Nuclear power reactor generations

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. 

A nuclear power plant generates electricity in a manner similar to a fossil fuel plant. The fundamental difference is the source of heat to create the steam that turns the turbine-generator. A fossil plant relies on the combustion of natural resources (coal, oil) to create steam. A nuclear reactor creates steam with the heat produced from a controlled chain reaction of nuclear fission (the splitting of atoms). 

Because the isotope uranium-235 is fissionable, meaning that it produces free neutrons that cause other atoms to split, it generates enough free neutrons to make it unstable. When the unstable U-235 reaches a critical mass of a few pounds, it produces a self-sustaining fission chain reaction that results in a rapid explosion with tremendous energy and becomes a nuclear (atomic) bomb. The first nuclear bombs were made of uranium and plutonium. Today, both of these fuels are used in reactors to produce electrical power. Moderators (control rods) in nuclear power reactors absorb some of the neutrons, which prevents the mass... 

The most important apphcation of this metal is as control rod material for shielding in nuclear power reactors. Its thermal neutron absorption cross section is 46,000 bams. Other uses are in thermoelectric generating devices, as a thermoionic emitter, in yttrium-iron garnets in microwave filters to detect low intensity signals, as an activator in many phosphors, for deoxidation of molten titanium, and as a catalyst. Catalytic apphcations include decarboxylation of oxaloacetic acid conversion of ortho- to para-hydrogen and polymerization of ethylene. 

Plutonium is the most important transuranium element. Its two isotopes Pu-238 and Pu-239 have the widest applications among all plutonium isotopes. Plutonium-239 is the fuel for nuclear weapons. The detonation power of 1 kg of plutonium-239 is about 20,000 tons of chemical explosive. The critical mass for its fission is only a few pounds for a solid block depending on the shape of the mass and its proximity to neutron absorbing or reflecting substances. This critical mass is much lower for plutonium in aqueous solution. Also, it is used in nuclear power reactors to generate electricity. The energy output of 1 kg of plutonium is about 22 million kilowatt hours. Plutonium-238 has been used to generate power to run seismic and other lunar surface equipment. It also is used in radionuclide batteries for pacemakers and in various thermoelectric devices. 

The radioactive wastes associated with nuclear reactors fall into two categories (1) commercial wastes — the result of operating nuclear-powered electric generating facilities and (2) military wastes—the result of reactor operations associated with weapons manufacture, Because the fuel in plutonium production reactors, as required by weapons, is irradiated less than the fuel in commercial power reactors, the military wastes contain fewer fission products and thus are not as active radiologically or thermally. They are nevertheless hazardous and require careful disposal. 

Nuclear fission reactors ( nuclear power reactors ) are devices that use controlled neutron-induced fission to generate energy. While a complete description of the design of these devices is beyond the scope of this book, there are certain basic principles related to nuclear reactors that are worth studying and that can be described and understood with a moderate effort. 

Boiling Water Reactor A type of nuclear power reactor that uses ordinary water for both the coolant and the neutron moderator. The steam is used to directly produce electricity through generators. 

As of November 29, 1978, there were 72 operating nuclear power reactors in the United States with generating capacity of 52,273 megawatts (MWe). The total number of plants committed is 203 with a total capacity of 197,918 MWe. 

Pii (about 2.2 kg), -" Pu (about 1.1 kg) and " Pu (about 0.4 kg) are generated by (n, y) reactions from Pii. Pu is a valuable nuclear fuel and may also be used for production of nuclear weapons. The global production rate of Pu in nuclear power reactors is of the order of 100 tons per year contained in spent fuel elements. Non-proliferation agreements should prevent uncontrolled distribution of Pu. Moreover, Pu is highly toxic. Am and Cm arc generated in smaller amounts in nuclear reactors by (n, /) reactions (about 0.15 kg Am and about 0.07 kg Cm per ton of spent fuel after a burn-up of 35 000 MW d per ton). 

