Validation of Surveillance Concepts and Trend Curves by the Investigation of Decommissioned Reactor Pressure Vessels

摘要

The investigation of reactor pressure vessel (RPV) material from the decommissioned Greifswald nuclear power plant representing the first generation of Russian-type WWER-440/V-230 reactors offers the opportunity to evaluate the real toughness response. This paper presents test results measured on trepans taken from the multilayer beltline welding seam SN0.1.4 and forged base metal ring 0.3.1 located in the reactor core region of the Unit 4 RPV. This unit was shut down after 11 years of operation. The characterization of the irradiation response was based on the measurement of the hardness, the tensile strength, the master curve reference temperature, T_0, and the Charpy-V transition temperature through the thickness of multilayer beltline welding seam SN0.1.4 and the forged base metal ring 0.3.1. For the beltline welding seam we observed a large variation in the through-thickness master curve T_0 values. The T_0 values measured with the T-S-oriented Charpy size SE(B) specimens strongly depended on the intrinsic welding bead microstructure along the crack tip. The progression of the T_0 values through the thickness-forged base metal ring 0.3.1 ranged from -121 to -130°C and indicated no irradiation-induced embrittlement within the fluence range of 5.38 to 1.20 x 10~(19) n/cm~2 (E > 0.5 MeV) through the thickness of the RPV wall. More than the allowed 2 % of the specimen size-adjusted fracture toughness values, K_(JC-1T), were below the fracture toughness curve for 2 % fracture probability. The reason for the occurrence of very low K_(JC-1T) values was seen in the intergranular planes detected on the fractured surfaces of the specimens. Modified master curve-based evaluation methods indicated the material to be nonhomogeneous. This investigation shows that the measured irradiation response of the investigated RPV materials does not correspond to the forecast according to the current Russian code.