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Reactions of Ni and Co ions with amorphous iron (ill) hydroxide, which was synthesized by electrolysis of iron electrode, have been studied in high temperature water using an in situ method of a modified magnetic balance and using a reaction model. Formation of NiFe,O. and CoFe 2 0 4 from the amorphous iron (ill) hydroxide were explained by the reaction model incorporating two phenomena, i.e. dehydration of the iron(ill) hydroxide and diffusions of Ni and Co ions into it. The dehydration rate followed Avrami's equation. Apparent activation energy of the dehydration was 4.39 x 10 4 J/mol for the amorphous iron (ill) hydroxide used in the experiments. The diffusions of Ni and Co ions into the particle were evaluated from the diffusion equation for spherical coordinates. The diffusion coefficient of Ni ion into the amorphous iron(ill) hydroxide was much higher than that of Co ion, while its apparent activation energy was about 5.5 x 10 4 J/mol, a value close to that of Co ion. However, the diffusion rate of Co ion into a-Fe,O, was faster than that of Ni ion. Calculated values from the reaction model showed good agreement with experimental values.

The effects of hydrazine on the corrosion of Zircaloy-2 were examined in supercritical water. Hydrazine could be used as a reducing agent to control the corrosive environment for the coolant of boiling water reactors (BWRs). Before the corrosion test, the applicability of supercritical water for corrosion testing of zirconium alloys was studied. Supercritical water was found to be a useful solvent for testing corrosion based on the following facts: (1) the weight gain of Zircaloy-2 in supercritical water followed the same cubic law with the activation energy of 133 kJ/mol as that in water and steam did, and (2) the weight gain in supercritical water at 723 K and 24.5 MPa was more than 8 times greater than that in water at 561 K and 7.8 MPa depending on immersion time. The corrosion tests in supercritical water at 723 K and 24.5 MPa under -irradiation for 1,000 h were conducted to study the effects of adding nitrogen and ammonia on the corrosion of Zircaloy-2. Nitrogen and ammonia are decomposed products of hydrazine. The measured weight gain, oxide film thickness, and amount of hydrogen pick-up had slight differences between cases with and without the additives. Based on these data, it was concluded adding hydrazine to the coolant has little influence on the corrosion of Zircaloy-2 used in BWR cores.