Weihua Zhong

The impacts of low dose irradiation on the behavior of electrochemical corrosion and irradiation assisted stress corrosion cracking for 321 stainless steel were studied using Fe²⁺ ion irradiation to simulate neutron radiation damage in primary circuit environment of pressurized water reactor. Low dose irradiation can improve the pitting resistance and reduce the cracking tendency of the alloy in B-Li solution to a certain extent, which was related to the δ phase content on the near-surface of the sample: The higher δ phase content on the near-surface of the 2 dpa irradiated sample was observed by grazing incident X-ray diffraction. In addition, the pits was significantly increased near micro-cracks for the unirradiated sample, indicating that the existence of pits induced the initiation of cracks. The research results provided an important reference for the failure mechanism of irradiation assisted stress corrosion cracking of core components.

High purity SiC crystal was used as a passive monitor to measure neutron irradiation temperature in the 49-2 research reactor. The SiC monitors were irradiated with fast neutrons at elevated temperatures to 3.2 × 10²⁰ n/cm². The isochronal and isothermal annealing behaviors of the irradiated SiC were investigated by x-ray diffraction and four-point probe techniques. Invisible point defects and defect clusters are found to be the dominating defect types in the neutron-irradiated SiC. The amount of defect recovery in SiC reaches a maximum value after isothermal annealing for 30 min. Based on the annealing temperature dependences of both lattice swelling and material resistivity, the irradiation temperature of the SiC monitors is determined to be ∼410 °C, which is much higher than the thermocouple temperature of 275 °C recorded during neutron irradiation. The possible reasons for the difference are carefully discussed.

LT21 a type of aluminum alloy used for the irradiation channel of the first heavy water research reactor (HWRR) in China. Studying the mechanical property of irradiated LT21 aluminum under actual service conditions is essential for evaluating its application property. In this paper, tensile specimens of irradiated LT21 were manufactured from the decommissioned irradiation channel of an HWRR; then, tensile tests were carried out, and then the fracture surfaces were observed. The effect of neutron irradiation on tensile behavior and the failure mechanism was analyzed by comparing the result of irradiated and unirradiated LT21 specimens. The results show that, with the thermal neutron flux increasing to 2.38 × 10²² n/cm², the YS gradually increased from the initial 158 MPa to 251 MPa, the UTS increased from 262 MPa to 321 MPa, and the elongation decreased from 28.8% to about 14.3%; the brittle fracture of the LT21 specimen appeared after irradiation, and the proportion of brittle fracture increased as the neutron fluence increased; the nanophase structures, with a size of less than 50 nm, were precipitated in the LT21 aluminum alloy after neutron irradiation. Transmutation Si is presumed to be the main cause of the radiation effect mechanism of LT21.

The creep behavior of T91 steel at ultrahigh creep temperatures (650–750 °C) at 100 MPa was investigated using small-size specimens, and the related microstructures were characterized. The results showed that the creep failure susceptibility of T91 steel increases significantly as the creep temperature increases from 650 °C to 675 °C. The creep life rapidly decreased from 7880 h to 224 h, and the fracture surface shrinkage increased from 61.9% to 86.5%. Thermodynamic calculations and microstructure observations showed that the increase in creep temperature has a significant effect on the morphology of M₂₃C₆-type carbides, which were distributed around grain boundaries, significantly pinning and hindering the movement of dislocations and the grain boundaries. As the creep temperature increases, the subcrystalline and M₂₃C₆-type carbides significantly coarsen, which is the main reason for the rapidly shortening creep life of T91 steel. This research provides guidance for the material design and microstructure regulation of T91 steel in service at ultrahigh environmental temperatures.