Fission process, oxidizing nature

For the fission process, natural uranium foils and solid U02(N03)2.6H20 were used as targets. The isomer was separated with carrier from irradiated uranium foils in the following manner. The uranium was dissolved in concentrated hydrochloric acid which contained a little concentrated nitric acid. Iodide carrier was added and oxidized to periodate by means of sodium hypochlorite after the solution had been made basic with sodium carbonate. Then the usual redox steps were carried out reduction of 10 to I2 with NH2OH.HCI extraction of I2 into carbon tetrachloride back-extraction Into aqueous sodium bisulfite repetition of l2"I cycles until the y spectrum showed the presence only of iodine products or their xenon decay products. 

Oxidizing nature of the fission process. The fission of a mole of UF.1 would yield more equivalents of cation than of anion if the noble gas isotopes of half-life greater than 10 min were lost and if all other elements formed fluorides of their lowe.st reported valence state. If this were the case the system would, presumably, retain cation-anion equivalence by reduction of fluorides of the most noble fission products to metal and perhaps by reduction of some U + to U +. If, however, all the elements of uncertain valence state listed in Article 12-6.2 deposit as metals, the balance would be in the opposite direction. Only about 3.2 equivalents of coml)iiicd cations result, and since the number of active anion equivalents is a minimum of 4 (from the four fluorines of UF4), the deficiency must 1)0 alleviated by oxidation of the container. The evidence from the Aircraft Reactor Experiment, the in-pile loops, and the in-pile capsules has not shown the fission process to cause serious oxidation of the container it is possible that these experiments burned too little uranium to yield significant results. If fission of UF4 is shown to be oxidizing, the detrimental effect could be overcome by deliberate and occasional addition of a reducing agent to create a small and stable concentration of soluble UF3 in the fuel mixture. 

Uranium is the fourth metal in the actinide series. It looks much like other actinide metallic elements with a silvery luster. It is comparatively heavy, yet malleable and ductile. It reacts with air to form an oxide of uranium. It is one of the few naturally radioactive elements that is fissionable, meaning that as it absorbs more neutrons, it splits into a series of other lighter elements (lower atomic weights) through a process of alpha decay and beta emission that is known as the uranium decay series, as follows U-238—> Th-234—>Pa-234—>U-234—> Th-230 Ra-226 Rn-222 Po-218 Pb-2l4 At-218 Bi-2l4 Rn-218 Po-2l4 Ti-210—>Pb-210—>Bi-210 Ti-206—>Pb-206 (stable isotope of lead,... 

As enzymatic oxidative transformation of the PVA polymer can act as a multiple simultaneous event on the polymer with concurrent chain fission by the appropriate enzymes, the polymer can be broken down into small oligomers that can be channelled into the primary metabolism. This picture is not complete because PVA is usually more or less acetylated. The DH is a pivotal factor in almost every aspect of PVA application. Surprisingly there are very few data dealing with the enzymes involved in the deacetylation of not fuUy hydrolysed PVA polymer. In technical processes, esterase enzymes are widely applied to deal with PVAc structures. A good example is from the pulp and paper industry [85], where PVAc, a component of stickies , is hydrolysed to the less sticky PVA. Esterases from natural sources are known to accept the acetyl residues on the polymer as substrate but little detailed knowledge exists about the identity of acetyl esterases in the PVA degradative environment [86]. 

The dissolution time for the unreprocessed fuel would be at least 1 million years due to the limited water supply, even if a rapid oxidation of uranium to the hexavalent state and a subse-guent formation of water soluble carbonate complexes are assumed (15). Since the conditions are reducing in the groundwater (see beTow) the dissolution time would probably be several orders of magnitude larger. The unsignificant dissolution of uranium and fission products observed in the Oklo-deposit (16) is an example of a similar extremely slow leaching process in the natural environment. 

The extended radiation time for the domestic fuel increases the quantity of fission products and the higher actinides. Pure plutonium product poses nuclear weapons proliferation risk and is the primary reason reprocessing is not practiced in the United States. The modified PUREX process has been practiced on an industrial scale in Europe and supports the production of mixed uranium-plutonium fuel. Blended UO2 and PUO2 powder is compacted and sinter to form the mixed oxide (MOX) fuel pellets much like the enriched UO2 fuel. Natural and depleted uranium can be used to prepare MOX fuel and is the demonstrated option to recover fuel values from spent fuel. 

The uranium(IV) oxide, UO2, used as fuel in nuclear power plants has a higher percentage of the fissionable isotope uranium-235 than is present in the UO2 found in nature. To make fuel grade UO2, chemists first convert uranium oxides to uranium hexafluoride, UFg, whose concentration of uranium-235 can be increased by a process called gas diffusion. The enriched UFg is then converted back to UO2 in a series of reactions, beginning with... 

The synthesis of Catharine (250), " to which catharinine was initially believed to be closely related, has in fact been achieved by a process which involves the fission of ring D of the velbanamine component of leurosine (249). This conversion was first reported as a result of the accidental over-oxidation that occurred in the preparation of leurosine from anhydrovinblastine by means of t-butyl hydroperoxide in the presence of trifluoroacetic acid. The by-product in this reaction was initially regarded as the 21-lactam related to leurosine, but it has now been recognised as Catharine, and can be prepared equally well by oxidation in the absence of acid (Scheme 41) a radical mechanism appears to be involved. In view of this facile conversion under oxidising conditions, the status of Catharine as a bona fide natural product is open to question. Indeed, the status of leurosine itself as an alkaloid has been questioned, in view of the ease with which anhydrovinblastine is oxidised to leurosine, even in the absence of specific oxidising agents. For example, anhydrovinblastine is oxidised to leurosine if not stored in an inert atmosphere, and the conversion is even more rapid in solution, particularly in the presence of adsorbents such as silica or alumina. A conversion of 40% has been observed after only 72 hours at room temperature. In view of these results it is perhaps not surprising that anhydrovinblastine has not been isolated from any Catharanthus species examined to date. 

In accordance with the present invention, a novel process and apparatus for establishment of a self-sustaining neutron chain reaction of neutrons with a neutron fissionable isotope such as U, and 94 2 is provided. The invention is particularly advantageous since it may be applied to establishment of such a reaction in compositions such as natural uranium where the concentration of fissionable material is low. Thus, we have found that a self-sustaining reaction may be established by use of a suspension of natural uranium in a liquid moderator containing about 0.0025 to 0.04 atom of uranium per molecule of a moderator such as deuterium oxide or about 0.0013 to 0.02 atom of uranium per atom of deuterium. Where the liquid moderator is less efficient, and absorbs more neutrons than deuterium oxide, this range of uranium concentration is somewhat narrower. 

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