Fracture mechanics characterisation of the WWER-440 reactor pressure vessel beltline welding seam of Greifswald unit 8

WWER-400 second generation (V-213) reactor pressure vessels (RPV) were produced by IZHORA in Russia by and SKODA the former Czechoslovakia. The surveillance Charpy-V and SE(B) specimens of both producers have different orientation. The main difference is the crack extension direction which is through the RPV thickness and circumferential for ISHORA and SKODA RPV, respectively. In particular for the investigation of weld metal from multilayer submerged welding seams is the crack extension direction of importance. Depending on the crack extension direction in the specimen there are different welding beads or a uniform structure along the crack front. This is especially important for the fracture toughness determined according to the Master Curve (MC) approach as standardised in the ASTM Standard Test Method E1921-05. This approach was applied on weld metal of the RPV beltline welding seam of Greifswald Unit 8 RPV. Charpy size SE(B) specimens from 13 locations equally spaced over the thickness of the welding seam were tested. The specimens are TL and TS orientation.
The fracture toughness values measured on the SE(B) specimens with both orientations follow the course of the MC. Nearly all values lie within the fracture toughness curves for 5% and 95% fracture probability. There is a strong variation of the reference temperature T0 though the thickness of the welding seam, which can be explained with structural differences. The scatter is more pronounced for the TS SE(B) specimens. It can be shown that specimens with TL and TS orientation in the welding seam have a differentiating and integrating behaviour, respectively. The statistical assumptions behind the MC approach are valid for both specimen orientation even if the structure is not uniform along the crack front.