Fission, nuclear reactors using

Some nuclear reactors use heavy water to slow down neutrons produced during nuclear fission. Heavy water contains deuterium, an isotope of hydrogen. What is the mass number of deuterium ... 

Hafnium has a great affinity for absorbing slow neutrons. This attribute, along with its strength and resistance to corrosion, makes it superior to cadmium, which is also used for making control rods for nuclear reactors. This use is of particular importance for the type of nuclear reactors used aboard submarines. By moving the control rods in and out of a nuclear reactor, the fission chain reaction can be controlled as the neutrons are absorbed in the metal of the rods. The drawback to hafnium control rods is their expense it costs approximately one million dollars for several dozen rods for use in a single nuclear reactor. 

Fuel Element. Any material which may undergo the appropriate reaction and be the source of energy in a fusion or fission nuclear reactor is known as nuclear fuel At the present state of technology such fuels are uranium, thorium or plutonium, either as natural materials or enriched or synthesized isotopes of these elements. They are used as solns or as solids (metals, oxides, or carbonates) shaped as plates, rods etc and known as fuel element (fuel plate or fuel rod)... 

Unfortunately, no one has figured how to make the process work on a large scale. One nuclear reactor using thorium was built near Platteville, Colorado, in 1979. However, a number of economic and technical problems developed. After only 10 years of operation, the plant was shut down. The promise of thorium fission plants has yet to become reality. 

The physical properties of isotopes differ slightly because of differences in atomic mass. For example, water that contains deuterium is called heavy water because the neutrons in deuterium add mass to the water molecule. Some nuclear reactors use heavy water to help keep the chain reaction going. The heavy water slows down (or moderates) the neutrons produced during nuclear fission so that they can be absorbed by the uranium fuel. You will learn more about nuclear reactions in Chapter 25. 

Research nuclear reactors use thermal neutrons to induce fission in a critical mass of to produce high-energy (fast, or hot) neutrons ... 

Nuclear reactors use the heat from a controlled nuclear fission reaction to produce power. The three important types of reactors are light water reactors, heavy water reactors, and breeder reactors. 

Current nuclear reactors use fission to produce electrical energy. 

Radioactive nuclei emit a particles, 13 particles, positrons, or y rays. The equation for a nuclear reaction includes the particles emitted, and both the mass numbers and the atomic numbers must balance. Uranium-238 is the parent of a natural radioactive decay series. A number of radioactive isotopes, such as and C, can be used to date objects. Artificially radioactive elements are created by the bombardment of other elements by accelerated neutrons, protons, or a particles. Nuclear fission is the splitting of a large nucleus into smaller nuclei plus neutrons. When these neutrons are captured efficiently by other nuclei, an uncontrollable chain reaction can occur. Nuclear reactors use the heat... 

A major form of fuel for nuclear reactors used to produce electrical energy is a fissionable isotope of plutonium. Plutonium is a transuranium element. Why is this element used instead of a fissionable isotope that occurs in nature ... 

A chain reaction continues until all of the uranium-235 atoms have split or until the neutrons fail to strike other uranium-235 nuclei. If the mass of the uranium-235 sample is helow a certain minimum, too many neutrons escape without striking other nuclei, and the chain reaction stops. The minimum amount of nuclide that provides the number of neutrons needed to sustain a chain reaction is called the critical mass. Uncontrolled chain reactions give the explosive energy to atomic bomhs. Nuclear reactors use controlled-fission chain reactions to produce energy and radioactive nuclides. 

Nuclear reactors use the heat from a controlled nuclear fission reaction to produce power. Fission is controlled, in part, by moderators— materials that fimit the speed of liberated neutrons but that do not themselves undergo fission when bombarded with neutrons. The three important types of reactors are light water reactors, heavy water reactors, and breeder reactors. Breeder reactors produce more fissionable material than they consume. 

SiCf/SiC ceramic matrix. composites (CMC) are considered as structural materials in next generation fission nuclear reactors. However, thermal conductivity of SiC is reduced on the one hand at the highest temperatures, but also under irradiation. Titanium carbide, because of its peculiar thermal properties is an attractive material to be used as a matrix in a CMC to enhance the thermal conductivity of CMC under irradiation and at high temperature. 

To produce power, a fission nuclear reactor requires fissile material. Generation II or in reactors (pressurized water reactor [PWR], CANDU, evolutionary power reactor [EPR], etc.), being imder-breeder systems (ie, using more fissile material than they... 

Spent fuel can be stored or disposed of intact, in a once-through mode of operation, practiced by the U.S. commercial nuclear power industry. Alternatively, spent fuel can be reprocessed, ie, treated to separate the uranium, plutonium, and fission products, for re-use of the fuels (see Nuclear REACTORS, CHEMICAL reprocessing). In the United States reprocessing is carried out only for fuel from naval reactors. In the nuclear programs of some other countries, especially France and Japan, reprocessing is routine. 

Water as coolant in a nuclear reactor is rendered radioactive by neutron irradiation of corrosion products of materials used in reactor constmction. Key nucHdes and the half-Hves in addition to cobalt-60 are nickel-63 [13981 -37-8] (100 yr), niobium-94 [14681-63-1] (2.4 x 10 yr), and nickel-59 [14336-70-0] (7.6 x lO" yr). Occasionally small leaks in fuel rods allow fission products to enter the cooling water. Cleanup of the water results in LLW. Another source of waste is the residue from appHcations of radionucHdes in medical diagnosis, treatment, research, and industry. Many of these radionucHdes are produced in nuclear reactors, especially in Canada. 

The only large-scale use of deuterium in industry is as a moderator, in the form of D2O, for nuclear reactors. Because of its favorable slowing-down properties and its small capture cross section for neutrons, deuterium moderation permits the use of uranium containing the natural abundance of uranium-235, thus avoiding an isotope enrichment step in the preparation of reactor fuel. Heavy water-moderated thermal neutron reactors fueled with uranium-233 and surrounded with a natural thorium blanket offer the prospect of successful fuel breeding, ie, production of greater amounts of (by neutron capture in thorium) than are consumed by nuclear fission in the operation of the reactor. The advantages of heavy water-moderated reactors are difficult to assess. 

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