Irradiation tests of a BWR advanced Zr alloy (HiFi alloy) and Zircaloy-2 (Zry-2) were carried out in a Japanese commercial reactor and the irradiation performances of the materials were investigated. HiFi alloy and Zry-2 showed excellent resistance to corrosion up to 70 GWd/t, and furthermore, HiFi kept lower hydrogen pickup compared with Zry-2. TEM observation showed that the Fe/(Fe+Cr) ratio of Zr(Fe,Cr) 2 type second phase particles (SPPs) for HiFi alloy and Zry-2 tended to decrease as fast neutron fluence increased and to saturate at high fluence. Zr-Fe-Cr SPPs did not completely disappear even for 6 cycles for the irradiated HiFi alloy and Zry-2. In order to clarify the mechanism of hydrogen absorption, an electrochemical technique was used for the oxide film of both materials as part of the out-ofpile test. The relation between the oxide surface potential and the hydrogen pickup fraction was estimated suggesting that the potential difference over the oxide film suppressed hydrogen (proton) diffusion in the oxide film.
In order to study the applicability of EMAR (electromagnetic acoustic resonance) method to non-destructive hydrogen level assessment in fuel spacer bands at pool side, an ultrasonic transmitter and receiver together with an EMAT (electromagnetic transducer) were used. Unirradiated Zircaloy-2 thin plates were hydrogen charged for the measurements. An irradiated fuel cladding tube was also used to examine the detection sensitivity of the resonance spectrum of the irradiated material. The following results were obtained. Acoustic anisotropy Á f , defined by using two resonance frequencies for shear waves with different polarization, was adopted as a parameter to express the ultrasonic resonance property. A hydrogen concentration dependence of Á f was observed in the range up to 1,200 ppm. Specimen thickness and oxide thickness were found to have negligible effect, on Á f , and liftoff of the sensor up to 1 mm did not affect the Á f value. The acoustic anisotropy proposed in this paper was not sensitive to any of specimen dimension, surface condition, or sensor liftoff.
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