Embrittlement reactors

Properties. Most of the alloys developed to date were intended for service as fuel cladding and other stmctural components in hquid-metal-cooled fast-breeder reactors. AHoy selection was based primarily on the following criteria corrosion resistance in Hquid metals, including lithium, sodium, and NaK, and a mixture of sodium and potassium strength ductihty, including fabricabihty and neutron considerations, including low absorption of fast neutrons as well as irradiation embrittlement and dimensional-variation effects. Alloys of greatest interest include V 80, Cr 15, Ti 5... 

Fusion Reactors. The development of fusion reactors requires a material exhibiting high temperature mechanical strength, resistance to radiation-induced swelling and embrittlement, and compatibUity with hydrogen, lithium and various coolants. One aUoy system that shows promise in this appHcation, as weU as for steam-turbine blades and other appHcations in nonoxidizing atmospheres, is based on the composition (Fe,Co,Ni)2V (30). 

The Tj-carbides are not specifically synthesized, but are of technical importance, occurring in alloy steels, stelUtes, or as embrittling phases in cemented carbides. Other complex carbides in the form of precipitates may form in multicomponent alloys or in high temperature reactor fuels by reaction between the fission products and the moderator graphite, ie, pyrographite-coated fuel kernels. 

Low ambient tern- Monitor temperature perature resulting. adequate heating in embrittlement and/or mechanical design system to accommodate minimum failure of reactor. expected temperature Provide freeze protection/heat tracing CCPS G-23 CCPS G-29 Lees 1996... 

Tube and shell heat exchangers, small distillation columns, reactors, valves, pumps and other items are available in impregnated grapliite. Graphite can be joined only by cementing, which embrittles on aging. It is prone to mechanical damage, particularly when subjected to tensile stresses. 

Basically, tliere are two classes of anunonia converters, tubular and multiple bed. The tubular bed reactor is limited in capacity to a maximum of about 500 tons/day. In most reactor designs, the cold inlet synthesis gas flows tlirough an annular space between the converter shell and tlie catalyst cartridge. This maintains the shell at a low temperature, minimizing the possibility of hydrogen embrittlement, which can occur at normal synthesis pressures. The inlet gas is then preheated to syntliesis temperature by the exit gas in an internal heat e.xchaiiger, after which it enters tlie interior of the anunonia converter, which contains tlie promoted iron catalyst. 

Reactor Component Development — Corrosion of heat-transport tubing — Growth of passive oxides — Hydrogen embrittlement — Surface chloride contamination... 

Lebedev, V. T., Torok, Gy., Didenko, V. I., Lapin, A. N., Petrov, V. A. and Margolin, B. Z (2004) Investigation of nanostructure of reactor pressure vessel steel with different degree of embrittlement, Physica B 350, e471-e474. 

Haber-Bosch process for synthesis of ammonia 1916 Microcracks in the steel reactor were observed due to the reaction of hydrogen with carbon in the steel to produce methane. Mo and Cr were found to prevent hydrogen embrittlement... 

Brittle fracture is always a concern with heavy wall vessels. An 80 to 100°F (27 to 38° C) minimum hydrostatic test temperature is often specified to minimize the possibility of brittle fracture during hydrostatic testing. To minimize the possibility of brittle fracture of heavy wall reactors during start up and shutdown, reduced pressure below 200 to 300° F (90 to 150°C) is usually specified. Typical limitations are 40% of the design pressure or 20% of the original hydrostatic test pressure. With the advent of temper embrittlement resistant steels and weld metal, some refiners feel reduced pressure is only required below 100°F (38°C). 

The metals are employed in a variety of alloys. Lithium generally hardens and strengthens, but also causes embrittlement from 0.05 to 0.1% is used in Al, Zn and Mg alloys. Sodium is an important additive to lead such an alloy is the basis of the manufacture of lead tetraethyl, and another, containing 0.6% Na, 0.6% Ca and 0.05% Li, is a bearing metal. Ternary alloys of caesium with aluminium and either barium or strontium are used in photoelectric cells. Liquid sodium or sodium-potassium alloy is employed to transfer heat from the core of certain atomic reactors, e.g. Dounreay fast breeder. 

Tempered steel is used for the construction of all these pressure reactors, alloyed with chromium and molybdenum to make them resistant to hydrogen under pressure, so that no decarburization, embrittlement and grain boundary splitting occurs. These pressure reactors are more and more being constructed out of several layers. In this way the total reactor wall is built up of a multitude of individual layers, which are wound round a central tube. The advantage of such a multiple layer construction, as against pressure chambers with a plate-girder construction, is that the central tube is subject to chemical demands and the adjacent layers... 

Fast breeder reactor fuel rods consist of stainless-steel-clad mixed oxide (U,Pu)02 fuel however, more stable alloys for cladding and in-core structural materials, with resistance to swelling and embrittlement under fast neutron irradiation, and more efficient fuels (carbide see 17.3.12.1.2) or nitride (see 17.3.12.3)] are needed h The mechanical, metallurgical, and chemical processes in fuel element irradiation are depicted in Figure 1. Figure 2 shows the PFR (U.K.) fast breeder fuel element, and Figures 3 and 4 illustrate the Fast Flux Test Facility (FFTF) fuel system. 

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