Fairewinds' Chief Engineer Arnie Gundersen discusses whether the accidents at Fukushima were a meltdown, a melt-through, or a China Syndrome. Whatever the accidents are named, thousands of tons of water contaminated with plutonium, uranium, and other very toxic radioactive isotopes are flooding the site, the surrounding water table, and the ocean.
Arnie Gundersen: Hi, I'm Arnie Gundersen from Fairewinds.
Last week, Tokyo Electric announced that the core inside the nuclear reactor had definitely melted through and had also melted partly through the containment at Fukushima. I wanted to talk about that today because I think that there have been a lot of exaggerations and misunderstandings on the internet about what is actually going on.
So the question I would like to talk about today is, can Fukushima become what is called The China Syndrome? And what exactly does The China Syndrome really mean?
(Clip of The China Syndrome begins)
(male actor #1) "I don't know. They might have come close to exposing the core.
(male actor #2) "If that is true, then we came very close to The China Syndrome."
(Jane Fonda's Character) "The what?"
(male actor #2) "If the core is exposed, for whatever reason, the fuel heats beyond core heat tolerance in a matter of minutes. Nothing can stop it and it melts right down through the bottom of the plant, theoretically to China. But of course, as soon as it hits ground water, it blasts into the atmosphere and sends out clouds of radioactivity. The number of people killed would depend on which way the wind is blowing, render an area the size of Pennsylvania permanently uninhabitable, not to mention the cancer that would show up later."
Arnie Gundersen: The term is really old; it dates back at least until the 60's. And what it means is that the nuclear core melts, and of course it is an American term, so it melted from America toward China through the center of the earth. That is what the term means. It is an over-exaggeration to begin with, but it does mean that the nuclear core leaves the nuclear reactor, leaves the containment, and gets into the earth. That is what a China Syndrome really means. Now I will be using some rather crude demonstration items today. I realize a lot of engineers watch this and just bear with me here. I think these are analogies and they are always a little risky, but I do think they explain what is happening inside Fukushima.
The first phase of the accident was when the nuclear reactor core lost it's cooling. Now you will remember uranium atoms split; 95% of the power comes from uranium atoms splitting. But these pieces that are left over are called fission products, and they retain a lot of heat. When you shut a nuclear reactor down, a process that takes about 2 seconds, 95% of the heat stops immediately, but 5% of the heat cannot be stopped. That, as long as there is extra water flowing, is all you need to keep a nuclear reactor cool. You remember back in April, I did a video where I talked about a nuclear reactor fuel pellet. It was about as big as my pinkie, and the fuel rod is about the diameter of my pinkie, but 12 feet long. In a lot of ways, it is like spaghetti. It is just as flexible as spaghetti, but of course it is 12 feet long. And there are thousands of these nuclear fuel rods inside a nuclear reactor. A nuclear reactor is not anything but a glorified pressure cooker. A pressure cooker cooks at 15 pounds. A nuclear reactor cooks at 1,000 pounds. But essentially they are the same thing: they are designed to hold really hot water and not to leak.
Well, the nuclear fuel is placed into the nuclear reactor, and as long as the water is in there, everything is fine. But like when you overcook spaghetti, what happens? It can form a blob on the bottom of your pressure cooker. That is what happened at Fukushima. The decay products created enough heat to boil off all the water, the nuclear fuel collapsed, the pasta broke, and is now a blob at the bottom of the nuclear reactor. That happened in about 6-8 hours on Fukushima I and perhaps as long as 10 hours on Fukushima II & III.
So the first phase of this accident is called a meltdown. That is when the pasta collapses and lays in the bottom of the pressure cooker. That is when the nuclear fuel melts and lays in the bottom of the nuclear reactor. Phase one is a meltdown.
The second step in the process is something called a melt-through. Now we are at a point where we have got a blob of nuclear fuel at the bottom of the nuclear reactor vessel. TEPCO is saying that the nuclear reactor vessel is about 8 inches thick, about 30 centimeters thick, and that is enough to hold the nuclear fuel for quite a long time. I do not think that part of TEPCO's analysis is right. I have talked about it before, but on a boiling water reactor, there are over 60 holes in the bottom of the reactor for the control rods to go in and out. And the Nuclear Regulatory Commission has already identified that it is likely that the nuclear fuel did not have to melt through the 8 inches of steel, but instead could do an end run around that and shoot out holes at the bottom of the reactor.
