235U

Kilogram amounts of neptunium ( Np) have been isolated as a by-product of the large-scale synthesis of plutonium in nuclear reactors that utilise 235u and 238u as fuel. The following transmutations occur ... 

The raw material for nuclear reactor fuel, uranium, exits the mining—milling sequence as uranium oxide. Because of its color, it is called yellow cake. The yellow cake is converted to uranium hexafluoride and enriched in 235u... 

The GANDU Reactors. The Canadian deuterium uranium (CANDU) reactors are unique among power reactors in several respects. Heavy water is used as moderator natural uranium having 235u... 

Homogeneous Aqueous Reactors. As a part of the research on neutron multiphcation at Los Alamos in the 1940s, a small low power reactor was built using a solution of uranium salt. Uranyl nitrate [36478-76-9] U02(N0 2> dissolved in ordinary water, resulted in a homogeneous reactor, having uniformly distributed fuel. This water boiler reactor was spherical. The 235u... 

The determination of critical si2e or mass of nuclear fuel is important for safety reasons. In the design of the atom bombs at Los Alamos, it was cmcial to know the critical mass, ie, that amount of highly enriched uranium or plutonium that would permit a chain reaction. A variety of assembhes were constmcted. Eor example, a bare metal sphere was found to have a critical mass of approximately 50 kg, whereas a natural uranium reflected 235u sphere had a critical mass of only 16 kg. 

One of the early popular low power research and training reactors was the AGN-201, suppHed by Aerojet General Nuclear. This is a homogeneous sohd fuel reactor, consisting of a mixture of polyethylene and uranium at 20% enrichment in The core 235U... 

In early 1941, 0.5 )-lg of Pu was produced (eqs. 3 and 4) and subjected to neutron bombardment (9) demonstrating that plutonium undergoes thermal neutron-induced fission with a cross section greater than that of U. In 1942, a self-sustaining chain reaction was induced by fissioning 235u... 

Cost and Value of Plutonium. The cost of building all U.S. nuclear weapons has been estimated as 378 biUion in 1995 dollars (24). If half of this sum is attributed to U.S. weapons-grade plutonium production (- lOOt), the cost is 1.9 x 10 /kg of weapons-grade Pu. Some nuclear weapons materials (Be, enriched U, Pu) also have value as a clandestine or terrorist commodity. The economic value of reactor-grade plutonium as a fuel for electric power-producing reactors has depended in the past on the economic value of pure 235u... 

The Oklo Phenomenon. Naturally occurring uranium consists mainly of and fissionable The isotopic ratio can be calculated from the relative decay rates of the two isotopes. Because decays faster than the isotopic ratio decreases with time. In 1997, the isotopic abundance of 235u... 

Standard S1 (233u) 234y 235u (236u) 238u... 

Figure 14. (a) Plot of U-Pa versus U-Th disequilibria for arc lavas. The Tonga samples are those (23ipa/235u) (230xh/ 38 j < 1 as expected from U addition by subduction zone fluids. However, all... 

A nuclear power plant that generates 1000 MW of power uses 3.2 kg per day of 235U. Naturally occurring uranium contains 0.7% 235U and 99.7% 238U. What mass of natural uranium is required to keep the generator running for a day ... 

Depleted uranium (DU)—Uranium having a percentage of 235U smaller than the 0.7% found in natural uranium. It is obtained as a by-product from 235U enrichment. 

Enriched Uranium—Uranium in which the abundance of the 235U isotope is increased above normal. 

Enrichment, Isotopic—An isotopic separation process by which the relative abundances of the isotopes of a given element are altered, thus producing a form of the element that has been enriched in one or more isotopes and depleted in others. In uranium enrichment, the percentage of uranium-235 in natural uranium can be increased from 0.7% to >90% in a gaseous diffusion process based on the different thermal velocities of the constituents of natural uranium (234U, 235U, 238U) in the molecular form UF6. 

Soft, silver white metal that is isolated in the tiniest of amounts. All isotopes are radioactive, the longest-lived has a half-life of 22 years. The element is an intermediate in the decay series of 235U. Strong alpha emitter that is used in radioactivation analysis and forms an effective neutron source with beryllium. 

Strongly radioactive, short-lived element that can be found in tiny amounts in uranium ores. It arises fleetingly from 235U in its decay chain through actinium (227Ac). Is only of scientific value as it has a maximum half-life of about 22 minutes. Nevertheless, in its short existence it is the atom with the largest diameter (0.270 nm cesium 0.265 nm). 

Radioactive, silvery metal of which only about 125 g exists worldwide, isolated from reactor material. Protactinium occurs in the decay series of 238U (K. Fajans) as 234Pa. It also occurs in that of 235U this isotope, 231Pa, was discovered by L. Meitner and 0. Hahn. The element is only of scientific interest. 

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