Fission Processes

Reactor Subcritical (RS) scram lenninalion. >t ihe fission process... 

Fermi began to assemble a nuclear pile in a squash court under the football stands at the University of Chicago. This was really the first nuclear power reactor, in which a controlled, self-sustaining series of fission processes occurred. The controls consisted of cadmium rods inserted to absorb neutrons and keep the reactor from going... 

The main drawback to nuclear power is the production of radioactive waste. Spent fuel from a nuclear reactor is considered a high-level radioactive waste, and remains radioactive for a veiy long time. Spent fuel consists of fission products from the U-235 and Pu-239 fission process, and also from unspent U-238, Pu-240, and other heavy metals produced during the fuel cycle. That is why special programs exist for the handling and disposal of nuclear waste. 

When a uranium-235 atom undergoes fission, it splits into two unequal fragments and a number of neutrons and beta particles. The fission process is complicated by the fact that different uranium-235 atoms split up in many different ways. For example, while one atom of 292U is splitting to give isotopes of rubidium (Z = 37) and cesium (Z = 55), another may break up to give isotopes of bromine (Z = 35) and lanthanum (Z = 57), while still another atom yields isotopes of zinc (Z = 30) and samarium (Z = 62) ... 

The stable neutron-to-proton ratio near the middle of the periodic table, where the fission products are located, is considerably smaller (—1-2) than that of uranium-235 (1.6). Hence the immediate products of the fission process contain too many neutrons for stability ... 

Reality Check Comparing the answers to (a) and (b), it appears that the fusion reaction produces about seven times as much energy per gram of reactant (57.2 X 107 versus 8.19 X 107 kj) as does the fission reaction. This factor varies from about 3 to 10, depending on the particular reactions chosen to represent the fusion and fission processes. 

The two nuclei on the right side are just two of the many possible products of the fission process. Since more than one neutron is released in each process, the fission reaction is a self-propagating, or chain reaction. Neutrons released by one fission event may induce other fissions. When fission reactions are run under controlled conditions in a nuclear reactor, the energy released by... 

The heart of the nuclear reactor boiler plant system is the reactor core, in which the nuclear fission process takes place. Nuclear fission is the splitting of a nucleus into two or more separate nuclei. Fission is usually by neutron particle bombardment and is accompanied by the release of a very large amount of energy, plus additional neutrons, other particles, and radioactive material. The generation of new neutrons during fission makes possible a chain reaction process and the subsequent... 

Once nuclear fission has been induced, it can continue, even if the supply of neutrons from outside is discontinued, provided that the fission produces more neutrons. Such self-sustaining fission takes place in uranium-235, which undergoes numerous fission processes, including... 

This reaction exemplifies the important process of methyl removal, which becomes even more significant in the case of multiply branched paraffins. The rather large exothermicity of Reaction 11 results from the fact that a secondary carbonium ion is formed. The beta fission process can be illustrated using reactions in 8-ra-hexylpentadecane (compound 2) as an example. Table II shows that the ions formed by C-C fission at a branch point (Ci4+, m/e = 197 and Ci5+, m/e = 211) have intensities appreciably larger than the other alkyl ions in the same region... 

THE NEW VISION INCLUDES VIABLE PROGRAMS FOR MANAGEMENT OF THE BY-PRODUCTS OF THE NUCLEAR FISSION PROCESS, INCLUDING RECYCLEOF ALL FISSIONABLE MATERIALS AND LONG-TERMISOLATION OF UNWANTED FISSION PRODUCTS FROM THE BIOSPHERE. 

Viable programs for management of the by-products of the nuclear fission process, including recycle of all fissionable materials and long-term isolation of unwanted fission products from the biosphere... 

With simple aliphatic amines, the initial diazonium cations (56) will break down extremely readily to yield carbocations (cf. p. 107) which are, for reasons that are not wholly clear, markedly more reactive than those obtained from other fission processes, e.g. RBr- R Bre. Where the prime purpose is the formation of carbocations, the nitrosation is better carried out on a derivative of the amine (to avoid formation of H20) under anhydrous conditions ... 

The reversible acid-catalyzed transacetalation of the cyclophane formal 3 has been shown to undergo a ring-fusion/ring-fission process to generate a mixture of polymer cyclic formaldehyde acetals by means of oxonium ion intermediates <06CEJ8566>. The stepwise... 

A chain reaction is a reaction that sustains itself once it has begun and may even expand. Normally, the limiting reactant is regenerated as a product to maintain the progress of the chain. Nuclear fission processes are considered chain reactions because the number of neutrons produced in the reaction equals or is greater than the number of neutrons absorbed by the fissioning nucleus. 

Therefore, the above fusion process produces about 10% more energy per amu of material than fission. However, the above fusion reaction is not a typical one because it involves the production of two particles from two particles of similar size. In general, fusion processes produce much more energy than fission processes on a per unit mass basis. 

Nuclear fission is the breakdown of a nucleus into two or more smaller nuclei with the release of energy. The most useful fission process involves the decay of U-235 when hit by a neutron ... 

Samarium is the 39th most abundant element in the Earths crust and the fifth in abundance (6.5 ppm) of all the rare-earths. In 1879 samarium was first identified in the mineral samarskite [(Y, Ce U, Fe) (Nb, Ta, Ti )Ojg]. Today, it is mostly produced by the ion-exchange process from monazite sand. Monazite sand contains almost all the rare-earths, 2.8% of which is samarium. It is also found in the minerals gadolmite, cerite, and samarskite in South Africa, South America, Australia, and the southeastern United States. It can be recovered as a byproduct of the fission process in nuclear reactors. 

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