FREQUENTLY ASKED QUESTIONS about Chernobyl.....the nature of radiation....the worst that could happen in a modern reactor accident....and more....

These Q & A's are from a FRONTLINE interview with Dr. Charles Till, a nuclear physicist and Associate Lab Director at Argonne National Laboratory West in Idaho.

Q: What is the basic material or fuel that makes nuclear energy possible?

A: It's always uranium. It's the fission of uranium.

Q: What is uranium, and where does it come from?

A: Uranium is simply a metal. It's found everywhere in the earth's surface. It's found at two parts per billion in the oceans. It's concentrated, like all the metals, in deposits here and there all over the earth. It looks something like lead. It's heavy like lead. It has a mild amount of radioactivity associated with it, but nothing like radium, for example, which is also scattered throughout the earth's crust.

Q: What is the special property it has?

A: Well, the special property is that if it is bombarded with neutrons, then the uranium nucleus will split in two, and with that a large amount of energy is released in the form of heat. And this is called fission.

Q: And why is that important? Because this amount of energy is large?

A: It's millions of times as much as is released in burning (fossil fuels). And so what that means is that if you do it properly, a very small amount of material can give you a vast amount of energy. And hence, a small amount of uranium can give you a very great deal of energy. That energy can be converted to electricity.

Q: So take us through the principal ways this energy's been harnessed, both in bomb making and in a controlled reaction.

A: In a controlled reaction you assemble uranium in a way that allows a very stable, very steady reaction. The heat gets produced, then is used to boil water and produce steam, and that steam then produces electricity through turbines, same as any other electrical generating plant. There's nothing very exotic really about it. The trick in all of it is to assemble that uranium in a manner that is the safest possible, and uses the resource most efficiently. And you want to see the waste from it minimized and be as safe as possible.

Q: So what happens after a reactor's run for 18 months, with these uranium pellets? What are you left with?

A: Well, the uranium is in the form of pellets, and typically, what you have of the original fuel that you put in there is only a very small percentage of it has been used up, perhaps one, two, three percent after a year. And the fissioning process has made that fuel rod very radioactive. Much of that radioactivity goes away within minutes, some after hours, and some after days. But you're left with a considerable residual amount of radioactivity. Now, some of those materials could be reused. Some of the radioactive materials could be reused if you recycle the fuel. For today in the U.S., the policy is no recycling. And so you're left with whatever's there.

Q: What is the key product created from uranium?

A: The main useful isotope, and the one that has become controversial for reasons I'm not sure I totally understand, is plutonium.

Q: And what is plutonium? Does it occur naturally?

A: Plutonium is simply a material that is very like uranium, being produced from uranium. It's produced by the absorption of a neutron in uranium, and you get this new metal which has been called plutonium. Its properties are not dissimilar to one of the isotopes of one of the kinds of uranium that exist in the earth's crust. It is fissionable, like the fissionable isotope of uranium. That is to say, you could make a reactor out of it, out of plutonium.

Q: So, most of the uranium that you get out of the ground doesn't have this magic fission property?

A: Correct. The amount of fissionable uranium is 0.7 percent of all natural uranium. In all the uranium in the earth's crust, only about 0.7 percent of it is fissionable.

Q: Now, if all you did was fission that small amount and throw the rest away, then you'd be dealing with a relatively scarce resource?

A: Yes. You're dealing with a relatively scarce resource.

Q: Are you saying that bombarding old uranium with neutrons creates a new element?

A: Yes. Yes, exactly so. While the uranium is fissioning inside the reactor, some neutrons are caught by the non-fissioning isotope of uranium, which is 99% of it. And some small percentage of that converts to plutonium. Plutonium is as fissionable or more fissionable than the uranium isotope that is the useful isotope. So that one can see that if you arrange this properly, that the non-fissionable isotope of uranium can be made fissionable, and then fissioned to produce energy. And if you recycle, you will eventually be able to use 100% of the uranium, and not the less than one percent that is used now.

