Some components of the main primary circuit of PWR nuclear power plants contain nickel-base alloy 600 parts (steam generator (SG) tubes, steam generator partition plates, lower internal radial supports). It is well known that this alloy is prone to stress corrosion cracking in the primary water environment. In 2002, surface cracks were discovered for the first time in SG partition plates of EDF 900 MWe NPP. The integrity of the SG containing these cracks must be demonstrated for all operating conditions, including accidental conditions. Due to the high tensile consolidation rate and the high fracture toughness of alloy 600, this was proved using limit load analysis. However, for a thorough demonstration, an experimental program was launched at EDF/R&D to better understand the behaviour of cracks in this high fracture toughness material. Centre Cracked Tensile (CCT) specimens were selected for this experimental program, being closer to the industrial case than conventional CT specimens.

Two tests have been conducted at room temperature on large CCT specimens containing a semi-elliptical crack. The paper presents the design of the CCT tests, the material characterisation, the main results of the tests and their numerical interpretation.

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