PREDICTION OF DELAYED HYDRIDE CRACK VELOCITY IN THE IRRADIATED ZR-2.5NB CANDU PRESSURE TUBE MATERIALS

摘要

Delayed hydride cracking (DHC) is an important factor to restrict the operation life of pressure tube in CANDU reactor. In this paper DHC behaviors for the pressure tube materials from commercial reactor are reviewed on the effect of neutron irradiation experimentally, and the prediction method of the DHC velocity (DHCV) for the irradiated tube materials is proposed based on the test results of the unirradiated ones. Specimens from the unirradiated and the irradiated tubes, which various amounts of hydrogen is charged through diffusing process, are tested under constant loading condition. The hydride crack grows steadily after incubation time to accumulate hydrogen to crack front, and DHCV's in the irradiated are 4～6 times faster than those of the unirradiated with about 50 kJ in activation energy. According to the irradiation fluence the DHCV has the tendency to be remarkably increased at the initial stages up to 1x10~(25) n/m~2 (E > 1MeV) and saturated with the increase of fluence. The crack velocity in the irradiated can be well predicted from the tensile and DHCV test results for the unirradiated, introducing the acceleration factors according to the yield strength and dissolved hydrogen content due to the neutron irradiation. The DHCV acceleration factor for the yield strength has a tendency to decrease and that for the hydrogen content to increase according to temperature, the proposed equation predict the velocity with 0.12 in standard deviation amount and 95% in coefficient of correlation for the irradiated.