Liquid metals cladding material

Nuclear and magneto-hydrodynamic electric power generation systems have been produced on a scale which could lead to industrial production, but to-date technical problems, mainly connected with corrosion of the containing materials, has hampered full-scale development. In the case of nuclear power, the proposed fast reactor, which uses fast neutron fission in a small nuclear fuel element, by comparison with fuel rods in thermal neutron reactors, requires a more rapid heat removal than is possible by water cooling, and a liquid sodium-potassium alloy has been used in the development of a near-industrial generator. The fuel container is a vanadium sheath with a niobium outer cladding, since this has a low fast neutron capture cross-section and a low rate of corrosion by the liquid metal coolant. The liquid metal coolant is transported from the fuel to the turbine generating the electric power in stainless steel... 

The atomic density of hydrogen in many metal hydrides is greater than that in liquid H2 or in H20. Metal hydrides are efficient moderators (Fig. 1) and neutron shielding materials, and help to minimize the core shield volume. Metal-clad yttrium hydride moderators capable of operation at 1000°C in air, uranium-zirconium hydride rods as a combination fuel-moderator element are examples, and metal-clad zirconium hydride units as moderator elements for operation up to 600°C° °. The hydrogen atom density in hydrides, Ah, the number of hydrogen atoms per cubic centimeter of hydride X 10 , is calculated from the hydrogen-to-metal atom ratio, H/M, the density of the hydride p, and the molecular weight W by ... 

The problem of hyperthermal corrosion resistance of structural materials was got over by development of preliminary protective coatings for the working steel surfaces. In particular, the most important structural units of circuit, e.g. fuel rod claddings and steam generator tubes, are covered by these coatings at the final stage of their manufacture. Additional barriers are also formed directly on the inner surfaces of liquid metal circuit under effect of the coolant in the early stage of the reactor operation. 

The causes and conditions of general achievements and setbacks in reactor and liquid metal coolant technologies are presented in the FRDB, e.g. those determining breeding characteristics (core geometry, fuel enrichment and fissile isotope content, volume fractions, intrinsic limits and smeared density of fuel and blanket pellet, etc), and the fuel bumup limits (chemical composition, fuel fabrication technology, neutron flux, dimensions, cladding and wrapper material, etc.)... 

F.A. Gamer, Irradiation performance of cladding and structural steels in liquid metal reactors, in R.W. Cahn, P. Haasen, E.J. Kramer (Eds.), Material Science and Technology, vol. 10 A, VCH, 1994., volume editor B. R. T. Frost. 

Fast reactor core structures are exposed to various environments during their in-reactor life liquid metal for the exterior surfaces and MOX (U, Pu)02 fuel for the internal layer of the cladding. Moreover, it is also necessary to check the impacts of these materials on the cleaning of fuel assemblies and on fuel reprocessing, especially during fuel dissolution in nitric acid. Only a few results are available on the behavior of ODS alloys in these environments, they can be complemented by results available on ferritic-martensitic steels. The influence of the fine dispersion of nanoparticles on the behavior of ferritic-mattensitic steels in the environment has to be considered. 

This book will introduce the materials considered for the different structural components of the Generation IV systems, under high doses of irradiation such as fuel cladding, wrapper tubes, internal structures, lower doses such as pressure vessel, or no irradiation such as the power conversion systems. It will deal with the behavior in the different environments encountered, liquid metals, molten salts, supercritical water, and gas, as well as the behavior under mechanical stress and irradiation. Subsequently, the different classes of materials for in-core and out-of-core applications will be discussed. 

Based on data obtained so far, it appears that liquid processes in Section III will rely heavily on Ta and Nb alloys as construction materials. Since these metals are expensive in nature and have low yield strength, one must explore different manufacturing means to reduce the overall component cost and enhance the mechanical properties of components. For example, cladding can be used to bond a Ta layer to a base material to take advantage of its corrosion characteristics while keeping the... 

The AGRs are graphite-moderated carbon dioxide-cooled high-temperature reactors that use stainless-steel-clad oxide fuel assemblies. Because of advances in technology, a liquid-salt cooled variant of these reactors appears feasible, provided that the metal components of the fuel assembly are replaced with carbon composite materials. The AGRs are described, as well as a potentially suitable fuel assembly for a liquid-salt variant. 

In both PWRs and BWRs, corrosion of the primary circuit materials is an essential factor in the buildup of contamination layers on the surfaces of the pipes and the components. The materials used in BWRs which are in contact with the reactor water and, therefore, are potential sources of radionuclides are mainly stainless steels wear-resistant hardfacing alloys such as Stellite are also present in most of the plants. Zircaloy as the material of fuel rod claddings, spacers and fuel assembly casks need not be considered in this context, because of the extremely small release of activated constituents from this material. Due to differences in temperature and environment, the mechanisms of the corrosion process and the resulting metal release rates, which contribute to the input of corrosion products into the region of the reactor core, may show differences in different regions of the plant. Thus, corrosion of materials in the water-steam cycle exhibiting H2O phase transformations and considerable temperature differences will proceed differently than in the recirculation lines and the reactor water cleanup system, which are in contact with liquid water exclusively and show comparatively small variations in operating temperature. 

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