DISCLAIMER: I don't like having to put a disclaimer on this post, but some reactions to this diary make me think it's a good idea. I am not a nuclear engineer. I do not claim to be an authority on these matters. This diary is simply trying to synthesize some information I have found in researching this myself. Some of the information is also outdated, and more may become outdated. So please take this with a grain of salt.
I've been doing a whole lot of reading about the Fukushima plant over the past few days, and have also been reading about nuclear power plant design in general. And while there are certainly a lot of hazardous things happening, it's not the end of the world. And in my opinion, it also shouldn't be the end of our use of nuclear power. Here's why.
EDIT: I had a link posted here that I have been informed is from a very shady source, so I've removed it. Might be some serious intellectual dishonesty going on here, so sorry about that.
When I was growing up in the 80s, I found the idea of nuclear war to be extremely frightening. I watched a movie once, called Testament, about the horrible experiences that a family endured after a full-scale nuclear war happened, quite by accident. It's one of the only times that I can recall where I had so much trouble sleeping that I had to ask my parents if I could sleep with them. The depictions of radiation sickness were particularly disturbing for me. For many years, I harbored a fairly irrational fear of radiation in general. For me, any radiation exposure was too much.
But at the same time, as I got older, I became fascinated with chemistry and, in particular, the elements beyond uranium on the periodic table. Perhaps this is not unusual. An irrational fear turned into curiosity is something that is pretty common in my experience.
In fact, I ended up majoring in physics in college, and am now working on my Ph.D. in high energy physics, working on one of the experiments at the Large Hadron Collider at CERN in Switzerland. It's pretty fascinating stuff.
In the course of my undergraduate research, I had to take a radiation safety class so that I could work in the high energy physics lab at my university. And given my fear of radiation as a kid, I thought it would be interesting. And it most certainly was. Whereas when I was a kid, I thought that any radiation exposure was bad, it turns out that we are all constantly exposed to radiation from various sources. There are cosmic rays showering down on us all the time from high energy particle interactions in the outer atmosphere. Most rocks, some more than others, have fairly high levels of radioactivity. Granite, in particular, has a high level of alpha-emitting radiation. But most of this isn't harmful. Alpha particles (helium nuclei that escape from very heavy nuclei) can't even penetrate the outer layer of skin on your body.
Now, obviously not all radioactivity is good. Exposure to radiation is harmful depending on the amount of radiation that a person is exposed to and the amount of time that the exposure lasts. The amount of radiation allowed for most people to be exposed to in a given year is quite small; radiation workers are allowed more. And while radiation has been shown to cause many forms of cancer, there are also some very interesting studies showing that the human body can be very resilient even against large exposures to radiation. For example, while many people who were young at the time of the Hiroshima and Nagasaki bombings have contracted thyroid cancer (which can be mitigated by taking stable iodine at the time of exposure), even many years later, developing cancer was not a foregone conclusion. More info here. The long-term health effects of radiation exposure not resulting in immediate radiation sickness are not entirely clear.
Radiation is clearly detrimental to health in many cases, but it is not an immediate death sentence in lower doses, nor is it necessarily a long-term problem in every case either. The human body heals itself quite well most of the time.
Nuclear power, when practiced using technology similar to most older nuclear reactors in the US and other countries, produces a fairly large volume of waste. Most of this waste is short-lived radionuclides like Cesium-137. This stuff is highly radioactive, but the other side of the coin is that the "hotter" a radioactive source is, the shorter the time is that it will stick around. If you have a large quantity of Cesium-137, for example, 99% of that will have decayed away within a matter of decades, and the activity decreases exponentially. There are much longer lived radionuclides that end up in the nuclear waste though. These are called actinide waste and consist of transuranic elements -- elements heavier than uranium. Some of these have half-lives of hundreds of thousands of years.
So far, we've had some small doses of fission products, like Cs-137, released into the environment from the Daiichi plant. But while some of the core material in some of the Fukushima reactors has likely melted (mostly the zirconium cladding around the UO2 fuel pellets, which are ceramic and can withstand very high temperatures) it is all contained within the concrete and steel containment vessels. Radiation levels at the plant are still fairly low. The cores of all of the reactors remain contained. By the way, this is what is designed to happen in a loss of reactor cooling, and this containment is precisely what was missing from the Chernobyl reactor accident.
There is no runaway criticality in any of the reactors. The core materials are very likely to remain contained.
The biggest problem so far has come from the spent fuel stored outside the reactors. This spent fuel needs to be covered in water. If the water level drops too low, the rods can heat up and the zirconium cladding can catch fire. This can obviously spread radioactive materials over a large area. But part of the problem -- that the spent fuel rods are now exposed to the environment -- is actually quite helpful in this case. The rods need to be submerged in water, and an open building allows crews to put that water where it is needed. We're clearly not out of the woods yet on this problem, but it's clear what needs to be done: keep the spent fuel rods covered in water.
Now I need to say something about the Fukushima plant in particular. The first reactor, number 1, was actually commissioned in 1969. It achieved criticality the next year. This means that the reactor is over 40 years old. The reactors at this plant are all of the same GE/Hitachi design. As it turns out, these plants are of a pretty old design, and it's one that's not in use in any new plants. The cooling system is active. This means that water needs to be actively pumped into the reactors in order to keep them cool. But there are a lot of newer designes that don't require this at all. One design in particular, the Advanced Boiling Water Reactor, uses gravity and convection effects to cool the reactor. In this sort of reactor there is no fuel melting when coolant isn't actively circulated, because there is no active circulaton. There are many other third-generation reactor designs that achieve similar results. You can read more about them here.
There are even some new reactor designs that can significantly reduce the amount of transuranic waste that is generated by a reactor. So-called fast neutron reactors actually burn up the actinide waste, so that the residual matter from spent fuel is almost all short-lived waste like Cs-137. So instead of having to find a place where you can store nuclear waste for thousands of years, you only need to store it for decades before it is much less active and can be much more safely disposed of.
The point is that while there are some clear design problems with the GE/Hitachi reactors at plants like Fukushima, almost all of these design problems have been solved in newer reactor designs. Active cooling can be lost when you have a loss of power to the nuclear power plant. Backup systems can fail. But newer reactor designs don't require active cooling at all. They are self-stabilizing.
But even with these design flaws, the reactor material is remaining contained, and is very likely to remain so. As long as engineers can keep the spent fuel cool until power and normal cooling can be restored, this accident is unlikely to produce any substantial release of dangerous radioactivity into the environment.
Radioactivity is frightening stuff. You can't smell it, or taste it. You can't really see it either. But that's no reason to panic about it either. A little knowledge can really help provide some perspective. And the truth is that while a nuclear catastrophe resulting from the release of large quantities of highly radioactive material would be severely detrimental to the environment, that has only happened once (at Chernobyl) in a reactor that had almost none of the safety features that the ones at Fukushima have. And newer reactors have even more safety features.
Let's try to have some perspective about that when we talk about the future of nuclear power. Demonizing it isn't the answer.