Evaluation of stress corrosion cracking of irradiated 304L stainless steel in PWR environment using heavy ion irradiation

Abstract

International audienceIASCC has been a major concern regarding the structural and functional integrity of core internals of PWR's, especially baffle-to-former bolts. Despite numerous studies over the past few decades, additional evaluation of the parameters influencing IASCC is still needed for an accurate understanding and modeling of this phenomenon. In this study, Fe irradiation at 450 °C was used to study the cracking susceptibility of 304 L austenitic stainless steel. After 10 MeV Fe irradiation to 5 dpa, irradiation-induced damage in the microstructure was characterized and quantified along with nano-hardness measurements. After 4% plastic strain in a PWR environment, quantitative information on the degree of strain localization, as determined by slip-line spacing, was obtained using SEM. Fe-irradiated material strained to 4% in a PWR environment exhibited crack initiation sites that were similar to those that occur in neutron- and proton-irradiated materials, which suggests that Fe irradiation may be a representative means for studying IASCC susceptibility. Fe-irradiated material subjected to 4% plastic strain in an inert argon environment did not exhibit any cracking, which suggests that localized deformation is not in itself sufficient for initiating cracking for the irradiation conditions used in this study

Characterization of ion irradiation effects on the microstructure, hardness, deformation and crack initiation behavior of austenitic stainless steel:Heavy ions vs protons

“…The uncertainty was evaluated to be ± 1dpa and ± 2 dpa, respectively. Irradiation temperature of 450 ± 20 C was used in order to compensate for the effect of higher dose rate (~10 À4 dpa/s for iron ions in comparison to~10 À8 dpa/s for neutrons) on microstructural evolution associated with ion irradiation [24]. Details of the Fe irradiation are given in Refs.…”

“…Details of sample preparation technique are given in Refs. [24,30]. JEOL 2100 HRTEM (High Resolution Transmission Electron Microscope) operated at 200 kV available at UMS Castaing (Toulouse, France) was used for the purpose.…”

“…[16,22e24], authors have shown that dislocation channeling is the prime deformation mode for heavy ion irradiated austenitic stainless steel at PWR relevant temperature as well. However, the strain localization in case of heavy ion irradiated materials has been reported to be less intensive in comparison to its proton irradiated counterparts [16,23,24]. This has been attributed to the shallow penetration depth of heavy ions in austenitic stainless steel [16,23].…”

“…Considering strain localization to be the main contributing factor in IASCC [8e10], shallow penetration depths of heavy ions might greatly affect the IASCC tests by altering the deformation structure at the surface. As a consequence, very few studies related to intergranular cracking in irradiated material are based on the use of heavy ions [24,25], although demonstrating the successful use of heavy ions irradiation in investigating IASCC. Indeed, in a previous study [24], it was shown that iron irradiation on SA 304 L led to intergranular stress corrosion cracking (IGSCC) in PWR environment.…”

“…As a consequence, very few studies related to intergranular cracking in irradiated material are based on the use of heavy ions [24,25], although demonstrating the successful use of heavy ions irradiation in investigating IASCC. Indeed, in a previous study [24], it was shown that iron irradiation on SA 304 L led to intergranular stress corrosion cracking (IGSCC) in PWR environment. Different aspects of intergranular cracking (such as irradiation induced microstructure, irradiation hardening and localized deformation) on iron irradiated material were addressed as well, emphasizing the possibility of using ion irradiation as a tool to investigate IASCC.…”