Uranium enriched

By far the largest use of hydrogen fluoride is in the manufacture of fluorocarbons which find a wide variety of uses including refrigerants, aerosol propellants and anaesthetics. Hydrogen fluoride is also used in the manufacture of synthetic cryolite, Na3AIFg, and the production of enriched uranium. 

Supply Projections. Additional supphes are expected to be necessary to meet the projected production shortfall. A significant contribution is likely to come from uranium production centers such as Eastern Europe and Asia, which are not included in the capabihty projections (27). The remaining shortfall between fresh production and reactor requirements is expected to be filled by several alternative sources, including excess inventory drawdown. These shortfalls could also be met by the utili2ation of low cost resources that could become available as a result of technical developments or pohcy changes, production from either low or higher cost resources not identified in production capabihty projections, recycled material such as spent fuel, and low enriched uranium converted from the high enriched uranium (HEU) found in warheads (28). 

HEU De-Enrichment. Highly enriched uranium (HEU), initially enriched to >93% U, for use in research, naval reactors, and nuclear weapons, may be de-enriched and fabricated into fuel for civihan nuclear reactors. An estimate of the world inventory of highly enriched uranium in the nuclear weapons states is provided in Table 6 (34). 

An agreement between the United States and Russia led to a commitment in 1994 by the United States to buy 500 metric tons of Russian HEU, which has been converted to low enriched uranium (LEU). The HEU must come from dismanded nuclear weapons before it is converted to LEU. The sale of converted HEU to the United States is to be carried out on a timetable in which no less than 10 t are to be converted in each of the first five years of the agreement and no less than 30 t in each year thereafter (35). In all, the agreement would last for 20 years if only these minimums were sold each year. 

De-enrichment of HEU from approximately 93% to 3% can be accompHshed using the depleted tails from the original enrichment process. These tails contain on the average 0.20% U. The de-enrichment of 11 of HEU uses 32 t of tads, yielding approximately 33 t of fuel having an enrichment of 3% U. Producing the same amount of 3% enriched uranium from natural sources would requite approximately 180 t of natural uranium metal. Therefore, 1 t of HEU is equivalent to 180 t of natural uranium. 

The recycle weapons fuel cycle rehes on the reservoir of SWUs and yellow cake equivalents represented by the fissile materials in decommissioned nuclear weapons. This variation impacts the prereactor portion of the fuel cycle. The post-reactor portion can be either classical or throwaway. Because the avadabihty of weapons-grade fissile material for use as an energy source is a relatively recent phenomenon, it has not been fully implemented. As of early 1995 the United States had purchased highly enriched uranium from Russia, and France had initiated a modification and expansion of the breeder program to use plutonium as the primary fuel (3). AH U.S. reactor manufacturers were working on designs to use weapons-grade plutonium as fuel. 

The Hanford N Reactor. The Hanford N reactor was built in 1964 for purposes of plutonium production during the Cold War. It used graphite as moderator, pierced by over 1000 Zircaloy 2 tubes. These pressure tubes contained slightly enriched uranium fuel cooled by high temperature light water. The reactor also provided 800 MWe to the Washington PubHc Power Supply System. This reactor was shut down in 1992 because of age and concern for safety. The similarity to the Chemobyl-type reactors played a role in the decision. 

Another reactor that was approved for development was a land-based prototype submarine propulsion reactor. Westinghouse Electric Corp. designed this pressurized water reactor, using data collected by Argonne. Built at NRTS, the reactor used enriched uranium, the metal fuel in the form of plates. A similar reactor was installed in the submarine l autilus. 

A series of tests were performed at the AFC s National Reactor Testing Station in Idaho, starting in 1953. The reactor was situated outdoors, and was operated remotely. The core of the first version had fuel assembhes of aluminum and enriched uranium plates of the Materials Testing Reactor (MTR) type, installed in a water tank. One of the five control rods could be ejected downward and out of the core by spring action upon intermption of a magnet... 

Over the years, a variety of fuel types were employed. Originally, natural uranium slugs canned in aluminum were the source of plutonium, while lithium—aluminum alloy target rods provided control and a source of tritium. Later, to permit increased production of tritium, reactivity was recovered by the use of enriched uranium fuel, ranging from 5—93%. 

As a part of the power demonstration program of the AFC in the 1950s, the Enrico Fermi fast breeder reactor (Fermi-1) was built near Detroit by a consortium of companies led by Detroit Edison. Fermi-1 used enriched uranium as fuel and sodium as coolant, and produced 61 MWe. It suffered a partial fuel melting accident in 1966 as the result of a blockage of core coolant flow by a metal plate. The reactor was repaired but shut down permanently in November 1972 because of lack of binding. Valuable experience was gained from its operation, however (58). 

The first reactor, SM-1, was operated at Fort Belvoir, Virginia. Others were located ia Wyoming, Greenland, Alaska, and Antarctica. The fuel consisted of highly enriched uranium as the dioxide, dispersed ia stainless steel as plates or rods. Details are available ia Reference 18. 

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. 

A number of pool, also called swimming pool, reactors have been built at educational institutions and research laboratories. The core in these reactors is located at the bottom of a large pool of water, 6 m deep, suspended from a bridge. The water serves as moderator, coolant, and shield. An example is the Lord nuclear reactor at the University of Michigan, started in 1957. The core is composed of fuel elements, each having 18 aluminum-clad plates of 20% enriched uranium. It operates at 2 MW, giving a thermal flux of 3 x 10 (cm -s). The reactor operates almost continuously, using a variety of beam tubes, for research purposes. 

The technologically most important isotope, Pu, has been produced in large quantities since 1944 from natural or partially enriched uranium in production reactors. This isotope is characterized by a high fission reaction cross section and is useful for fission weapons, as trigger for thermonuclear weapons, and as fuel for breeder reactors. A large future source of plutonium may be from fast-neutron breeder reactors. 

The NRC also imposes special security requirements for spent fuel shipments and transport of highly enriched uranium or plutonium materials that can be used in the manufacture of nuclear weapons. These security measures include route evaluation, escort personnel and vehicles, communications capabiHties, and emergency plans. State governments are notified in advance of any planned shipment within their state of spent fuel, or any other radioactive materials requiring shipment in accident-proof. Type B containers. 

Production in Fission of Heavy Elements. Tritium is produced as a minor product of nuclear fission (47). The yield of tritium is one to two atoms in 10,000 fissions of natural uranium, enriched uranium, or a mixture of transuranium nucHdes (see Actinides and transactinides Uranium). 

In 1985, owiag to the declining demand by the nuclear power industry for enriched uranium, the Oak Ridge gaseous diffusion plant was taken out of operation and, subsequently, was shut down. The U.S. gaseous diffusion plants at Portsmouth, Ohio and Paducah, Kentucky remain ia operation and have a separative capacity of 19.6 million SWU (separative work unit) per year which as of this writing is not fully utilized. 

The large physical size of the later Magnox stations, such as Wylfa, led to the development of the more compact advanced gas-cooled reactor (AGR) design [31] that could utilize the standard turbine generator units available in the UK, Stainless-steel clad, enriched uranium oxide fuel can tolerate higher temperatures... 

The Canadian Deuterium Uranium reactor fissions with natural uranium, hence, no dependence on national or international fuel enrichment facilities that are needed to enrich uranium to about 3% U-235 to achieve criticality with light water moderation. 

Finally, the enriched uranium of converted back into UO,. The UO, is pressed into small fuel pellets and packaged in a metal tube (made of a zirconium alloy) for use in a nuclear reactor. 

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