BRUTE: Evaluation of Mechanical Properties of True Reactor Pressure Vessel Material From Barsebäck 2

Abstract

Project BRUTE has investigated weld materials extracted from the decommissioned Barsebäck 2 reactor pressure vessel. The materials investigated originate from the pressure vessel head (RPVH) and beltline regions. The performed mechanical testing include tensile, Charpy impact and fracture toughness testing. Tensile testing with miniature specimens demonstrates a difference of over 50 MPa in the yield and ultimate tensile strengths of the RPVH and beltline materials. Beltline specimens tested at the operating temperature exhibit discontinuity past the yield region, possibly indicating dynamic strain aging. Charpy impact tests were performed around the transition region of the material. Transition curves were fitted, and reference temperatures T28J of −85 °C and −106 °C were determined for RPVH and beltline materials, respectively. This indicates better material properties at beltline compared to the RPVH, in agreement with tensile results. The reference temperatures T28J were further utilized to estimate brittle fracture initiation toughness reference temperatures T0. Fracture toughness testing follows the Master Curve methodology defined in ASTM standard E1921. Reference temperatures T0 were determined at −115.1 °C and −101.1 °C for the RPVH and beltline, respectively, but the tests indicate inhomogeneity in both materials. The mean reference temperatures of the multimodal models TM were determined at −110.0 °C and −96.5 °C, and the associated, margin adjusted lower confidence bounds TM5%, MA at −13.3 °C and −53.0 °C for the RPVH and beltline materials, respectively. The latter values indicate that the inhomogeneity is more extensive in the RPVH. The estimates obtained from the Charpy impact toughness results do not correlate consistently with the fracture toughness-based transition temperature, possibly due to the inhomogeneity of the materials. The results show that the safety of the materials can be assessed reliably, provided that contemporary methods, equipment and analyses are used.