Estimation on Nodular Corrosion Resistance of LWR Cladding by Magnetic Method

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Although the beta-phase has been reported to be a supersaturated solid solution with additives, such as iron, chromium, nickel, and so forth, we have found that Zircaloy-4 after beta-quench is in a superparamagnetic state which contains ferromagnetic intermetallic precipitates so small a few nm that they can not be detected by usual methods. In the case of Zircaloy-2, the phase may be a similar state to Zircaloy-4, but can not be called a superparamagnetic state because of the nonmagnetism of the responsible precipitates.Zircaloy with additive of niobium was also found to be in a superparamagnetic state caused by the precipitates with about 10nm in diameter of ferromagnetic intermetallic compounds. The intermetallic compounds are a quaternary (Zr_<1-x>Nb_x) (Fe_<1-y>Cr_y)_2 as well as (Zr_<1-x>Nb_x) Fe_2 and Zr (Fe_<1-x>Cr_x)_2.Finally, the out of pile corrosion test was performed on the samples of Zircaloy-4, which were heat-treated under the various conditions, such as quenching or furnace-cooling from the temperatures in the temperature range of beta-phase and beta-phase plus alpha-phase of Zirconium. It was found that beta-quench materials of Zircaloy-4 which is in the superparamagnetic state have a corrosion resistant property for "nodular corrosion".