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Light water reactors (LWRs) have been generating electricity for over five decades for the electrical grid of more than 20 countries. Most of these reactors are built using a series of alloys and materials that have changed very little over the many decades. The most common structural materials are based on the three elements, iron (Fe), chromium (Cr) and nickel (Ni) such as stainless steels and nickel-based alloys. Most of the Fe-Cr-Ni alloys contain enough Cr to render them passive with low general corrosion in typical LWR environments. Since the chemistry of the water in the reactor is highly controlled, without aggressive impurities such as chloride or sulfate ions, localized corrosion is not a problem for the common structural alloys. The most common failure mode of the Fe-Cr-Ni alloys is environmentally assisted cracking or stress corrosion cracking (SCC), which is currently well understood and successfully mitigated, mainly by dissolving hydrogen gas into the coolant. The other fundamental material in the reactor core is the zirconium-based alloy used for cladding of the fuel rods. The traditional fuel rod alloys were Zircaloy-2 and Zircaloy-4, which were used regularly in boiling water reactor and pressurized water reactor systems, respectively. Very early in the development of the alloys (early 1950s), it was understood that a small amount ( |
