Annealing study on neutron irradiation effects in resonance frequencies of Zircaloy plates by EMAR method

To develop the nondestructive hydrogen concentration measurement method for the irradiated zirconium alloy, the effect of neutron irradiation damage on acoustic properties obtained by the electromagnetic acoustic resonance (EMAR) method was investigated through annealing tests. It is confirmed that the recovery of irradiation damage begins at a lower annealing temperature than that in unirradiated coldworked materials. Unirradiated recrystallization-annealed materials did not show any change in acoustic properties or hardness during the additional RX annealing at 580degC, whereas the acoustic anisotropy (Δf) of the as-cold-worked unirradiated specimen was significantly increased. Four-cycle irradiation clearly decreased the shear wave velocity of the specimen by 1% compared to the RX-annealed specimen. In comparison with the wave velocity change, the acoustic parameters defined in this study are found to be less sensitive to irradiation damage. From the annealing study of the as-irradiated specimens to the RX condition, it is concluded that the absolute value of (Δf) increases by 0.1% and the frequency ratio (fl/fr) by about 0.006 as a result of the damage induced by the four-cycle irradiation in BWRs. These values are applicable to the relationships between the acoustic parameters and hydrogen concentrations of unirradiated materials as the correction factors to compensate the effects of irradiation damage. (author)