Effects of Reactor Exposure on Nuclear Fuel Cladding

摘要

In face of increasing worldwide demand for electricity generation and the increasing concerns with the contribution of fossil fuel emissions to climate change, nuclear power is again being considered for further development in the US and abroad. New reactor construction is being proposed, using, both, evolutionary concepts based on the current fleet of Light Water reactors (LWRs) and advanced reactor concepts such as those proposed under the Generation Ⅳ initiative. The materials used in these reactors have to maintain outstanding performance for years or even decades, in an extreme environment, in which they are exposed to a combination of high temperature and pressures, aggressive chemistry and a constant fast neutron flux. Among the many materials used in reactor core are metallic alloys which are used for nuclear fuel cladding, structural materials and for the pressure vessel. Under neutron irradiation atomic displacements are generated in these materials, causing the steady state defect concentration to be highly supersaturated relative to thermal equilibrium conditions. As a result, under irradiation these materials are very far from equilibrium, allowing configurations to be observed that are not seen outside irradiation. Phenomena such dimensional instability (irradiation creep and growth and void swelling), mi-crochemical evolution (irradiation-induced segregation), irradiation dissolution of stable phases and precipitation from un-dersaturated solid solution can be observed depending on the relative balance between damage and annealing. In addition, chemical degradation caused by exposure to high temperature water can cause phenomena such as general corrosion, hy-driding, stress corrosion cracking, crud deposition and localized forms of corrosion such as nodular corrosion and shadow corrosion and fuel-clad interactions. These microstructural changes can severely affect fuel cladding properties, such as strength, ductility, corrosion resistance and fracture toughness. As utilities and fuel vendors attempt to push materials to higher temperatures and doses many challenges become apparent in all these areas. These concepts and challenges will be reviewed in this talk as well as the opportunities to use current advances in computational techniques and new experimental tools and techniques to understand these processes in a more fundamental manner.