One other thing I would like to point out is that with the possibility of a China Syndrome that would occur shortly after shutdown the problem would be from the fuel becoming in close proximity to itself. By this I mean that either the fuel rods degrade due to Zirc Hydration allowing the fuel pellets to come close together or the fuel actually melts. Since the uranium is very heavy it would tend to go to the bottom of the pile. As it get into close proximity it then goes critical causing more heat which could then burn through the containment structure. Then as this pool of fuel burns it way down it would hit the water table which would cause a steam explosion blowing the whole mess apart and spreading serious contamination with high level radioactive daughter products of fission. Along with that it could contaminate the water supply for a large area.
That was a huge concern at Chernobyl. Several people willingly went in and dug up the area under Chernobyl and installed a cone shaped column that distributed the mess so that it could not reach the water table. These men were unsung heroes who willingly gave up their lives to save the Ukraine. Also, there we others who gave up their lives to fly helicopters dropping water on Chernobyl. Chernobyl was a much worse case scenario than Fukishima even though Fukishima affect several plants.
One of the most fascinating bits of info I ever ran across are the natural fission reactors that existed here on Earth at Gabon (Africa) long before man came along. Pretty neat, that they operated all by themselves for several 100 thousands of years and no meltdowns. They even "turned themselves on and off" when water stopped flowing.
I have never heard about the natural reactors. So I guess I have a lot to learn about them.
One other major radiation disaster happened in Idaho, I think it was in 61. The Army was trying to develop a small nuclear reactor and had a system set up on the National Reactor Testing Facility West of Idaho Falls. It was designated SL-1. The reactor was shut down and they were doing maintenance. The had the control rods inserted but the mechanisms were taken apart. One of the technicians was fooling around with another technician's wife and he was upset. Upset enough that he supposedly pulled one of the rods out by hand, actually yanked it out. Several things affect the criticality of a reactor. The temperature of the water is one of them. As the water gets colder it is denser and acts better as a reflector and a moderator. So this reactor was closer to criticality because of that. Also, nuclear reactions happen at 10 to the minus 23 seconds. So each generation is infinitestably short. So if you insert a lot of reactivity, even if it is not enough to go critical under stable conditions, it can cause a major uptick in reactivity. Since this happens so fast it didn't have time to naturally turn around the reactivity and it overshot drastically. This high level of power overshot and almost instantly boiled the water out of the reactor causing it to create steam. The steam blew apart the reactor and caused a radioactivity release. The operator who pulled the control rod ended up stuck to the ceiling of the reactor room. Several other operators and technicians who were there died also from radiation poisoning. Radiation alarms across the site went off and when they investigated they found this plant was the cause.
What triggered that memory was the reference to the natural reactors and the water. I just read the report on the natural reactors and it is interesting.
Report from New Scientist, just a few days ago, ends with this:
On an international level, even if all the waste from Fukushima was dumped neat into the Pacific, dilution would eliminate any radiation risks to distant countries like the US, says Simon Boxall of the National Oceanography Centre in Southampton, UK.
The ocean would be the safest place for the waste water, says Geraldine Thomas, who runs the Chernobyl Tissue Bank at Imperial College London. "But to make that politically acceptable they have to talk to the local population. They have to make people understand that low levels of radiation don't matter because we're all exposed to it all the time."
In other words, it is more of a communication problem than a public health problem. "None of this is going to do anything health wise," she says. "Fukushima is nothing compared to Chernobyl."
Originally posted by rinselberg: article: "In other words, it is more of a communication problem than a public health problem. "None of this is going to do anything health wise," she says."
It seems the choice we have, is to take their word for it.
I would go there again. It's a beautiful place, but very expensive. You can rent waterproof cameras for underwater stuff. (You can rent anything really)
Originally posted by Raydar: I tend to believe that sooner or later, an uncontrolled melt is inevitable. At some point, the area around the site is going to become too contaminated to be worked in or around.
I suppose my question is what would happen in such a situation? I would think that there would be a nice beam of radioactivity projected out of the hole in an ever narrowing beam. Probably accompanied by lots of radioactive steam. (Or at least particulates, since radioactive water is not a possibility. Did I get that right?) At some point, I have to believe that the earth would just fall in on the molten blob. Would that tend to cause it to go critical and explode? Or would it, at some point, just reach a depth where it would become insignificant? As hot as the earth is, below ground, it makes me wonder if it would reach a certain level and just disburse in the rest of the molten material.
Could make an interesting sci-fi film, for sure. ("China Syndrome II, the aftermath", anybody?) Not to make light of an ugly situation.
