poto wrote:I'm not worried about Japan's reactors. They are well designed and their people seem to have the situation under control. I don't think there is any real risk of losing containment at this point. If I am wrong and a worst-case comes true, the containment vessel that the reactor core is located in is designed to contain a complete core meltdown. This means there is no chance of a Chernobyl happening.
The venting of steam does not pose any significant large-scale radiation risks. It's good that they are able to vent the excess pressure and pump more water to the cores. Just being able to pump water means they are not going to lose containment and a full meltdown is no longer a risk. Really, I think a lot of people are allowing themselves to be subjected to media-induced panic over this.
A Japanese friend of mine said the same thing today. Would those of you (such as poto and mawkish) who understand the mechanics of this- how the containment vessel can contain a complete core meltdown- explain it for us, in layperson's terms? Also, why are these hydrogen explosions "safe" - why is there no concern
among some scientists that the vessels could crack or break or rupture, while there is great concern among others?
OK, I'll give it a shot. This may not be 100% accurate as I am not a nuclear expert, but this is my take on a worst-case.
The reactor itself at Fukushima is a GE BWR Mark III reactor I believe. In the case of a complete meltdown, they will open the valves designed to vent steam and allow all the water to safely boil off. Then the fuel rods themselves will melt and turn into a shallow pool in the bottom of the containment vessel. Spreading it out will help it cool. Then coolant will be pumped in to further cool it. This will prevent the core from ever exploding and no significant radiation will be released. After a while, the remnants of the core will be collected and shipped to a reprocessing facility. Of course, this worst-case is not going to happen as long as they are able to keep pumping water into the reactors which they have been able to do.
Anybody familiar with the design and engineering of those reactors isn't worried about loss of containment. They are designed to safely contain a complete core meltdown. Chernobyl had a badly flawed designed and incompetent operators. It is not fair to compare the 2 as some in the media have attempted to do. I suspect that many of the people who are spreading fear and panic are anti-nuclear people trying to push an agenda at the expense of others.
The hydrogen released does not contain any uranium or any other nasty particles in significant quantities. Basically, the fission products are being contained in the containment vessel as it was designed to do. I have heard that a small amount of cesium and iodine were released. These are not good, but the amounts were pretty small and diluted in the atmosphere quickly. If anyone was nearby at the time of the venting and got exposed, they probably got about the same exposure as what an airline pilot gets in less than 6 months of flying. Not a big deal and certainly not lethal unless possibly you were standing directly on top of the vent at the time of the venting.
The iodine is really the only thing I'd be worried about, but even it only has a half-life of 8 or 9 days IIRC, so it will be gone fairly quickly. The issuing of iodine tablets is a standard precautionary procedure. People who live down-wind of nuclear plants here in the states are sometimes sent free iodine tablets as a precautionary measure.
To my knowledge not a single person has as yet died of radiation poisoning, and I do not think that any radiation deaths will be forthcoming. Meanwhile, many thousands have died from the earthquake and tsunami. My heart goes out to those who have lost friends and loved ones in this disaster.