The electromagnetic process they implemented at Oak Ridge entailed a number of special hazards, General Groves explains (in Now It Can Be Told: The Story of the Manhattan Project), because uranium is toxic as well as radioactive:
Some of the raw materials were also extremely difficult to handle. High temperatures and pressures were involved and many irritants such as phosgene had to be used. Liquid nitrogen was used in large quantities at a temperature of –196° Centigrade. Huge amounts of electricity were used throughout the process. Each control cubicle, for example, of which there were ninety-six for each alpha track and thirty-six for each beta, consumed about as much electricity as a large radio station.
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We had eight fatal accidents in all of our plant operations through December, 1946. Five people were electrocuted, one was gassed, one was burned and one was killed by a fall.
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Despite all the difficulties that had to be overcome, the first shipment of enriched uranium was sent to Los Alamos in March, 1944, just a few days more than a year after the construction of the plant was begun.
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The chemical side of the electromagnetic process, in fact of the entire project, has often been treated as a simple auxiliary to its more eye-catching atomic physics aspects. Actually, chemistry was the beginning and the end of each of the separation processes. Production efficiency could be won or lost in chemistry, as well as in physics. Each was indispensable.
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The gaseous diffusion process, later termed the K-25 project, was a large scale multistage process for the separation of U-235 from U-238 by means of the principle of molecular effusion. The method was completely novel. It was based on the theory that if uranium gas was pumped against a porous barrier, the lighter molecules of the gas, containing U-235, would pass through more rapidly than the heavier U-238 molecules. The heart of the process was, therefore, the barrier, a porous thin metal sheet or membrane with millions of submicro-scopic openings per square inch. These sheets were formed into tubes which were enclosed in an airtight vessel, the diffuser. As the gas, uranium hexafluoride, was pumped through a long series, or cascade, of these tubes it tended to separate, the enriched gas moving up the cascade while the depleted moved down. However, there is so little difference in mass between the hexafluorides of U-238 and U-235 that it was impossible to gain much separation in a single diffusion step. This was why there had to be several thousand successive stages.
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Without question the most serious problem that confronted us throughout was our inability to produce until late 1944 the barrier material which was the heart of the process. This prevented the orderly installation of the production equipment. It meant that before the first unit could be put in operation, some $200 million had been spent on construction and on the purchase of special equipment, and most of this had been done before we knew even that a satisfactory barrier could be made in the quantities we would require. Yet in spite of this major unknown factor, we had to press ahead with the construction of one of the largest industrial plants ever built, comprising over forty acres of floor space.
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The Oak Ridge plant was a first in every sense, and its design, involving many acres of barrier, was based on this small piece less than two square inches in area. Even this practical foundation soon disappeared when it became known that the material used in the first filter could never be employed in the main plant.
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Finally, after warning us that they were so overloaded with war work that he did not see how they could possibly undertake it, he consented to our talking with his chief engineer. We were amazed when, after we had described in some detail the exacting performance specifications, he replied, “Yes, we can do that. We have already manufactured pumps of the same type, but of course of much smaller capacity.” The contract was accepted and perfectly performed.
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In our hotel rooms we talked at some length about another design problem: how to handle a breakdown within a particular unit. In the course of the discussion, I expressed surprise that it was thought to be a problem, since all that was necessary was to cut out the particular unit that had broken down. The difference between the makeup of the gas varied from diffuser to diffuser so slightly as to be un-noticeable and almost unmeasurable, and I asked how the diffusers could ever tell the difference. That casual question immediately suggested the answer. As so often occurs, it was a case of a simple solution occurring immediately to someone who had not been struggling for months with the problem.
To minimize the effects of gas corrosion, it was first proposed that we use solid nickel for the some hundred miles of process piping. K. T. Keller, the head of the Chrysler Corporation, which was to produce the diffusing units, pointed out that our demands in that case would exceed the entire nickel production of the world, and insisted that heavy nickel plating on the inside of the larger pipe, four inches and above, was feasible. To attempt to heavily nickel-plate the interior of the quantity of pipe we needed was an unprecedented undertaking, but it was solved by a small manufacturer in Belleville, New Jersey, the Bart Laboratories. They developed a novel method in which they used the pipe itself as an electroplating tank. The pipe was rotated during the operation in order to obtain a uniform thickness of deposit. Their success eliminated what otherwise would have been a most difficult situation.
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We had to be absolutely sure that in the hundreds of miles of piping the total leakage of air into the system, particularly through the welds, would not exceed that which would enter through a single pinhole. This problem was solved by industrial engineers. By using helium gas with an improved mass spectrometer, we were able to detect all leaks before the individual piping assembly was installed, and because we could not permit any leakage, no matter how slight, we could not tolerate normal commercial shop welding of the pipe connections, so special welding techniques had to be developed.
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The cleaning and conditioning of equipment prior to installation was vital and the closest practical approach was made to surgical conditions. This involved the complete removal of dirt, grease, oxide, scale, fluxes and other extraneous matter. Any such material, even in small amounts, could very well have caused a complete failure.
The cleaning methods were based on procedures developed by the Chrysler Corporation. The individual steps were not too unusual in industrial practice, but the combination of all of them, their rigorousness and their application to the thousands of pieces of equipment were unheard of.
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All workers changed into clean outer clothing from head to foot upon entering a restricted building.
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Everything possible was done to eliminate dirt and dust. Vacuum cleaners were used instead of brooms, and dust mops were used in order to avoid raising dust by dry sweeping.
TNT looks like butter, but is poisonous.
In the public consciousness, TNT looks like red sticks of dynamite, not yellow blocks: