Nuclear Explosions Underground

Press, Volume XCIX, Issue 29228, 11 June 1960, Page 10

Nuclear Explosions Underground

[By Dr. MICHAEL J. BUCKINGHAM, School of Physics, University ot Sydney]

Whether summit conferences succeed or fail, everyone hopes that satisfactory disarmament agreements can be reached. Many suppose that, if such hopes are realised, the world will see no ■more nuclear explosions. Is this, however, a necessary or even desirable consequence of such happy agreements? • In the event of complete and total world demilitarisation we . would certainly not desire an end to chemical explosions. In fact, much more conventional explosive is used for mining and engineering purposes than for military ones. If nuclear explosives are more efficient than chemical ones for some military purposes, perhaps this is true for peaceful uses as well

The largest peaceful explosion on record in the Western world was used in 1957 for the removal of Ripple Rock, a dangerous obstacle in a navigable channel near Vancouver. This was a great success and involved a conventional charge of 1300 tons —in nuclearage language, over one kiloton equivalent Nuclear explosions much smaller than this can be made, although it is in large sizes that their full effectiveness is achieved. Vast Potential The possibilities exisit for “geographic engineering” on a scale unprecedented in the past. In fact, unsubstantiated newspaper reports in the Soviet Union have already claimed the use of nuclear explosives to “move mountains.” The possibilities include excavation of artificial harbours, power production, underground water-storage basins, extraction of oil from shale or sand deposits otherwise un workable, and many others. These activities would be confined to sparsely settled areas and would have to be subject to the most stringent safety precautions.

The principal danger, and one that does not arise in the case of even the largest chemical explosion, is, of course, from radiation —both neutron-induced radioactivity in the surroundings and

fall-out A fully contained explosion (one not breaking through the earth’s surface) can be achieved by detonation at sufficient depth, thus avoiding any fallout hazard and confining the induced radio-activity. The latter is mostly held, in this case, in the glass-like fused rock surrounding the centre of the explosion. This rock is vaporised in the first instants after detonation and then condenses and solidifies under pressure, holding the radioactive atoms in a relatively harmless state.

The depth required for containment is quite great however, making this approach not very useful for, say, harbour construction. A one-megaton (one million tons) explosion would need a depth of perhaps 3000 feet; a one kiloton about ten times less.

In any case, thermonuclear (fusion) explosives would be preferable to fission ones, the fallout being much less for the same power. The danger in the case of fusion arises from the neutionh produced and it is possible to absorb neutions harmlessly in suitable materials, although it would be impossible to avoid some radio-active contamination. Economic Advantages Unfortunately much of the information concerning nuclear ex-* plosions is still secret, but the Americans have released some, including data concerning a onekiloton charge set off 50 feet below ground in Nevada. This explosion resulted in a crater about 300 feet in diameter and 90 feet deep, involving the removal of 100,000 cubic yards of material. To excavate a hole this size might cost as much as it would by conventional means, but one a hundred times bigger would cost perhaps one million pounds by thermonuclear explosive as against more than ten million pounds by ordinary methods. This illustrates the very great economic advantages that exist in the case of really large-scale enterprises. Provided it proves possible to control the dangers inherent in playing with fire on this scale, many giant projects may be successfully completed that would otherwise be quite impossible.— Associated Newspapers Feature Service.