Materials for nuclear reactors

The raw material for nuclear reactor fuel, uranium, exits the mining—milling sequence as uranium oxide. Because of its color, it is called yellow cake. The yellow cake is converted to uranium hexafluoride and enriched in 235u... 

T. D. Burchell, M. O. Tucker and B. McEnaney. Qualitative and Quantitative Studies of Fracture in Nuclear Graphites, Materials for nuclear reactor core applications. BNES, London, 1987, pp. 95-103. 

Either MA or MM processes drop under more general class of solid-state amorphization reactions, SSAR. Amorphization by irradiation of solids was observed yet in the era of study of materials for nuclear reactors. In 1962, Bloch [88] amorphized UgFe by exposing it to fluxes of nuclear fission fragments. Others obsawed amorphization... 

It is used in lamp filaments flash bulbs vacuum tubes and in explosives. It is also used as a structural material for nuclear reactors. 

Hydrogen embrittlement is a problem with zirconium and zirconium alloys, which often are used as cladding materials for nuclear reactors. Zirconium reacts with water as follows. 

D. Gilbon, et al., in Bristol Conference, Materials for Nuclear Reactor Core Applications 1, BNES, 1987, pp. 307-312. 

L. DeWilde, J. Gedopt, S. DeBurbure, A. Delbrassibe, C. Driesen, B. Kazimierzak, in Proceeding in Materials for Nuclear Reactor Core Applications BNES London, 1987, pp. 271-276. 

Regarding stainless steels, type 304 stainless steel was used in early PWRs and type 316L has been used in LMFBRs. Stainless steels also have been extensively used as ex-core structural materials for nuclear reactors. Stress corrosion cracking (SCC) may become a problem when stainless steels are used as cladding materials. This problem should be carefully considered in the Super LWR. On the other hand, from the long experience of supercritical FPP operations, SCC has not been a problem. 

The isotope boron-10 is used as a control for nuclear reactors, as a shield for nuclear radiation, and in instruments used for detecting neutrons. Boron nitride has remarkable properties and can be used to make a material as hard as diamond. The nitride also behaves like an electrical insulator but conducts heat like a metal. 

Cold-roUed alloys of lead with 0.06 wt % teUurium often attain ultimate tensile strengths of 25—30 MPa (3625—5350 psi). High mechanical strength, excellent creep resistance, and low levels of alloying elements have made lead—teUurium aUoys the primary material for nuclear shielding for smaU reactors such as those aboard submarines. The aUoy is self-supporting and does not generate secondary radiation. 

Low sulfur and ash levels are required for high GTE, isotropic cokes used for carbon and graphite specialty products. Highly isotropic cokes are also the filler materials for producing graphite for nuclear reactors. The purity, particularly the boron content, is critical in this appHcation. Properties of typical needle and isotropic (regular) cokes are summarized in Table 1. 

Nonferrous alloys account for only about 2 wt % of the total chromium used ia the United States. Nonetheless, some of these appHcations are unique and constitute a vital role for chromium. Eor example, ia high temperature materials, chromium ia amounts of 15—30 wt % confers corrosion and oxidation resistance on the nickel-base and cobalt-base superaHoys used ia jet engines the familiar electrical resistance heating elements are made of Ni-Cr alloy and a variety of Ee-Ni and Ni-based alloys used ia a diverse array of appHcations, especially for nuclear reactors, depend on chromium for oxidation and corrosion resistance. Evaporated, amorphous, thin-film resistors based on Ni-Cr with A1 additions have the advantageous property of a near-2ero temperature coefficient of resistance (58). 

The proper choice of material is now a quite different one. Reinforced concrete is now the best choice - that is why many water towers, and pressure vessels for nuclear reactors, are made of reinforced concrete. After that comes pressure-vessel steel - it offers the best compromise of both price and weight. CFRP is very expensive. 

For the purpose of this discussion, radiological materials that could be used in a terrorist attack are divided into three categories (1) bomb-grade nuclear material, (2) nuclear reactor fuel and associated waste products, and (3) industrial sources. Bomb-grade nuclear material includes concentrated plutonium and/or highly enriched uranium (>20% U-235) that may be used to build a nuclear weapon, assuming a terrorist group cannot or has not already secured an assembled weapon. 

A single kilogram of radioactive metallic plutonium-238 produces as much as 22 million kilowatt-hours of heat energy. Larger amounts of Pu-238 produce more heat. However, Pu-238 is not fissionable, and thus it cannot sustain a chain reaction. However, plutonium-239 is fissionable, and a 10-pound ball can reach a critical mass sufficient to sustain a fission chain reaction, resulting in an explosion, releasing the equivalent of over 20,000 tons of TNT. This 10-pound ball of Pu-239 is only about one-third the size of fissionable uranium-235 required to reach a critical mass. This makes plutonium-239 the preferred fissionable material for nuclear weapons and some nuclear reactors that produce electricity. 

Structural materials for fission reactors (as well as for future fusion reactors) are being exposed to intense neutron flux for many years. In the case of fusion reactor, 14-MeV neutrons, produced by the fusion reaction of d + t He + n, induce nuclear reactions of... 

Hausner S.B.Roboff, "Materials for Nuclear Power Reactors," ReinhoM, Y J9VD 45)F.G.Brickweddi f "To..spi/.-,is ure in Atomic... 

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