Development of Duplex Specimens for Potential Application in Testing of Highly Irradiated Weld Metals

According to the German Safety Standard 3201.2 [1] of the Nuclear Safety Standards Commission (KTA) it must be proven that for cracks which may have initiated crack arrest will occur in the wall (of the RPV). This importance of crack arrest for the fracture mechanics concept requires reliable experimental data, especially regarding irradiated materials and testing techniques with appropriate specimens. The recently finished CARISMA (Crack initiation and ARrest of Irradiated Steel MAterials) [2] program shows some limitations to use Compact Crack Arrest (CCA) specimens manufactured from highly irradiated weld metals. The welding process to generate the brittle zone at the tip of the starter notch causes annealing effects which influences the heat affected zone (HAZ) of the brittle weld. These effects lead to a crack arrest in the HAZ after unstable crack initiation. During further loading the limits of the test equipment were reached, but no unstable crack initiation event occurred. The use of so-called Duplex specimens with a pre-hardened specimen part instead of using CCA specimens is a promising alternative which still needs further investigation. This type of specimen was already used successfully at the Oak Ridge National Laboratory in the “Heavy-Section Steel Irradiation” (HSSI) [4] program for two irradiated high copper welds. It should be noticed, that the Duplex specimens used in the HSSI program were first produced, and afterwards irradiated in the Oak Ridge Research Reactor. In the case presented, the material is already irradiated, so the specimens must be manufactured in that condition. This situation complicates the development of a successful crack arrest test with Duplex specimens. The objectives of the experimental study, the test matrix and the approach to find an optimized specimen design for crack arrest testing are described.