Science
`Peaceful' Bombs
By JOHN WILLIAMSON IN 1957 the first atomic explosion whose effects were totally confined underground was let off in Nevada The first by the Americans, that is; what the Russians do. they don't always say. A chamber six feet across was made 790 feet below the surface of a hill, by letting into the hillside a horizontal excavation, shaped corkscrew fashion to contain the shock wave, with the bomb at the end of it. When detonated, there was the usual ter- ribly beautiful explosion, though nobody saw it, with a momentary temperature of one million de- grees and pressure of seven million atmospheres, and a suppressed pulse of radiation, including a violent shower of neutrons. In less than a tenth of a second, the chamber was puffed out like bubble-gum to 125 feet in diameter, coated inside with 800 tons of brightly glowing liquid rock. In a few minutes the temperature subsided, the lava began to run down the sides like toffee and drip from the roof, forming 'stalactites' and 'stalag- mites' as it cooled. When solid, the lava set as a glass, and dissolved in it was 65-80 per cent. of the radioactivity produced by the bomb. Gradu- ally the heat and the radioactivity leaked away, and the roof crumbled in, forming a chimney of broken and collapsed rock 400 feet high vertically above the cavity, but not reaching the surface. There was no fallout, no movement of the soil surface, and only a relatively slight earth tremor.
Since the Rainier explosion,' as it was christ- ened, there have been five other underground explosions by the Americans; most of them entirely bottled up, radioactivity and all.
On the ba'sis of these tests, which were all for military purposes and ended, and were mostly in, October, 1958, it can now be planned with con- fidence how far to bury a bomb of a given size so that no radioactivity escapes. General features of the explosion can be predicted: what size cavity will be made, how much energy generated, what temperature reached, how much rock melted, and so on. The Plowshare project was set up in California after the October tests had finished to examine the possible peaceful uses of underground atomic explosions, and the possi- bility of using, for peaceful purposes, under- ground H-bomb explosions, which are altogether bigger, and have never been tested.
Certain ways of using these explosions have been suggested. in sketchy form, of course. One is for brute excavation; removal of large amounts of. rock to help build harbours or canals, or to create big new water reservoirs. Another is for converting unprofitable oil deposits into work- able ones, for instance by heating heavy oil to reduce its viscosity so that it may be pumped up, or by running small oil ptiols together to make one large profitable pool. A similar idea is the con- version of unworkable coal into liquid products and gas that can be used. The ,host daring idea is to use the heat generated in some way to run a power station. The difficulty about this is that the heat was rapidly dissipated in the tests in 1958, chiefly due to the, high water content (15-20 per cent.) of the rock. If some way could be found to preserve the hot spot around the bomb.for some years, then it could be used to drive turbines and produce electricity. This is possibly where the H- bomb comes in, for at the depth at which such a fusion bomb would have to be buried, over half a mile, the rock is warm anyway, and this would help to reduce the rate of cooling. With an im- pervious dry rock at this depth, it has been cal- culated that one H-bomb explosion underground would keep an average-sized power station running for fifteen years. A less practical use for these explosions is the prosecution of pure re- search, such as measuring the thickness of the Antarctic crust. The interest for physicists lies in the shower of neutrons emitted, which have a high energy, far greater than is provided by any exist- ing method, so that when these bombs explode. laboratory' experiments otherwise impossible can be performed.
They will be used to bombard radioactive metals in order to carry out certain techni- cal measurements. Radiation, apart from neutrons, from this bomb will also be studied. So far, so good, it seems. Unfortunately, dis- senting voices have been raised in some quarters, naturally enough. The peaceful use of nuclear explosions is a different fish from the peaceful use of atomic energy, merely. Vor one thing, the health and safety hazards are uncertain. Water supplies may be contaminated. Perhaps even more opposition. however, is •prompted by political fear, particularly the explosions of an alien country, no matter how much they are the beating of ploughshares and pruning hooks. What guarantee has Mr. Khrushchev (or you and I) that the bombs exploded under the Alaska coastline are not military weapons? And vice versa?
What was significant about the sudden rush of underground explosions in America in October. 1958, was not simply that they were an attempt to finish a testing programme before the expected ban when the talks about inspection and control began in Geneva in that month. In fact, what was being tested? The bombs were mostly smaller than Rainier, and at varying depths. What was being tried out was various ways of muffling these ex- plosions. by design of the chamber and choice of rock formation. Rainier, the prototype, was a noisy explosion; its murmurs were picked up 2,320 miles away, in Alaska. So, armed with the data from Rainier, US negotiators went to Geneva with an appropriate plan for an inter- national inspection system, while, that same Octo- ber, someone had already planned several 'quiet' explosions. What kind of situation was this? Were the negotiators disingenuous? Were they misinformed deliberately about the plan to try quiet explosions (presumably having the expec- tation of some success)? Or were the October ex- plosions a rush of last-minute ideas which turned up surprising results they didn't have time to telephone to Geneva? Since an explosion needs long planning, and its results are up to a point predictable anyway, the last supposition is at first sight the most suspect. What is interesting is that the Russian scientists at Geneva were awake to all this, and while the American wool was being wrapped round their eyes, they checked the figures and said they were wrong, which they were. Which suggests they had figures of their own already.
The Americans have had three particular underground explosions planned for some time, for purely peaceful purposes, as part of the Plowshare programme. One is in Alaska, where live heavy simultaneous explosions are planned for specific sites in an attempt to build a harbour. Another project is to explode a smallish bomb under the oil-bearing Athabaska Sands • in Alberta. The sands are expected to fall into the hot cavity and form a pool of oil which can be pumped up, which is at present impossible. It is expected that the oil will not be radioactive. A third project is to explode a small bomb in a bed of salt in Carlsbad. New Mexico. The purpose of this is to see how good a heat trap the melted salt is, and to see if it is an efficient heat reservoir that can be tapped to work turbines, probably by piping gas through it and using the heated gas for power.
*. . . I really feel we're getting Aomewhere at lust!'
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