Uranium heat source

The reactor is a helium/xenon (Me/Xe) gas-cooled, fast neutron spectrum, fission reactor with an approximately 1 MWt uranium heat source directly coupled to a gas Brayton energy conversion equipment The reactor requires a radiation shield to provide a shadow volume of diminished radiation to the rest of the Spaceship. The radiation shield concept is an elliptical cone which produces this shadow with half-angles of 12" and 6°, All major elements of the spacecraift and Mission Modules will be located within this shielded area... 

Steam turbines are an even older technology, providing power for over 100 years. Most utility power is produced by steam turbines. The steam turbine generator depends on a separate heat source for steam, often some type of boiler, which may run on a variety of fuels, such as coal, natural gas, petroleum, uranium, wood and waste products including wood chips or agricultural by-products. 

At Los Alamos National Laboratory in New Mexico the Analytical Chemistry Group (C-AAC) supports the Pu-238 Heat Source Project that fabricates heat sources for use in the space industry. These heat sources have been used on NASA s deep-space probes and on instruments exploring the surface of Mars. The chemical and isotopic purity of the heat sources are critically controlled to ensure dependable service. The Radiochemistry Task Area performs analyses of the heat source material for four radioisotopes americium-241, plutonium-238, neptunium-237, and uranium-235. 

A. Uranium-235 and plutonium-239 are the two fissile isotopes used for nuclear power. 238U is the most common uranium isotope. 238Pu is used as a heat source for energy in space probes and some pacemakers. 

For the fluorometric method, uranium is concentrated by co-precipitation with aluminum phosphate, dissolved in diluted nitric acid containing magnesium nitrate as a salting agent, and the co-precipitated uranium is extracted into ethyl acetate and dried. The uranium is dissolved in nitric acid, sodium fluoride flux is added, and the samples fused over a heat source (EPA 1980). 

More controversial (although sometimes cited as proven fact) have been claims (e.g., Taylor and Jakes, 1974 Taylor, 1982) that the bulk Moon is enriched roughly twofold in the cosmochemically refractory lithophile elements (a class that includes the REEs, the heat sources thorium and uranium, and the major elements aluminum, calcium, and titanium), and that compared to Earth s primitive mantle, the Moon s silicate mg ratio is much lower, i.e., its EeO concentration is much higher. Neither of these claims has been confirmed by recent lunar science developments, which include the advent of global thorium and samarium maps (Lawrence et al., 2002a Prettyman et al., 2002), data from lunar meteorites, and some radically changed interpretations of the Apollo seismic database. 

The primary use for plutonium (Pu) is in nuclear power reactors, nuclear weapons, and radioisotopic thermoelectric generators (RTGs). Pu is formed as a by-product in nuclear reactors when uranium nuclei absorb neutrons. Most of this Pu is burned (fissioned) in place, but a significant fraction remains in the spent nuclear fuel. The primary plutonium isotope formed in reactors is the fissile Pu-239, which has a half-life of 24 400 years. In some nuclear programs (in Europe and Japan), Pu is recovered and blended with uranium (U) for reuse as a nuclear fuel. Since Pu and U are in oxide form, this blend is called mixed oxide or MOX fuel. Plutonium used in nuclear weapons ( weapons-grade ) is metallic in form and made up primarily (>92%) of fissile Pu-239. The alpha decay of Pu-238 (half-life = 86 years) provides a heat source in RTGs, which are long-lived batteries used in some spacecraft, cardiac pacemakers, and other applications. 

The iron would not be molten and flow, however, without a continuous heat source to keep it from solidifying. Radioactive fission energy from uranium and thorium decay has long been the assumed source of the heat in the core, and still provides that heat, but not enough to have sustained a magnetic field for 4 billion years. 

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. 

The isotope Cm is the largest contributor to the alpha activity of irradiated uranium fuel from power reactors. It is an important source of the 2n + 2 decay chain in the high4evel wastes from fuel reprocessing. The alpha activity of Cm results in an internal heat-generation rate of 120 W/g of pure Cm. Separated Cm, prepared by the neutron irradiation of Am, provides a useful alternative for a thermoelectric source and for radionuclide batteries when relatively high outputs are desired over short periods of the order of its half-Ufe of 163 days. For example, a space power generator denoted as SNAP-11 contained 7.5 g of Cm and produced 20 W of thermoelectric power. Cm is also the decay source of Pu, which is used as a longer-lived radioisotope heat source. 

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