The water problem in the United States today is becoming increasingly serious, especially in the western and southwestern portions of the country. It is therefore important that we explore every means at our disposal in order to be able to employ our existing resources as efficiently and constructively as possible. In the search for new tools and new techniques, the potentialities of nuclear explosives have not heretofore been discussed publicly to any great

extent.

During the last several years scientists at the Lawrence Radiation Laboratory in Livermore, California, have been studying possible uses of such nuclear explosive techniques for peaceful purposes, including the improvement of water resources. We are considering both surface and underground water developments, primarily with a view towards achievements for the long run. We are aware, of course, of the problems associated with the control of residual radioactivity; we have therefore undertaken a number of studies to increase our knowledge of the control of radioactivity. While we do not in any way minimize the importance of protecting the public from radioactivity and its effects, we believe that, with further experimentation, we can utilize nuclear explosives in a water development project without significant hazard to either present or future generations. We also recognize that, while we at the Lawrence Radiation Laboratory are expert in the development of nuclear explosives and in the understanding of the interactions between nuclear explosives and the surrounding media, we are not trained in many of the other relevant fields of knowledge. Therefore, we have consulted, and will continue to consult, recognized authorities in engineering, geology, geohydrology, and water resources in order that we may intelligently evaluate sites, experiments, and potential benefits from this program.

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II. NUCLEAR EXPLOSIONS

Ever since the first nuclear explosion, in 1945, nuclear scientists have been looking for ways to utilize, for peaceful purposes, the extremely high energy concentrations available in the atomic bomb. More recently, the results of underground nuclear tests at the Nevada Test Site have shown that changes in both surface topography and the subsurface structure can be induced by appropriate placement of the nuclear explosive.

The first underground nuclear explosion, Rainier, was detonated in volcanic tuff at a depth of 790 feet from the nearest surface. While it was a small event (1.7 kt), as nuclear explosions go, it was large enough to cause profound changes in the material around the shot point (see Appendix I). During the first few milliseconds after the detonation, the ball of hot gas expanded to a radius of about 60 feet, sending a strong shock wave ahead of it, which crushed the material out to a radius of about 130 feet and sent many cracks to more than twice that radius. After the cavity collapsed, in 1/2 - 2 minutes, the failure of successive layers of rock above it resulted in a broken zone (chimney) some 400 feet in height and about 100 feet in diameter. There was no radioactivity detected on the ground surface and no evidence of significant permanent displacement above the shot point.

It is this picture of a completely confined nuclear explosion which leads us to believe that we may be able to make a contribution to the solution of problems in the flow of underground water. For, as an immediate result of each detonation in the tuff, much of the region above the shot point, originally of very low permeability, was transformed into a broken volume through which water would probably flow more readily. At the same time the permeability of the material directly below the shot point and at the sides of the cavity was still quite low. A nuclear explosion in another medium may,

of course, behave differently. But, in favorable areas, it is likely that the permeability of a fairly large region above the shot point can be increased

by a nuclear explosion. We therefore expect that we can break up a relatively impermeable layer of rock to form a conduit to lead water from the surface to an underground area or from one underground site to another.

On October 14, 1958, another underground nuclear explosion (Neptune) was set off. In this event, the detonation of a 110-ton nuclear explosive in volcanic tuff resulted in the throw-out of 45,000 tons of rock, leaving a crater 150 feet wide, 200 feet long, and 40 feet in depth. In this process less than 5% of the gross radioactivity escaped to the surface. It is reasonable, then, to expect that we can create artificial lake basins and channels for water flow by the use of these explosives. Since we can still get useful craters with only a small percentage of released radioactivity, it would appear that the alteration of surface topography to create reservoir sites and infiltration basins is a possibility worthy of investigation.

III. PRINCIPLES OF RADIOACTIVITY CONTROL

One of the most important considerations in the use of nuclear explosives is, of course, the control of radioactivity in order to guarantee public safety. When a nuclear explosive is detonated, radioactive fission products are released and other less abundant radioactive materials are formed by the interaction of escaping neutrons with the surroundings (see Appendix II). The use of thermonuclear explosives and a neutron-absorbing blanket can significantly reduce both the fission product and induced radioactivity. However, the residual tritium from the thermonuclear explosives may further complicate the problem. The isotopes produced in a fission explosion are essentially the same as those produced by nuclear reactors; one kiloton of fission yield produces about the same amount of radioactivity as one day's operation of a 55 megawatt reactor.

There are two different types of radioactive hazards produced by fission products. One kind results from the residual y-radiation field, which, like an x-ray beam, penetrates even massive objects which lie close to the radioactive debris. Essentially no radioactivity is induced in objects irradiated by this field, and, in this residual y-radiation field, the effects produced are proportional to the time spent in the field and to the intensity of the field. The second kind of radioactive effect which can be produced by fission products arises when they are ingested by humans from water and food, so that the short-range ionizing particles are able to cause internal damage. The effects 90 of Sr

are of this nature.

The general radiation field is produced by radioactive materials which reach the ground surface when an explosion is not fully contained (e.g., in the creation of surface storage reservoirs or recharge basins). The most obvious, and the most important, means of controlling this radiation is to

prevent unintentional human access to the radioactive area until the radiation field has had time to decay. In most of the applications so far considered, the decay would not take more than about one year, even if all-fission nuclear explosives are used; during that time, careful monitoring and control of the entry and exit of personnel, material, and water would be necessary. After the radiation field has decayed to a safe value, as determined by measurements of radioactivity, free and unrestricted access could be allowed. No residual y-radiation field of this kind would be produced if the debris from the explosion were not permitted to reach the surface of the earth; even when the explosion is designed to produce a crater or a channel, not more than a few percent of the radioactivity would be found on the surface.

The second type of radioactivity effect, that due to a longer-lived isotope which may be ingested and thus cause internal damage, is a little more difficult to assess. Its magnitude depends strictly on the details of the geology, the ground water disposition, and other characteristics of the specific site of the detonation, as well as on the amount, the nature, and the disposition of the radioactive material. As discussed in Appendix II, most of the radioactivities which are produced in the explosion are trapped within a few feet of the shot point. Since the potentially dangerous radioactivities, in this sense, are 90 those which have relatively long half-lives (e. g., Sr with a 28-year halflife), it must be ascertained not only that the water and the area are safe immediately following the explosion, but that the water will be safe for periods as long as several centuries. Therefore, even though the radioactivities are bound in slag and on the surfaces of rock, which can prevent their reaching the human population at early times, their further behavior must be predicted. Fortunately, it appears that, in some rock and soil types where relatively pure water is in contact with radioactive substances, the radioactive atoms