Status report on project MICRIN, Mitigation of Crack Initiation

Environmentally assisted cracking, EAC, is one of the major degradation modes in nuclear power plants. Good knowledge has been achieved on parameters influencing EAC crack growth, and disposition curves for EAC crack growth rates in especially BWR and BWRIHWC conditions are available for low alloy steels, stainless steels and many Ni-based alloys. EAC is the result of a combination of a susceptible material, environment and stress. Multitudes of affecting parameters are known and their influence on crack growth rate has been quantified. A white paper on crack initiation of structural materials in LWRs was written within the NULl FE project in 2011, after which a EU project proposal was prepared. This proposal was, however not approved for funding, and the decision was made between the partners to start an in-kind project, MICRIN, mitigation of crack initiation. Simultaneously, investigations on initiation susceptibility have been performed in the SAFIR2014 ENVIS project on nickel-based materials. The MICRIN project suits thus well within the scope of ENVIS. The main objective of the MICRIN project is to develop an accelerated test method for stress corrosion cracking initiation. The accelerated test should be able to find stress thresholds for crack initiation for some relevant corrosion systems and ways to mitigate the crack initiation. The accelerated test technique proposed is the use of a tapered specimen. Tailored, Sidoped stainless steel, also used in the PERFORM60 project is available at SCK-CEN. This report gives the status of the MICRIN project, the time schedule of which has been delayed due to delays in specimen manufacturing.