Environmental Degradation of Materials in Advanced Reactors
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Degradation of Materials in Advanced Reactors
C. Cabet, J. Jang, J. Konys, and P.F. Tortorelli Abstract Advanced fission-based reactors challenge our ability to fully understand environment–materials reactions in terms of fundamental stability and kinetics, including the influences of composition, microstructure, and system design, and to predict associated long-term performance. This article briefly describes corrosion reactions and the processes by which such are managed for several elevated-temperature environments associated with advanced reactor concepts: helium, molten Pb–Bi, fluorides, and supercritical water. For most of the subject environments, corrosion resistance critically depends on the ability to form and maintain protective surface layers. Effects of corrosion on mechanical behavior can be from thermally and chemically induced changes in microstructures or from environmental effects on cracking susceptibility. In most cases, the simultaneous effects of chemical reactivity and radiation have not been fully addressed, nor has much attention been paid to newly emerging alloy compositions or the effects of substantially increased operating temperatures.
Introduction All materials will degrade to various degrees and in various ways under the environmental conditions anticipated for advanced fission-based reactors. This article focuses on three types of fluids of interest for advanced reactors that challenge our fundamental knowledge of materials stability and reaction dynamics, as well as our related ability to properly design materials and systems for long-term compatibility and integrity in these and other aggressive environments. Environmental degradation in nuclear systems is of particular concern, not only because of the potential consequences of a materials or system failure induced by corrosion wastage and/or environmentally induced cracking, but also because of the difficulty of the research problem. Specifically, the reactive fluids that comprise the exposure environments of the structure and cladding materials typically operate nonisothermally. This imposes a set of additional driving forces for corrosion and mass transfer that can exacerbate
degradation and introduce additional reaction pathways. These factors take on even more importance for the environments addressed in this article because, compared to conventional light water reactors, the maximum temperatures are higher and, more generally, the reactivity of these fluids are more aggressive toward many materials. In addition, the effects of radiation damage and/or heat flux (for cladding and heat exchanger materials) on the dynamics of materials degradation must also be considered. However, this article will not address these latter effects in any detail because relatively little work has been focused on such effects for the subject fluids.
Helium For high temperatures, helium gas is an excellent heat-transfer fluid (coolant), because it can be used at low pressures and undergoes no phase transitions. This simplifies the engineering/d
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