have a certain amount of pure enough fuel (“critical mass”), it simply explodes. The difference between a nuclear reactor and a nuclear bomb is that in a reactor, you can control the pace of the reaction. Those lines start to blur when the reactor itself begins to melt.

Are we likely to see an atom-bomb style detonation? Probably not, no. What we’re looking at is a lot more like a cross between a pressure cooker and a dirty bomb. If the reactor cracks open, the high-pressure radioactive gasses will escape into the air. Many parts are in danger of melting or burning – nearly everything does at those temperatures. If the uranium burns, the smoke will carry it for untold distances. It may also simply melt down into the ground until it hits the water table. And any number of new and dangerous isotopes could be created in the process. In short, we don’t need to see a mushroom cloud for this to get really ugly. Chernobyl released a reported 400 times more radiation than the Hiroshima bomb and may have killed over 200 000 people.

Thousands of demonstrators have already turned out in Germany to protest a local nuclear plant after hearing of this crisis, and many other questions are now being raised about how “safe” nuclear power can ever be.