Much of the impetus for the awakened interest and utilization of inorganic membranes recently came hom a history of about forty or fifty years of some large scale successes of porous ceramic membranes for gaseous diffusion to enrich uranium in the military weapons and nuclear power reactor applications. In the gaseous diffusion literature, the porous membranes are referred to as the porous barriers. For nuclear power generation, uranium enrichment can account for approximately 10% of the operating costs (Charpin and Rigny, 1989]. 

The primary use for plutonium (Pu) is in nuclear power reactors, nuclear weapons, and radioisotopic thermoelectric generators (RTGs). Pu is formed as a by-product in nuclear reactors when uranium nuclei absorb neutrons. Most of this Pu is burned (fissioned) in place, but a significant fraction remains in the spent nuclear fuel. The primary plutonium isotope formed in reactors is the fissile Pu-239, which has a half-life of 24 400 years. In some nuclear programs (in Europe and Japan), Pu is recovered and blended with uranium (U) for reuse as a nuclear fuel. Since Pu and U are in oxide form, this blend is called mixed oxide or MOX fuel. Plutonium used in nuclear weapons ( weapons-grade ) is metallic in form and made up primarily (>92%) of fissile Pu-239. The alpha decay of Pu-238 (half-life = 86 years) provides a heat source in RTGs, which are long-lived batteries used in some spacecraft, cardiac pacemakers, and other applications. 

Fig. 1 Progressive development of successive generations of nuclear power reactors. http //upload.wikimedia.org/wikipedia/ commons/4/4e/GenIVRoadmap.jpg.

The fuel processing operations to be used in conjunction with a nuclear power reactor and the amount of nuclear fuel that must be provided depend on the type of reactor and on the extent to which fissile and fertile constituents in spent fuel discharged from the reactor are to be recovered for reuse. Figures 1.10 and 1.11 outline representative fuel processing flow sheets for uranium-fueled thermal reactors generating 1000 MW of electricity, at a capacity factor of 80 percent. 

Nuclear Energy Reactors An uncontrolled fission chain reaction can be adapted to make an atomic bomb, but controlled fission can produce electric power more cleanly than can the combustion of coal. Like a coal-fired power plant, a nuclear power plant generates heat to produce steam, which turns a turbine attached to an electric generator. 

In Germany in 1938, Otto Hahn and Fritz Strassmann, skeptical of claims by Enrico Fermi and Irene Johot-Curie that bombardment of uranium by neutrons produced new so-called transuranic elements (elements beyond uranium), repeated these experiments and chemically isolated a radioactive isotope of barium. Unable to interpret these findings, Hahn asked Lise Meitner, a physicist and former colleague, to propose an explanation for his observations. Meitner and her nephew, Otto Frisch, showed that it was possible for the uranium nucleus to be spfit into two smaller nuclei by the neutrons, a process that they termed fission. The discovery of nuclear fission eventually led to the development of nuclear weapons and, after World War II, the advent of nuclear power to generate electricity. Nuclear chemists were involved in the chemical purification of plutonium obtained from uranium targets that had been irradiated in reactors. They also developed chemical separation techniques to isolate radioactive isotopes for industrial and medical uses from the fission products wastes associated with plutonium production for weapons. Today, many of these same chemical separation techniques are being used by nuclear chemists to clean up radioactive wastes resulting from the fifty-year production of nuclear weapons and to treat wastes derived from the production of nuclear power. 

All nuclear power reactors outside the previous USSR and CMEA countries have a reactor containment building, the purpose of which is to contain steam and released radioactivities in case of a severe accident, and to protect the reactor from external damage. The contairunent is designed (and tested) to withstand the internal pressure from a release of the water in the entire primary cooling circuit (and in the case of PWRs of the additional loss of one of the steam generators), corresponding to excess pressures of 0.4 MPa. The containmrat is provided with a spray, which cools and condenses the steam released and... 

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