Reactor power

The introscopic image of power reactor fuel assembly reveals the presence the fuel elements, the tomographic image reveals their filling by fuel and location. 

The uses of nuclear fuels to generate electrical power, to make isotopes for peaceful purposes, and to make explosives are well known. The estimated world-wide capacity of the 429 nuclear power reactors in operation in January 1990 amounted to about 311,000 megawatts. 

Its importance depends on the nuclear property of being readily fissionable with neutrons and its availability in quantity. The world s nuclear-power reactors are now producing about 20,000 kg of plutonium/yr. By 1982 it was estimated that about 300,000 kg had accumulated. The various nuclear applications of plutonium are well known. 238Pu has been used in the Apollo lunar missions to power seismic and other equipment on the lunar surface. As with neptunium and uranium, plutonium metal can be prepared by reduction of the trifluoride with alkaline-earth metals. 

One of the most significant sources of change in isotope ratios is caused by the small mass differences between isotopes and their effects on the physical properties of elements and compounds. For example, ordinary water (mostly Ej O) has a lower density, lower boiling point, and higher vapor pressure than does heavy water (mostly H2 0). Other major changes can occur through exchange processes. Such physical and kinetic differences lead to natural local fractionation of isotopes. Artificial fractionation (enrichment or depletion) of uranium isotopes is the basis for construction of atomic bombs, nuclear power reactors, and depleted uranium weapons. 

Nuclear Applications. Powder metallurgy is used in the fabrication of fuel elements as well as control, shielding, moderator, and other components of nuclear-power reactors (63) (see Nuclearreactors). The materials for fuel, moderator, and control parts of a reactor are thermodynamically unstable if heated to melting temperatures. These same materials are stable under P/M process conditions. It is possible, for example, to incorporate uranium or ceramic compounds in a metallic matrix, or to produce parts that are similar in the size and shape desired without effecting drastic changes in either the stmcture or surface conditions. OnlyHttle post-sintering treatment is necessary. 

Safety. A large inventory of radioactive fission products is present in any reactor fuel where the reactor has been operated for times on the order of months. In steady state, radioactive decay heat amounts to about 5% of fission heat, and continues after a reactor is shut down. If cooling is not provided, decay heat can melt fuel rods, causing release of the contents. Protection against a loss-of-coolant accident (LOCA), eg, a primary coolant pipe break, is required. Power reactors have an emergency core cooling system (ECCS) that comes into play upon initiation of a LOCA. 

P. Cohen, Water Coolant Technology for Power Reactors, American Nuclear Society, La Grange Park, lU., 1980. 

Lightwater reactors, the primary type of nuclear power reactor operated throughout the world, are fueled with uranium dioxide [1344-57-6] UO2 miched from the naturally occurring concentration of 0.71% uranium-235 [15117-96-17, to approximately 3% (1). As of this writing all civiUan nuclear... 

Demand. The demand for uranium in the commercial sector is primarily determined by the requirements of power reactors. At the beginning of 1993, there were 424 nuclear power plants operating worldwide, having a combined capabity of about 330 GWe. Moderate but steady growth is projected for nuclear capacity to the year 2010. The capacity in 2010 is expected to be about 446 GWe (29). 

W. S. Groenier, Equipmentfor the Dissolution of Core Materialfrom S beared Power Reactor Fuels, ORNL/TM-3194, Oak Ridge National Laboratory, Oak... 

The chronology of the development of nuclear reactors can be divided into several principal periods pre-1939, before fission was discovered (12) 1939—1945, the time of World War II (13—15) 1945—1963, the era of research, development, and demonstration (16—18) 1963—mid-1990s, during which reactors have been deployed in large numbers throughout the world (10,18) and extending into the twenty-first century, a time when advanced power reactors are expected to be built (19—23). Design of nuclear reactors has been based on a combination of theory, measurement of basic and derived parameters, and experiments with complete systems (24—27). 

The GANDU Reactors. The Canadian deuterium uranium (CANDU) reactors are unique among power reactors in several respects. Heavy water is used as moderator natural uranium having 235u... 

The United States continued fast-breeder reactor research and development with the building of the fast flux test faciHty (FFTF) at Hanford and the SEFOR reactor in Arkansas (59). The next plaimed step was to build a prototype power reactor, the Clinch River fast-breeder plant (CRFBP), which was to be located near Oak Ridge, Teimessee. 