Q: So part of the original dream was that plutonium was a very useful material?

A: More than useful. It is the avenue to the vast amounts of electrical energy that are possible from nuclear energy. It is through plutonium that the future opens up.

Q: What is plutonium? Is it a metal like uranium?

A: Plutonium is, in fact, a metal very like uranium. If you hold it [in] your hand (and I've held tons of it my hand, a pound or two at a time), it's heavy, like lead. It's toxic, like lead or arsenic, but not much more so.

Q: How can plutonium harm you?

A: You have to eat it in order to harm yourself with it. It is radioactive, naturally. Radioactive, but much less so than radium, for example, which is scattered again all over the earth's crust. So it's not a very frightening material.

Q: So you say you hold it in your hand. What about the radiation that is emitted by plutonium?

A: The radiation from plutonium tends to be very easily stopped by any kind of shielding around the plutonium. A pair of gloves, paper. Certainly, a thin film of steel will stop the radiation from plutonium, so that it's perfectly safe.

Q: Is the skin on your hand is enough to shield yourself from plutonium's radiation?

A: The skin on your hand is probably sufficient to stop most of it.

Q: We've all heard that it's the most toxic substance in the world. Isn't it?

A: Well, I think it's absurd. It's not toxic. As I say, it's no more toxic than any other heavy metal, and its radioactivity is very considerably less than many other things that are on the earth's surface. It's an absurd statement.

Q: Because plutonium's fissionable, can it be used as bomb material?

A: Now, that must be taken seriously. What one can say is that the handling of any fissionable material, including the fissionable isotope of uranium, must be done with care and with safeguards. If you have fissionable material, you have the possibility, difficult though it may be -- or next to impossible in the case of some forms of plutonium. But there is a possibility of making usable material. So there is where the attention needs to be focused. But it's a perfectly handle-able situation.

Q: Can't plutonium produced in a reactor get into the wrong hands, and somebody with an elementary chemical training turn it into a bomb?

A: Well, it's false. The plutonium that you get from a reactor is a form of plutonium that's extraordinarily difficult to work with. And a potential bomb manufacturer would have to have a sophistication matched by the great national laboratories of the land, in order to make any kind of a satisfactory weapon out of it at all. One must realize that to use plutonium for weapons, that in those countries that have done that, including our own, that an isotopically pure form of plutonium is produced precisely for that purpose, precisely for the purpose of making weapons. If you have plutonium out of a reactor, you do not have those possibilities open to you. The material is hot. The material is highly radioactive. It's dimensionally unstable. It's all kinds of things that the bomb designer does not want to have to deal with at all. And someone with a chemical background could possibly separate the material. But having separated it, there would be a very long way to go.

Q: How is the isotopic form unsuitable for weapons?

A: Yes. Plutonium is different from uranium. Uranium has really those two isotopes. And let me call them by their names, uranium-235 and uranium-238. That's simply two different isotopes of the same metal. 235 is fissionable. Plutonium, when it's produced in a reactor, the first isotope you get is plutonium-239. That comes from the uranium-238. Almost immediately after that isotope will absorb another neutron and become plutonium-240. At least, some fraction of it will. And that is a highly unsatisfactory isotope to the weapons designer, because that gives off a lot of neutrons itself, and makes it very difficult to trigger any kind of an explosion effectively. But it goes right on. It goes to plutonium-241, to plutonium-242, and that whole mixture of isotopes of plutonium is exactly what the bomb designer does not want. He wants pure plutonium-239. That comes from reactors that are specially set up to produce the isotope plutonium-239, and not all of the mixture of isotopes that come out of the nuclear reactor.

Q: So to make a bomb, you'd have to then chemically separate the good plutonium?

