Beltline welding seam and base metal investigations of a WWER-440/230 reactor pressure vessel from the former Greifswald NPP

Nuclear plants operators must demonstrate that the structural integrity of the nuclear reactor pressure vessel (RPV) is assured during routine operations or under postulated accident conditions. Russian type WWER reactors are operated in Russia and many other European countries like Ukraine, Finland, Czech Republic and Hungary. Surveillance specimens programmes for inspection of aging of the RPV materials were implemented for the second generation (213) of WWER-440 reactors.
The paper presents results of the circumferential core weld SN0.1.4 and the base metal ring 0.3.1 of the RPV from the unit 1 of the Greifswald WWER-440/230. The investigated trepans represent the irradiated-annealed-re-irradiated (IAI) condition. The working program is focussed on the characterisation of the RPV steels through the RPV wall. The key part of the testing is aimed at the determination of the reference temperature T0 following the ASTM Test Standard E1921-05 to determine the fracture toughness in different thickness locations. It is shown that the Master Curve approach as adopted in ASTM E1921 is applicable to the investigated original WWER-440 weld and base metal.
The evaluated T0 varies through the thickness of the welding seam. The lowest T0 value was measured in the root region of the welding seam representing a uniform fine grain ferritic structure. The highest T0 of the weld seam was not measured at the inner wall surface. This is important for the assessment of ductile-to-brittle temperatures measured on sub size Charpy specimens made of weld metal compact samples removed from the inner RPV wall. Our findings imply that these samples may not represent the most conservative condition. The Charpy transition temperature TT41J estimated with results of sub size specimens after the recovery annealing was confirmed by the testing of standard Charpy V-notch specimens. The evaluated transition temperature of 51°C is close to the estimated critical embitterment temperature for the initial condition TK0 of the welding seam SN0.1.4.
The T0 from the trepan 1-4 of base metal ring 0.3.1 varies through the thickness of the welding seam. T0 decreases from -124°C at the inner surface to -90°C at a distance of 33 mm from it and again to -113°C at the outer RPV wall. The KJc values generally follow the course of the MC, although the scatter is large. The re-embrittlement during 2 campaigns operation can be assumed to be low. Hence, the variation of T0 measured through the thickness of the base metal ring 0.3.1 results basically from differences in the structure. With metallographic characterization the scatter of the MC will be investigated.
The Charpy transition temperature TT41J estimated with results of sub size specimens after the recovery annealing was confirmed by the testing of standard Charpy V-notch specimens.