So almost like soft ice cream falling out of a dispenser, it is like hot nuclear fuel pouring out of these holes on the bottom of the reactor. That phase is called a melt-through. Probably within a day of the beginning of the Fukushima accident, we were in the phase where nuclear fuel was melting through the nuclear pressure vessel.
Now remember the nuclear reaction has stopped. None of this is heat from the chain reaction and all of it is coming from the nuclear daughter products. After about a day, instead of about 5% of the heat coming from the nuclear daughter products, we are down to less than 1% of the nuclear heat. So now we have got a blob that has left the pressure cooker, and is now lying flat on the floor underneath the nuclear reactor.
There are some assumptions here. If there were a crater on the bottom of the nuclear reactor, the blob would have fallen into that crater and the heat would have been concentrated. That would have allowed this nuclear blob to work it's way down into the nuclear containment faster. And again, that is an assumption. No one really knows what is really going on underneath that nuclear reactor. No one can get within 100 feet of the bottom of that nuclear reactor. And it will be 20 or 30 years before we really find out what that area looks like. But the assumption is that the nuclear fuel lying on the floor, has begun to eat away at the containment. So phase 2 is when it ate through the containment.
Phase 3 is the beginning of what would ultimately become a China Syndrome. At the bottom of the nuclear containment is about 3 feet of concrete and about 2 inches of steel. We are quite certain that the nuclear fuel has left the reactor and is lying on the bottom of the containment. The question is how deep into the concrete it has worked it's way and has it broken through the steel? I do not think it has broken through the steel and I think it is perhaps as much as a foot or two into the 3 feet of concrete. But that does not make a China Syndrome. The reason it is not working it's way down any further, is because the radioactive daughter products are no longer generating anywhere near as much heat as they did on the very first day of the accident. In fact, they are probably generating less than a million watts of power right now. Now that is a lot of heat: a million watts is ten thousand 100 watt light bulbs and you can imagine that that would generate a lot of heat. But compared to what was available on the first day, and the second day, and first week, the amount of decay heat is very small.
In addition, right above all this nuclear melted fuel, is an awful lot of water. The water is at less than 100 degrees Centigrade. It is not boiling. And what that means is that there is an enormous ability for that water to suck the heat out of the nuclear core as it lies on the bottom of the containment. I do not believe that the nuclear core can melt down through the containment and into the water table. There have been all sorts of postulations about violent explosions from this. And again, I do not think that can happen because the amount of heat available (now we are almost 9 months after the accident) is not great enough to create what is called a steam explosion.
So the good news is I do not think a China Syndrome can happen. I do not think this core can keep melting into the bottom of the earth. And I do not think there will be a steam explosion either. That is the good news.
Here is the bad news. That nuclear core is in direct contact with tons of water. And that containment, while not leaking down, is leaking out the sides. That contaminated water is going into every other building on site. And there is literally thousands and thousands of tons of water in other buildings. That water contains radioactive cesium, radioactive strontium, and it also contains nuclear fuel. There will be uranium in that water and plutonium in that water as well. We know for sure that that water is leaking into the ground water and into the Pacific Ocean. So while it is important to know that we are not going to release the nuclear core directly into the center of the earth, the problem is not over. And as a matter of fact, the problem will last for tens, perhaps even as long as 30 years because this contaminated water is in the basements of all the buildings on site. And not only does it contain cesium (that hangs around for 300 years), strontium (hangs around for 300 years), but it also contains plutonium and uranium and they have half lives of tens of thousands of years.
So the problem is, what do we do with all that water that is contaminated? It is already leaking into the groundwater. It is already leaking into the ocean. TEPCO is frantically catching it and putting it into tanks. But just today, TEPCO announced that they are running out of tank space on site, and eventually they are going to have to release those tanks into the Pacific Ocean. Now they will try to clean up some of the isotopes like cesium. But they have been unable to capture all the strontium. Strontium is a bone seeker that causes leukemia.
So we are not out of the woods. We are far from out of the woods. It will be 30 years before we capture all that nuclear fuel that is underneath that reactor vessel. And until then, it will be surrounded with water that is leaking into the groundwater.
I will keep you informed as situation develops.