A: You always will chemically separate the plutonium. The key point is that if the plutonium has been produced in a weapons production facility, production reactor, then the plutonium that's in that fuel will be almost pure plutonium-239. It will also have, of course, a lot of the uranium-238. And then a chemical separation must be done. But the plutonium that you get out will be pure plutonium-239. Contrast that with the reactor situation, where when you make your chemical separation, you will get plutonium, but that plutonium will be a mixture of plutonium-239, 240, 241, 242, that is highly undesirable for a weapons maker.

Q: Is the scenario that commercial reactor plutonium could be stolen by terrorists and made into bombs realistic?

A: Very far-fetched. It's very far-fetched. If you look at the weapons programs of those countries who have produced weapons, you will find most of them have probably tried using plutonium with mixtures of isotopes, probably never as dirty a mixture as you find in reactor plutonium today. But tried to see whether they could make effective bombs with not quite so pure plutonium-239. If they tried it once, I think you will find they never did it again. I think perhaps the U.K. tried it twice but after that, went right back to trying to assure that the plutonium was as pure 239 as possible.

Q: How significant was the decision by this country to not go the recycling route?

A: Well, I think that the importance of that decision cannot be underestimated. It was the decision that changed, for our country anyway, and then whatever our influence may be on the rest of the world, the orderly progression of nuclear energy for the future of our nation. All the factors were brought together in that decision by groups like the anti-technology people, the people who are seeking to use nuclear as a political platform, or anti-nuclearism, the arms control people and so on. When all of those factors were there, and when the decision was made not to recycle, so many implications followed. So all of a sudden we had a nuclear waste problem. Volumes of nuclear waste from our present reactors, but good way to deal with it. By recycling, you deal with it very adequately. Without recycle, you don't. All of a sudden, nuclear energy had only a finite lifetime facing it, because without recycle, the uranium itself could not be (used up). All of a sudden, the American influence on nuclear energy around the world lessened, because the U.S. was taking that path that other countries either wouldn't or couldn't follow, for their own energy self-interest. And so on. It was a tremendously important decision.

Q: Why does not recycling or reprocessing make the waste issue worse?

A: If you look at nuclear waste from the point of view of the long-lasting nature of the nuclear waste, or any of the things that the general public would be encouraged to worry about, always it's the plutonium and other isotopes in the nuclear waste that is of concern. And in a sense, they should be, because they are the long-lasting isotopes that, if they get into the drinking water or into the air, could cause real concern.

Q: And they last a long time?

A: They are cancer-causing chemicals.

Q: What is a half-life of plutonium?

A: Well, plutonium-239 has, for example, a roughly 25,000-year half-life. That is to say, half of it will have decayed to something else after 25,000 years, approximately. And that's a good long time. And the other isotopes that are similar to that, some have longer half-lives, some of them shorter. The point is that they are the most toxic elements in the waste. And paradoxically, they are also the most useful, because they are all fissionable. So they can be used to produce energy. But if they are there in the waste, they represent a long-term hazard that people can legitimately be concerned about. And those states that are being asked to accept the nuclear waste can legitimately be concerned about that. You know, I think again it's a handle-able problem, but it's a problem that needn't be there, for if you recycle, you separate out exactly those elements and use them in your reactor. You produce energy with them and they're gone. And the nuclear waste that is then put in the ground has a life of perhaps a few hundred years, and all of the really toxic materials are gone. So it totally changes the character of the nuclear waste problem.

Q: What is the nature of radiation? Is it that people have no way to experience it?

A: No, it isn't. And radiation, of course, to most who work with it is a very workaday kind of thing. The nature of radiation is that it requires a good bit of it to do you any harm. The nature of radiation is that you can detect absolutely insignificant amounts of it, extremely easily. The nature of radiation is that if you don't choose to detect it, you have it falling on you from everywhere you are on the earth's surface, in amounts that are probably 100 times or 1,000 times more than you would ever get from living near a nuclear plant.

Q: Where does most natural radiation come from?

