| 초록 |
Zr alloys have been used for structural materials of the nuclear system due to their excellent corrosion resistance and extremely small neutron absorption cross-section. The CANDU (CANada Deuterium Uranium) type reactor contains 380 pressure tube channels (in case of CANDU-6 reactor) and chemical composition of the tube is Zr-2.5wt%Nb. A main concern about the Zr-alloys in the nuclear systems is that Zr-based materials are susceptible to the hydrogen-assisted degradation mechanism, such as hydrogen embrittlement and delayed hydrogen cracking. Since integrity of the pressure tube is a key factor of the CANDU reactor safety, behavior of the Zr hydrides in a pressure tube have been extensively investigated in the past forty years. In this study, we assessed presence and amout of phases in the hydrogen charged Zr-2.5Nb pressure tube depending on the temperature. We altered homogenizing heat treatment temperature, as a result, containing hydrogen concentration varies accordingly. We analyzed existing phase and their distribution using the synchrotron XRD, HR-TEM. In the former study, omega-Zr phase are found in Zr-2.5Nb pressure tube. The omega-Zr is known as a metastable phase and it forms under shock pressure condition in the pressure tube. In this study, we evaluated the evolution of omega-Zr phase with respect to the heat treatment temperatures. In general, gamma and delta hydride are observed in hydrogen charged pressure tube. We also characterized the behavior of delta and gamma hydride on the homgenization temperatures. |
