International round robin onion irradiation of alloy T91 and comparison with neutron irradiation

An international collaboration was established as a Coordinated Research Project (CRP) under the IAEA and entitled Accelerator Simulation and Theoretical Modelling of Radiation Effects-II (SMoRE-II). It was created to determine, by way of a Round Robin process, the degree to which ion irradiations produced the same irradiated microstructure when conducted in different labs on the same alloy and provided with the same irradiation protocol. The Round Robin consisted of 13 participating organizations from 9 IAEA member states with ion irradiations conducted at all CRP partner sites on samples of a single alloy (T91) from a single billet with the same thermal-mechanical history, and with a specific protocol for conducting the irradiations. Of the 14 parameters specified for the ion irradiations, only 1 of 12 facilities was able to follow the protocol exactly. Major differences included vacuum pressure, temperature measurement and control, beam mode (raster-scanning vs. steady beam), and dosimetry. The microstructure features characterized were the sizes and number densities of cavities, dislocation loops, precipitates, and the radiation induced segregation. While loop size and number density appeared to correlate with carbon content, no such correlation was identified for cavities. The divergence from the irradiation protocol undoubtedly affected the irradiated microstructure with carbon contamination occurring in most cases. The cavity, dislocation loop and precipitate microstructures all fell within the range of that in the literature. Additionally, a T91 sample that was irradiated to 47 dpa at 376◦C in the BOR-60 reactor was selected for comparison of the microstructure to those in the Round Robin study.