Plutonium processing chain-reaction

The Natural Reactor. Some two biUion years ago, uranium had a much higher (ca 3%) fraction of U than that of modem times (0.7%). There is a difference in half-hves of the two principal uranium isotopes, U having a half-life of 7.08 x 10 yr and U 4.43 x 10 yr. A natural reactor existed, long before the dinosaurs were extinct and before humans appeared on the earth, in the African state of Gabon, near Oklo. Conditions were favorable for a neutron chain reaction involving only uranium and water. Evidence that this process continued intermittently over thousands of years is provided by concentration measurements of fission products and plutonium isotopes. Usehil information about retention or migration of radioactive wastes can be gleaned from studies of this natural reactor and its products (12). 

When the Plutonium Project was established early in 1942, for the purpose of producing plutonium via the nuclear chain reaction in uranium in sufficient quantities for its use as a nuclear explosive, we were given the challenge of developing a chemical method for separating and isolating it from the uranium and fission products. We had already conceived the principle of the oxidation-reduction cycle, which became the basis for such a separations process. This principle applied to any process involving the use of a substance which carried plutonium in one of its oxidation states but not in another. By use of this... 

Fission weapons or bombs They derive their power from nuclear fission when heavy nuclei such as uranium (U) or plutonium (Pu) are bombarded by neutrons and split into lighter elements, more neutrons and energy. The newly generated neutrons then bombard other nuclei which then split and bombard other nuclei and so on. This process continues and leads to a nuclear chain reaction which releases large amount of energy. These are also historically called atomic bombs or atom bombs or A-bombs. 

The discovery of nuclear fission in 1938 proved the next driver in the development of coordination chemistry. Uranium-235 and plutonium-239 both undergo fission with slow neutrons, and can support neutron chain reactions, making them suitable for weaponization in the context of the Manhattan project. This rapidly drove the development of large-scale separation chemistry, as methods were developed to separate and purify these elements. While the first recovery processes employed precipitation methods (e.g., the bismuth phosphate cycle for plutonium isolation). 

The chemists worked out the process for separating the plutonium from uranium and from the very radioactive fission products which resulted from the chain reaction. 

Experiments on this ultra-microchemical scale were performed to test the chemical process for separating the plutonium produced during the war by the chain reaction at Hanford, Washington. This process used bismuth phosphate as a carrier material, and it was conceived and worked out in... 

Groves moved on to Berkeley more impressed with their work than his Met Lab auditors realized. I left Chicago feeling that the plutonium process seemed to ofier us the greatest chances for success in producing bomb material, he recalls. Every other process. .. depended upon the physical separation of materials having almost infinitesimal differences in their physical properties. Transmutation by chain reaction was entirely new, but the rest of the plutonium process, chemical separation, while extremely difficult and completely unprecedented, did not seem to be impossible. ... 

Breeder reactors convert nonfissionable into fissionable Pu. The material used for fission is a combination of U-235 (which undergoes fission in a chain reaction) and the more common U-238 isotope. Excess neutrons from the U-235 fission are absorbed by the U-238, converting it to the fissionable plutonium isotope Pu-239. The chemical and physical properties of Pu-239 make it very difficult and expensive to handle and process. 

Np. The isotope Np is formed in considerable quantities in reactors, by the nuclide chains initiated by (n, y) reactions in and by ( , 2n) reactions in Neutron capture by Np leads through Np to Pu, which is the principal alpha-emitting constituent of plutonium in power reactors. To produce Pu for use as a heat source for thermoelectric devices, neptunium has been recovered from irradiated uranium to form target elements for further irradiation in reactors. Commercial processes designed for this recovery are discussed in Chap. 10. 

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