Fig. 11. Reactor core of MONJU, the Japanese fast-breeder reactor. Courtesy of Power Reactor and Nuclear Fuel Development Corp.

Homogeneous Aqueous Reactors. As a part of the research on neutron multiphcation at Los Alamos in the 1940s, a small low power reactor was built using a solution of uranium salt. Uranyl nitrate [36478-76-9] U02(N0 2> dissolved in ordinary water, resulted in a homogeneous reactor, having uniformly distributed fuel. This water boiler reactor was spherical. The 235u... 

Package Power Reactors. Several small, compact power reactor plants were developed dufing the period 1957—1962 by the U.S. Army for use ia remote locations. Designed by Alco Products, Inc., the PWRs produced electrical power of about 1 MW along with space heat for military bases. 

Heavy-Water Power Reactors," Proceedings of the International Mtomic Energy Mgeny Symposium, Sept. 11—15,1967, IAEA, Vienna, Austria, 1968. 

Spent Fuel Treatment. Spent fuel assembhes from nuclear power reactors are highly radioactive because they contain fission products. Relatively few options are available for the treatment of spent fuel. The tubes and the fuel matrix provide considerable containment against attack and release of nucHdes. To minimi2e the volume of spent fuel that must be shipped or disposed of, consoHdation of rods in assembhes into compact bundles of fuel rods has been successfully tested. Alternatively, intact assembhes can be encased in metal containers. 

Fig. 2. Volume of low level radioactive waste per U.S. nuclear power reactor (weighted industry median). The decrease over the period 1980—1994 was...

Another safety issue to be considered which might be exacerbated in the reprocessing option is that the plutonium generated in power reactors, called reactor-grade plutonium because it is made up of a variety of plutonium isotopes, contains plutonium-241, which is subject to spontaneous fission (8). The mixture of isotopes makes it extremely difficult to build an effective nuclear weapon. However, an explosive device could be built using this mixture if control of detonation is sacrificed (48). 

In addition, under the Nonproliferation Treaty, which most larger nations have signed, the IAEA monitors plutonium from power reactors so as to detect covert diversion. 

B. Wolfe and D. R. Wilkins, paper presented at ANS Topical Meetings on the Safety of the Next Generation of Power Reactors, Seattie, Wash., May 1988. 

Table 1. Fissile Plutonium Produced in and Separated from Military and Power Reactor Fuel, t...

Includes cumulative amounts from power reactors and spent fuel. 

In plutonium-fueled breeder power reactors, more plutonium is produced than is consumed (see Nuclearreactors, reactor types). Thus the utilisa tion of plutonium as a nuclear energy or weapon source is especially attractive to countries that do not have uranium-enrichment faciUties. The cost of a chemical reprocessing plant for plutonium production is much less than that of a uranium-235 enrichment plant (see Uranium and uranium compounds). Since the end of the Cold War, the potential surplus of Pu metal recovered from the dismantling of nuclear weapons has presented a large risk from a security standpoint. 

Table 4. Isotopic Composition of Plutonium from Thermal Power Reactors — ...

Sodium is used as a heat-transfer medium in primary and secondary cooling loops of Hquid-metal fast-breeder power reactors (5,155—157). Low neutron cross section, short half-life of the radioisotopes produced, low corrosiveness, low density, low viscosity, low melting point, high boiling point, high thermal conductivity, and low pressure make sodium systems attractive for this appHcation (40). 

Total reserves of thorium at commercial price in 1995 was estimated to be >2 x 10 metric tons of Th02 (H)- Thorium is a potential fuel for nuclear power reactors. It has a 3—4 times higher natural abundance than U and the separation of the product from Th is both technically easier and less expensive than the enrichment of in However, side-reaction products, such as and the intense a- and y-active decay products lead to a high... 

Because of its low neutron absorption, zirconium is an attractive stmctural material and fuel cladding for nuclear power reactors, but it has low strength and highly variable corrosion behavior. However, ZircaHoy-2, with a nominal composition of 1.5 wt % tin, 0.12 wt % iron, 0.05 wt % nickel, 0.10 wt % chromium, and the remainder zirconium, can be used ia all nuclear power reactors that employ pressurized water as coolant and moderator (see... 

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