Abstract
Developing the model for simulating radiation induced segregation (RIS) process, investigating the effect of proton irradiation on RIS and stress corrosion cracking propagation are the objectives of this study. The RIS model which is based on inverse Kirkendall effect incorporates radiation damage rate effect, atom-defect coupling effect, and interstitial-vacancy pair loss term toward dislocations, and therefore can predicts the RIS concentration profile of irradiated SEN304SS and AR304SS reasonably. According to the thermodynamic parameters benchmarked in proton irradiation data, the updated RIS can be extended to evaluate the Cr depletion evolution in neutron irradiated materials. Experimental works include proton irradiations on SEN304SS and AR304SS in tandem accelerator, grain boundary microchemistry examinations by FEG-TEM/EDX, SCC crack growth rate measurements by RDC and ECN techniques. The repassivation kinetics is analyzed for elucidating the cracking mechanism of irradiation assisted stress corrosion cracking. Electrochemical noise technique failed to measure the propagation of stress corrosion crack, both under load application by passive bolt loaded and active tension loaded. Applying ZrO2 coating to shielding extra surface, and shorten the distance between counter and working electrodes made no improvements. The anodic current in crack tip was probably consumed on the crack flank, or couldn’t flow out toward counter electrode because of high impedance of the testing solution. Reversing DC techniques successfully measured the crack propagation of proton irradiated stainless steels. The crack growth rate is enhanced by proton irradiation, but also affected by prior heat treatments. The Cr depletion rate was enhanced by irradiation when initial grain boundary Cr concentration was enriched before irradiation (in SA condition), but radiation induced Cr decrement developed more slowly if the initial Cr concentration was depleted (in SEN condition). The intergranular crack growth rate of proton irradiated SS correlates linearly with the Cr concentration at grain boundary regardless of its prior thermal or irradiation histories. The EPR value can be treated as a qualitative indicator to evaluate the crack growth rate of proton irradiated SS304 with different prior thermal treatments. In simulating BWR environments of oxygen saturated or normal water chemistry, Irradiation assisted stress corrosion cracking are affected by radiation sensitization, solution conductivity and ECP. The protection ECP is -200mVSHE for proton irradiated SEN304 stainless steel. The IASCC growth rate was reasonably predicted by PLEDGE model which was developed on the basis of film rupture/metal dissolution mechanism. Repassivation kinetics analysis verified that radiation sensitization alter the repassivation ability and consequently enhance the stress corrosion crack propagation. The crack growth rate of proton irradiated stainless steel can be predicted by converting the repassivation current according to film rupture/metal dissolution model. However, irradiation affects not only repassivation current, but also film rupture frequency. Three future studies are suggested. 1. Increase the radiation dose and irradiation depth. Investigate the effect of higher radiation dose on the SCC cracking behavior. 2. Refine RIS model by considering thermal and radiation sensitization coupling effect, FMD source term, and incorporating high dose effect of creep and void. 3. Perform the SCC test of irradiated stainless steel at various temperatures.