Effect of Neutron Irradiation on the Mechanical Properties of an A508 Cl.2 Forging Irradiated in a BAMI Capsule

The typical operating temperatures of a nuclear reactor pressure vessel in a PWR is typically between ∼290°C and 300°C. However, many BWRs and some PWRs operate at slightly lower temperatures down to 275°C. Most of the literature and neutron irradiation damage is therefore focused on those irradiation temperatures. It is well-known that the lower the irradiation temperature, the more neutron irradiation damage occurs, because no appreciable annealing occurs at approximately 230°C. The NOMAD-0 irradiation campaign at the BR2 was a preliminary irradiation specifically designed to determine the appropriate irradiation conditions that result in specific irradiation damage levels of an A508 Cl.2 grade at lower temperatures than the usual PWR operating temperature window. The BAMI capsules with controlled He gas gap were used for this irradiation. To avoid temperature gradients from the outside to the center of the cylindrical blocks, the latter were limited in size. Only tensile and fracture toughness data could therefore be obtained with mini-tensile and mini-CT specimens. The results show that no influence of the temperature gradient could be found on the tensile and fracture toughness properties. The specimen size and geometry on the fracture toughness results was analyzed and discussed. The effect of irradiation temperature on the tensile properties and the transition temperature as determined by the master curve approach on the mini-CT samples is discussed.