Nuclear reactor fuel

Results of uranium weight determination in nuclear reactor fuel elements. 

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... 

Uranium-235 Enrichment. The enrichment of uranium is expressed as the weight percent of in uranium. For natural uranium the enrichment level is 0.72%. Many appHcations of uranium requite enrichment levels above 0.72%, such as nuclear reactor fuel (56,57). Normally for lightwater nuclear reactors (LWR), the 0.72% natural abundance of is enriched to 2—5% (9,58). There are special cases such as materials-testing reactors, high flux isotope reactors, compact naval reactors, or nuclear weapons where enrichment of 96—97% is used. 

Carbide-based cermets have particles of carbides of tungsten, chromium, and titanium. Tungsten carbide in a cobalt matrix is used in machine parts requiring very high hardness such as wire-drawing dies, valves, etc. Chromium carbide in a cobalt matrix has high corrosion and abrasion resistance it also has a coefficient of thermal expansion close to that of steel, so is well-suited for use in valves. Titanium carbide in either a nickel or a cobalt matrix is often used in high-temperature applications such as turbine parts. Cermets are also used as nuclear reactor fuel elements and control rods. Fuel elements can be uranium oxide particles in stainless steel ceramic, whereas boron carbide in stainless steel is used for control rods. 

Large quantities of uranium oxide are required for nuclear reactor fuel. The uranium ore must be carefully purified and processed to desired shapes, causing high energy expenditure. 

Beryllium Oxide (Bromellite). BeO, mw 25.01, white amorph powd, mp 2530°, bp ca 3900°, d 3.01g/cc. Sol in coned acids and alkalies. V si sol in w. Prepn is by burning BeC03 at 900° in a Pt crucible to the oxide. It is used in nuclear reactor fuels and moderators as well as in powder metallurgy, ceramics, fuel cells and coatings (see above)... 

The maximum heat flux achievable with nucleate boiling is known as the critical heat flux. In a system where the surface temperature is not self-limiting, such as a nuclear reactor fuel element, operation above the critical flux will result in a rapid increase in the surface temperature, and in the extreme situation the surface will melt. This phenomenon is known as burn-out . The heating media used for process plant are normally self-limiting for example, with steam the surface temperature can never exceed the saturation temperature. Care must be taken in the design of electrically heated vaporisers to ensure that the critical flux can never be exceeded. 

ADU [Ammonium diuranate] A process for converting uranium hexafluoride into uranium dioxide, for use as a nuclear reactor fuel. The hexafluoride is hydrolyzed in water ... 

Nuclear reactor fuel, 25 851. See also Spent radioactive fuel... 

The following examples of terrorist events involving nuclear reactor fuel could produce large radiation doses (including emergency responders) resulting from the spread of contamination ... 

For the purpose of this discussion, radiological materials that could be used in a terrorist attack are divided into three categories (1) bomb-grade nuclear material, (2) nuclear reactor fuel and associated waste products, and (3) industrial sources. Bomb-grade nuclear material includes concentrated plutonium and/or highly enriched uranium (>20% U-235) that may be used to build a nuclear weapon, assuming a terrorist group cannot or has not already secured an assembled weapon. 

In 1942, the Mallinckrodt Chemical Company adapted a diethylether extraction process to purify tons of uranium for the U.S. Manhattan Project [2] later, after an explosion, the process was switched to less volatile extractants. For simultaneous large-scale recovery of the plutonium in the spent fuel elements from the production reactors at Hanford, United States, methyl isobutyl ketone (MIBK) was originally chosen as extractant/solvent in the so-called Redox solvent extraction process. In the British Windscale plant, now Sellafield, another extractant/solvent, dibutylcarbitol (DBC or Butex), was preferred for reprocessing spent nuclear reactor fuels. These early extractants have now been replaced by tributylphosphate [TBP], diluted in an aliphatic hydrocarbon or mixture of such hydrocarbons, following the discovery of Warf [9] in 1945 that TBP separates tetravalent cerium from... 

Wymer, R. G. Vondra, B. L. Eds. Light Water Nuclear Reactor Fuel Cycle CRC Press Boca Raton, Florida, 1981. 

Uses. Fluorinating agent incendiary igniter and propellant for rockets in nuclear reactor fuel processing pyrolysis inhibitor for fluorocarbon polymers... 

Chlorine trifluoride is used in rocket propellant incendiaries and in processing of nuclear reactor fuel. It also is used as a fluorinating agent and as an inhibitor of fluorocarbon polymer pyrolysis. 

Dysprosium is used in nuclear reactor fuels to measure neutron flux. It also is used as a fluorescence activator in phosphors. 

Nuclear reactor coolant Nuclear reactor fuel Nuclear reactors... 

Industrial utilization of neptunium has been very limited. The isotope 1 Np has been used as a component in neutron detection instruments. Neptunium is present in significant quantities in spent nuclear reactor fuel and poses a threat to the environment. A group of scientists at the U.S. Geological Survey (Denver, Colorado) has studied the chemical speciation of neptunium (and americium) in ground waters associated with rock types that have been proposed as possible hosts for nuclear waste repositories. See Cleveland reference. 

Principal applications for radiography include the inspection of castings, electrical assemblies, weldments, small, thin, and complex wrought products, some nonmetallics. solid propellant rocket motors, cans or containers, composites, and nuclear reactor fuel rods, amoug many others. 

Processes for the isolation and purification of plutonium, including the enrichment of spent nuclear reactor fuels, arc described in the entry on Nuclear Power Technology. These processes take advantage of Pu s several oxidation states, each of which has different chemical properties. The processes may involve carrier precipitation, solvent extraction, and ion exchange. 

For a 1000-MWe nuclear reactor fueled with a fuel containing 5% 235U, calculate the uranium use in a year of full-time operation. 

Fuel reprocessing has three objectives (a) to recover U or Pu from the spent fuel for reuse as a nuclear reactor fuel or to render the waste less hazardous, (b) to remove fission products from the actinides to lessen short-term radioactivity problems and in the case of recycle of the actinides, to remove reactor poisons, and (c) to convert the radioactive waste into a safe form for storage. Fuel reprocessing was/is important in the production of plutonium for weapons use. 

D. R. Odander, Fundamental Aspects of Nuclear Reactor Fuel Elements, National Technical Information Service, Springfield, Va., 1976, Chapt. 17. 

Americium and curium isotopes formed during irradiation of nuclear reactor fuels are diverted into the high-level waste (HLW) stream during fuel reprocessing. The HLW is thus the biggest... 

Although the fission products could be recovered as byproducts from the waste from spent nuclear reactor fuel, special-purpose neutron irradiation of highly enriched uranium (isotopically separated uranium-235) followed by chemical separation is the normal production method. The major products, molybdenum-99 and iodine-131 with fission yields of 6.1 and 6.7 percent, respectively, have important medical applications. Mo-99,... 

Eister, W., Stoughton, R. Sullivan, W., Processing of Nuclear Reactor Fuel, Principles of Nuclear Reactor Engineering, Glasstone, S., (Ed.), Van Nostrand, New York, 1955. 

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