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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.

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In order to improve sizing accuracy of a pipe discontinuity using ultrasonic guided waves, an analysis method to obtain the reflection coefficients of discontinuity is proposed and the discontinuity-length sizing potential by sweeping frequency is discussed. In this method, reflection coefficients are calculated by integration of reflection waves from divided calculation regions having different characteristic acoustical impedances.The reflection coefficients were analyzed for several shapes of discontinuities on 2-D analysis models, and the reflection coefficients changed cyclically depended on frequency. The effectiveness of the method was confirmed experimentally using torsional mode guided waves (about 40 kHz) that were propagated in pipes with diameters of 60 mm or 114 mm and in which discontinuities (ratio of depth to length = 1:8, 1:16, 1:32) were fabricated.By the results, the trends of analysis results were generally in good agreement with that of experimental results, and the discontinuity-length can be estimated by the relationship between frequency and amplitude, in case that the shape of discontinuity is pre-estimated or assumed.

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