A: Well, the natural radiation is mainly cosmic rays interacting with the earth's atmosphere, and we get a good bit of radiation on the earth's surface. The closer you are to the cosmos, the more radiation you get. So that if you're up in an airplane, you'll get considerably more than on the Earth's surface. Or people living at 5,000 feet, as I do, will get more than people living at sea level. But it's a part of the human environment just as air is, or anything else. It's most unremarkable.

Q: Why haven't experts been able to demonstrate to people that radiation is a natural phenomenon for which there's no escaping?

A: Well, I'm not sure. I'm not sure that we are always able to convince people of our views, even though they may be correct. I think it requires a little bit of scientific background, probably, to be able to assess whether a statement that's made (you'll forgive me) on television is to frighten you for some political or other purpose, or whether it's there to provide you with information.

Q: Do you think most people trust the DOE nuclear physicists, the utilities?

A: No. Of course they don't. And that, I think, is somewhat understandable. But why the anti-nuclear folks, who say such extreme things that on the face of it one would question, even one who knew nothing about the subject, why they would have credibility, that does puzzle me.

Q: Do you think basically the safety record for nuclear power plants is good or bad?

A: I think the safety record is wonderful. If you look at reactors in this country, no one has been killed from the nuclear part of the nuclear plant in this country, ever.

Q: So how does nuclear power compare to other industries?

A: It compares very, very well. The nuclear industry is much safer than most industries. Much safer in the sense of the people that work in the plant, and much safer as far as any effect on anyone around the plant is concerned. They key event that everyone remembers is first Three Mile Island in this country, which happened in 1979, ... where television was absorbed for several days by that accident. But when you really looked at it, although it was a tragedy that the plant itself was destroyed, there were no identifiable injuries except psychological. People feared that there would be problems.

Q: Was Chernobyl a serious accident?

A: Chernobyl was the most serious accident, in my view, that a reactor could possibly have. It was a very large plant. It had been operating long enough that it had a large inventory of radioactive material and, it blew up. It was opened to the atmosphere for days. Fire, plumes of material, radioactive materials. The people who were asked to deal with the fire obviously had to be subjected to, in the crude way that the authorities responded to it, killing amounts of radiation. Some 30 or 40 of them did that, at an awful price. But contrary to the common knowledge that is simply not so. There have been very few, or in fact, only one identifiable source of deaths from that Chernobyl accident. And they are thyroids in children.

Q: Was Chernobyl as bad as it could get?

A: That's as bad an accident as you can get from a nuclear plant. And worse than any accident in a modern nuclear plant could possibly be. The point is that that reactor was on fire for days and days and days, with radioactive material going up into the air. But it was the crudest kind of reactor, which the Soviets thankfully have stopped building.

Q: Is it fair to compare American reactors to the one at Chernobyl?

A: It's completely unfair. It's like comparing the Stanley steamer that's going along at 150 miles an hour to a present day car with all the safety features a modern car has. And that Chernobyl plant was a very crude plant, was operating badly. It had the worst possible accident. And yet the number of identifiable deaths from it are really only a handful. And even the children who were affected by it, some few dozen, those could have been avoided with iodine tablets.

Q: Can a nuclear plant explode like a nuclear bomb?

A: Well, the worst that can happen in a modern nuclear plant is not even a fire. And it certainly isn't an explosion. It can't blow up like a weapon. It just can't. If I could make a comparison, your yule log in your fireplace versus gunpowder. I mean, you cannot blow up a nuclear plant like you can assemble uranium in a weapon to give you a tremendous explosion. It's just cannot happen. And those people that suggest that it can aren't doing the public much of a service.

Q: So what is the worst that could happen in a modern commercial nuclear power accident?

A: The worst that could happen probably would have been a release of fission products from the steam. You would have the fission products from the fuel. The fuel has melted, and so you've released the fission products, and perhaps you get some kind of steam that carries some fission products out of the plant, and people would be exposed to that. It wouldn't be the explosion itself, or any explosion that would cause problems.

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