Warm Pre-Stress Effect Measured at Irradiated RPV Weld Material

The recently initiated German project CARISMA (Crack Initiation and Arrest of Irradiated Steel Materials) will create a data base on pre-irradiated original materials of the four generations of German nuclear pressurized water reactors, which allows the examination of the consequences if the Master Curve instead of the RT_NDT concept is applied. Several original materials of the four generations of German nuclear power plants (typical for KWO, KKS - Biblis A, Biblis B, KKU - KKG, KWG, KKP2, KBR - KKE, KK12, GKN2) will be investigated. They have been irradiated in six large scale irradiation capsules in a German research reactor (the VAK plant) at corresponding plant conditions. The capsules contain regular tensile and Charpy impact specimens as well as Pellini and fracture toughness wedge opening load specimens up to a specimen thickness of 100 mm. The first fracture toughness tests have been performed on a weld metal NiCrMo1 UP(mod.)/LW320, LW340 (1. generation, lower bound of the weld materials)—with a fluence Φ = 2,12E19 cm⁻² (E > 1 MeV). This weld has a Cu-content of 0.22 wgt.% and it was therefore supposed to show a large transition temperature shift. Some fracture toughness tests in the irradiated material condition were already available and during this project four 100 mm thick wedge opening load (WOL) specimens were tested. At one of the specimens brittle failure could not be achieved during the test, because the load capacity of the test machine was exceeded. Therefore the specimen was loaded by a load-unload-cool-fracture load path to demonstrate the warm pre-stress effect of this highly irradiated specimen. At the final fracture of the specimen at a lower temperature, the failure load was significantly higher than the original one (factor 3 higher), which clearly indicates that the benefit of warm pre-stressing will not be eroded with irradiation.