The “Lost Atomic Bomb” And Its Consequences

Press, Volume XCVII, Issue 28552, 3 April 1958, Page 10

The “Lost Atomic Bomb” And Its Consequences

Atomic explosions up to 10 times the power of the atomic bombs dropped on Hiroshima may be an everyday occurrence within two vears almost anywhere in the United States under a civilian programme being pressed by the scientists of the United States Atomic Energy Commission.

The programme calls for harmless underground detonations which the scientists are convinced will bring immeasurable benefits to national policy, private industry and the general public as well as atomic weapon developments.

The following is a statement made by Dr. Willard F. Libby, a member of the Atomic Energy Commission, to the Disarmament Sub-committee of the Senate Foreign Relations Committee on the “lost atomic bomb" and the possibility of detecting underground explosions. (The statement was printed in. the “New York Times” on March 14): Last fall, on September 19, we fired a bomb underground in Nevada. This was a small bomb. We made it small for the reason that we were afraid of earthquake shocks, although all the theorists told us that the shocks from the earthquakes -would be minimal, as they were.

“Nevertheless, we wanted to be safe, so we picked the softest, spongiest mountain we could find, and it consisted of tufa volcanic ash which was partially congealed and was quite porous and therefore like a sponge, more or less. We put the bomb 800 feet down in this mountain and its yield was about as small as has been fired, that is 1.7 kilotons.

“Well, we fired it on September 19. We saw that the mountain jumped about six inches, but our geiger counters showed no effects and we were worried that there might be some fissures develop so that the radioactivity might get out. “Among the radioactive products of a bomb are some gases, krypton, for example, and zenon, which have no chemical formula. These things are permanent gases but we could not even find those. After waiting for a few days we started drilling to find this bomb, and we kept drilling. “We drilled straight down. We had in mind the notion that the bomb would have melted a glob of rock and the energy, of course, is quite sizeable, and we were afraid that when we got in and hit this, that something horrible like an explosion would occur. So our drill crews were very cautious about it, but they kept drilling away. When they got about half way down into the mountain, about 400 feet, they found a cavity. The drill machinery dropped about 50 feet, and in this cavity they found a little whiff of radioactivity.

Kept on Drilling “Then they kept going and they found that from here on in it was impossible to keep the drilling water going. The drilling water seemed to just flow away to infinity. There was a porosity in the rock which was not there in the mountain before. We kept going until we got right down to ground zero where the bomb was, and we still nad not found any more except this little whiff of radioactivity that we found about half or two-thirds of the way down. So the problem at that point, this was about two months after the bomb was fired, was what in goodness happened? Where was this bomb? We knew perfectly well that it had gone off and we knew the radioactivity was trapped in there, so we could not find it. We had put the bomb in the mountain by taking a tunnel 2000 feet long into the side of it. It isn't a mountain. It is a mesa, and so we went in the tunnel, and of course we looked in the tunnel before, but the tunnel was closed out to about 200 feet from the bomb site, and we had rather expected that the tunnel might be closed farther out by the explosion. The tunnel was straight for about 1600 feet and then made sort of a spiral and we put the bomb in the centre of this spiral. Well, when we couldn't find the bomb by drilling downward, then we went in the end of the tunnel and started drilling horizontally, pointed right at the bomb where the bomb had been. Well, we got in and about 50 feet from where the bomb was known to have been located, we found a little bit of radioactivity again, quite a little bit this time, but it was only in a layer about so thick [indicating]. Then we kept drilling, and again we got right to ground zero, and no bomb. Where the Bomb Was Then we sat down and did the thinking that we should have done two months before, and figured out where it was.

To make a long story short, what had happened was that the bomb had blown itself a bubble of gasified vaporised rock, and this bubble was about 110 feet in diameter and about 55 feet in radius, and the skin of the bubble was molten rock about four or five inches thick, and in this molten rock was all of the radioactivity of that bomb, even the gaseous products were trapped in this molten rock. Then it cooled. Now the shock wave had gone beyond where the bubble expanded and had broken out to 130 feet, had pulverised the mountain, so what happened was that the rock that overlay this thing had no more strength, and when the bubble cooled, when the heat cooled to the point where the pressure of the gas inside the bubble would no longer support the weight, which of course was just a few seconds afterwards, the thing collapsed of its own weight So what we were looking tor in there was a broken egg. really an egg shell which had been crushed, and so our bomb fragments were entirely in the form of a sort of a bowl underlying the ground zero point. Then we drilled from the end of the tunnel, we went down at a slant and sure enough, we found the hot rock. Now the rock was black, dark coloured. You could pick it out visually. That is. the radioactive material is entirely in rock which you can visually distinguish from the rest of the mountain. You can. of course, do it with radio instruments very easily, because it is intensely radioactive, but there are a number of things you can learn from that.

First, you can fire bombs in a way where the radioactivity does not come out Second, you can crush an enormous quantity of rock. This little, tiny bomb, 1.7 kilotons—l don’t know that you should ever call any bomb tiny, but I mean on a relative scale this little fellow—broke 400,000 tons of rock, crushed it up. We found about two-thirds of the energy released in the bomb clustered around the site. What had happened was that the rock was porous and there was water in it, and whereas we were rather expecting to find some molten rock when we got down in there, we didn’t. The rock had been cooled by this water that would make steam, and the steam would go out and heat up some neighbouring rock, porous structure, so we found that this whole sphere out to a diameter, a radius of about 130 feet and weighing about 400.000 tons was heated up by something like 40 degrees F„ I believe the number is, by the heat of this bomb.

Great Potentialities From all this, I think we learn that we have great potentialities in nuclear explosions themselves, the possibilities of making atomic power. If we had a dry mountain the conductivity of the rock is practically zero, that is a hot rock, a molten rock will conduct heat, but a hot rock that is solid will not. This is what firebrick is made of. That is the way you insulate furnaces, and the temperature gradient in the earth shows this. So if we have a dry mountain, we should be able to maintain the heat at a sufficient concentrated form so that we could pump water down in there and make steam.

Now we have in mind doing just this kind of thing. We call this “Project Plowshare,” and we are going to try to develop the non-military or peaceful use of atomic nuclear explosions, of which one is atomic power. We have others. We know, for example, from our experiences already that we can make harbours. You have perhaps all seen some of the cavities we have made in the Pacific. Of course, these at the present time could only be made in remote areas for the simple reason that the fall-out is so bad that we would not dare do it, though if we use some of our cleaner bombs, the fall-out is much reduced, and so this points up further developments of the weapons of the nuclear test devices will allow us to clean up the smaller ones and then we may be able to move earth even in more populous areas. The cost of moving earth by this device, except for the fall-out, is pretty low.