REPROCESSING

Mastery of the handling of spent nuclear fuel, including safe disposal of the radioactive waste, is a prerequisite for the use of nuclear energy. 

An example of the effect of poisoning is the series of isobars with mass number A = 135  

The neutron absorption of Xe is extremely high. The ratio of the number of atoms transmuting by jS decay to the number transformed by (n, y) reactions depends on the neutron flux density 0  

The fission products that are mainly responsible for neutron absorption are listed in Table 11.9. With respect to the mass the lanthanides represent the greatest fraction, but with regard to neutron absorption the noble gases are most important due to the high value of for Xe (2.65 10 b). 

The effect of poisoning can be compensated to a certain extent by an excess reactivity or by installation of a breeder blanket (an outer layer of Th) in which new fissile material is produced. In fast reactors the effect of poisoning is less important. 

When recycling acrylic based compounds (Acry-lite , Cyrolite and XT) 100% regrind can be used without an effect on properties if properly dried and free of contamination. However, if regrind contains hnes these may adhere to the screw and eventually cause discoloration. 

For PET/elastomer blends (Rynite ), some loss of properties results from the addition of regrind. About 10% loss for 25% regrind, and 15% for 50% regrind was reported. 

Blends of POM/TPU Ultraform ) must be reprocessed with care. When the processing stock contains regrind of different pellet size, the change in the flow properties may affect the product characteristics. Furthermore, since these blends are immiscible with other thermoplastics, contaminated regrind may lead to delamination. Contamination with other thermoplastics, especially with small amount of PVC, may cause sudden, uncontrollable decomposition engendered by dehydrochlorination of PVC. 

Over the years, developments in the area of polymer blends have primarily aimed at improving final properties, particularly impact resistance. To obtain the maximum impact strength, the morphology should be of the matrix/dispersed phase type, and the dispersed phase must be in the 

Other typically observed morphologies are co-continuity of phases and dispersion of lamellar domains. Co-continuity might allow to draw on properties of both constituents, yielding for example a stiffness/ductility balance not achievable with pure polymers. Lamellar morphologies will obviously yield improved barrier performance when the proper constituents are selected. 

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Oil recycling Oil Recycling Act Oil Red [85-83-6] Oil refineries Oil reprocessing Oil re-refimng Oil resistance... 

Reprocessing Reproductive physiology Reproductive system Reprographic inks Reprography Re-refining... 

If the spent fuel is processed in a nuclear fuel reprocessing plant, the radioactive iodine species (elemental iodine and methyl iodide) trapped in the spent fuel elements ate ultimately released into dissolver off gases. The radioactive iodine may then be captured by chemisorption on molecular sieve 2eohtes containing silver (89). 

Nuclear Fuel Reprocessing. Spent fuel from a nuclear reactor contains Pu, Th, and many other radioactive isotopes (fission... 

Special safety constraints apply to equipment selection, design, and operation in nuclear reprocessing (269). Equipment should be reHable and capable of remote control and operation for long periods with minimal maintenance. Pulsed columns and remotely operated mixer—settlers are commonly used (270). The control of criticaHty and extensive monitoring of contamination levels must be included in the process design. 

Uranium Extraction from Ore Leach Liquors. Liquid—Hquid extraction is used as an alternative or as a sequel to ion exchange in the selective removal of uranium [7440-61-1] from ore leach Hquors (7,265,271). These Hquors differ from reprocessing feeds in that they are relatively dilute in uranium and only slightly radioactive, and contain sulfuric acid rather than nitric acid. 

J. T. Long, Pngineeringfor Nuclear Fuel Reprocessing, Gordon and Breach, Inc., New York, 1967. 

Disposal of spent hydrogenation catalyst requires a special chemical waste landfill because of its nickel content and the fact that oil-soaked catalysts tend to be pyrophoric. Compared to disposal costs, reprocessing to recover the nickel may become economically viable. 

In France, Compagnie Europnene du Zirconium (CEZUS) now owned jointly by Pechiney, Eramatome, and Cogema, uses a separation (14) based on the extractive distillation of zirconium—hafnium tetrachlorides in a molten potassium chloride—aluminum trichloride solvent at atmospheric pressure at 350°C. Eor feed, the impure zirconium—hafnium tetrachlorides from the zircon chlorination are first purified by sublimation. The purified tetrachlorides are again sublimed to vapor feed the distillation column containing the solvent salt. Hafnium tetrachloride is recovered in an enriched overhead fraction which is accumulated and reprocessed to pure hafnium tetrachloride. 

Hafnium neutron absorption capabilities have caused its alloys to be proposed as separator sheets to allow closer spacing of spent nuclear fuel rods in interim holding ponds. Hafnium is the preferred material of constmction for certain critical mass situations in spent fuel reprocessing plants where hafnium s excellent corrosion resistance to nitric acid is also important. 

Synthetic fluids are safe, noncorrosive, essentially nontoxic, and thermally stable when operated under conditions recommended by the manufacturers. Generally, these fluids are more expensive than petroleum oils, but the synthetics can usually be reprocessed to remove degradation products. There are several classes of chemicals offered permitting a wide temperature range of appHcation. Any heat-transfer fluid in use should be examined periodically to monitor degradation or contamination. 

The manufacturers of synthetic fluids offer technical service and consultation, and fluid reprocessing service can be arranged between the suppHer and the user. Complete physical properties and detailed information concerning synthetic fluids are reported in the manufacturers product Hterature (13—36). The physical characteristics of the synthetic fluids can be found in Table 1. 

Argon-40 [7440-37-1] is created by the decay of potassium-40. The various isotopes of radon, all having short half-Hves, are formed by the radioactive decay of radium, actinium, and thorium. Krypton and xenon are products of uranium and plutonium fission, and appreciable quantities of both are evolved during the reprocessing of spent fuel elements from nuclear reactors (qv) (see Radioactive tracers). 

Separation of krypton and xenon from spent fuel rods should afford a source of xenon, technical usage of which is continuously growing (84). As of this writing, however, reprocessing of spent fuel rods is a pohtical problem (see Nuclearreactors). Xenon from fission has a larger fraction of the heavier isotopes than xenon from the atmosphere and this may affect its usefulness in some appHcations. 

Neutron-rich lanthanide isotopes occur in the fission of uranium or plutonium and ate separated during the reprocessing of nuclear fuel wastes (see Nuclearreactors). Lanthanide isotopes can be produced by neutron bombardment, by radioactive decay of neighboring atoms, and by nuclear reactions in accelerators where the rate earths ate bombarded with charged particles. The rare-earth content of solid samples can be determined by neutron... 

Lead bricks are generahy used as temporary shields for radiation sources at nuclear power stations, research institutes, hospitals, and fuel reprocessing plants. Plat, rectangular bricks requite a double layer with staggered seams whereas the interlocking bricks requite only one course. Lead shot can be poured into inaccessible areas like a Hquid. 

In addition, solvent extraction is appHed to the processing of other metals for the nuclear industry and to the reprocessing of spent fuels (see Nuclearreactors). It is commercially used for the cobalt—nickel separation prior to electrowinning in chloride electrolyte. Both extraction columns and mixer-settlers are in use. 

Uranium-239 [13982-01 -9] has a half-life of 23.5 min neptunium-239 [13968-59-7] has a half-life of 2.355 d. Recycling or reprocessing of spent fuel involves separation of plutonium from uranium and from bulk fission product isotopes (see Nuclearreactors, chemical reprocessing). 

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