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Because natural uranium consists mainly of the mass isotope U and only about 0. The process began with natural uranium and resulted in enriched uranium and depleted uranium. The first U. Additional enrichment plants were later built in Piketon, Ohio, and Paducah, Kentucky. Highly enriched uranium HEU contains 20 weight percent or more of U; it was fashioned into weapon components and also used as reactor fuel. Low enriched uranium LEU , which contains less than 20 weight percent of U, and natural uranium were used as reactor fuel for plutonium production.
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Depleted uranium was used in weapon components and for Pu production. However, as early as , LEU was used for reactor fuel. Uranium enrichment has resulted in the accumulation of about , metric tons of depleted uranium hexafluoride DUF 6 , most of which was stored in large carbon steel cylinders at the enrichment facilities. Research opportunities that might lead to improved options for management, reuse, or disposal of this material are discussed in Chapter 6.
Fuel and target fabrication consisted of the foundry and machine shop operations required to convert uranium feed material, principally metal, into fuel and target elements. Some later production reactors used separate fuel and target elements, while early production reactors used the same elements for both fuel and targets. Uranium ingots were extruded, rolled, drawn, swaged, straightened, and outgassed to produce rods and plates.
The rods were machined, ground, cleaned, coated, clad, and assembled into finished fuel. Reactor fuel and target fabrication was initially carried out by private contractors and at the Hanford, Washington, and the Savannah River, South Carolina, production reactor sites.
At SRS, fuel rods were made by extrusion of an alloy of aluminum and HEU to form thin-walled, aluminum-clad fuel tubes. Reactor operations include loading and removal of fuel and target elements, reactor maintenance, and the operation of the reactor itself. Nine full-scale production reactors were located at Hanford, and five others were built at the SRS.
Reactor operations created essentially all the nuclear materials used in the DOE complex. Except for a few special cases, such as research reactor fuel, the highly radioactive spent fuel and targets were reprocessed to recover plutonium, uranium, and other isotopes and to separate waste materials. However, when the United States stopped its plutonium production in , some spent fuels, including targets, were left unreprocessed. Chemical separation involved dissolving SNF and targets and isolating and concentrating the plutonium, uranium, and other nuclear materials they contained.
Three basic chemical separation processes were used on a production scale in the United States: bismuth phosphate, reduction oxidation, and plutonium uranium extraction PUREX. Chemical separation of spent fuel and target elements produced large volumes of highly radioactive waste high-level waste , and large quantities of low-level radioactive wastewater, solid low-level waste, and mixed low-level waste. Separated nuclear materials from reprocessing that are dealt with in this report include plutonium Chapter 3 , cesium and strontium Chapter 5 , and special isotopes Chapter 7.
Weapons operations include the assembly, maintenance, and dismantlement of nuclear weapons. Weapons operations were chiefly. Assembly is the process of joining together separately manufactured components and major parts into complete, functional, and certified nuclear warheads for delivery to the Department of Defense. Maintenance includes the modification and upkeep of a nuclear weapon during its life cycle.
Dismantlement involves the reduction of retired warheads to a nonfunctional state and the disposition of their component parts. The dismantlement process yields parts containing special nuclear materials, high explosives, hazardous materials, and other components with hazardous and nonhazardous properties.
Some parts are returned to the facility where they were originally produced. Other parts are maintained in storage e. With respect to the excess plutonium, a major step toward disposition will be conversion to mixed oxide fuel for commercial power reactors at a new facility to be built at SRS see Chapter 3. The two canyons were similar when first constructed but were modified over the years to provide separate capabilities, though many operations can be done in either, but at different rates. Originally, both utilized the PUREX solvent extraction process to separate plutonium from irradiated natural uranium.
The original B-Lines were based on the plutonium peroxide, plutonium tetrafluoride, calcium reduction route to metal. The installation also incorporated recovery facilities for slag and crucible, out of specification material, and other residues, because an original goal was that no backlog of recoverable plutonium was to be accumulated.
From to , F-Canyon was shut down for the installation of higher-capacity equipment for solvent extraction and a new plutonium finishing line based on a plutonium fluoride precipitation route to metal. Later, more recovery capacity was added.
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Meanwhile, H-Canyon continued in plutonium production. During this period, reactor operation changed to driver elements of HEU and targets of DU metal for plutonium production and of lithium-aluminum alloy for tritium production. Operation of F-Canyon restarted in , and H-Canyon was shut down and modified to maintain nuclear safety while processing HEU driver elements.
Changes included dissolver inserts to provide safe geometry, lowered concentration of the tributylphosphate extractant, and instruments to monitor and control concentrations of the uranium in the liquid phases.
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Only a few months were required for production in H-Canyon to resume. A number of functions and capabilities were added to the separations facilities for special programs. Recovery of Np, fabrication of reactor targets, and separation and recovery of neptunium and. Pu from the targets were provided by canyon installations and finishing facilities in H-Canyon. Special dissolver inserts allowed wide varieties of fuels to be processed, including enriched fuels being returned from domestic and foreign research reactors.