Application of the Master Curve approach on WWER-440 reactor pressure vessel steel of the nuclear power plant Greifswald unit 8


Application of the Master Curve approach on WWER-440 reactor pressure vessel steel of the nuclear power plant Greifswald unit 8

Viehrig, H.-W.; Wallin, K.; Murasov, M.

The Master Curve (MC) approach of defining reference transition temperature, T0, has been standardized in ASTM Standard Test Method E 1921. This approach has been gaining acceptance in the codes for reactor pressure vessel (RPV) integrity assessment throughout the world. T0 is calculated from a data set of J-integral based fracture toughness values measured in the lower ductile-to-brittle transition region. This direct measurement approach is preferred over the correlative and indirect methods used in the past to assess irradiated RPV integrity. The basic MC approach for analysis of fracture test results is intended for macroscopically homogeneous steels with a body centred (ferritic) structure only. In reality, the steels in question are seldom fully macroscopically homogeneous.
The fracture toughness values measured on Charpy size SE(B) specimens of base metal from the Greifswald Unit 8 RPV show a large scatter. The basic MC evaluation following ASTM E1921 supplies a MC with many fracture toughness values which lie below the 1% fracture probability line. Thus, some inhomogeneity may still exist in the data set. In this paper, new comparatively simple extensions of the MC are applied on these fracture toughness data. The structural integrity assessment procedure SINTAP contains a lower tail modification of the MC analysis. A random estimation method describes the fracture toughness distribution following a Gaussian distribution with infinite quality steps oscillating around a normal distribution. With the application of the SINTAP modification and the random estimation higher reference temperatures were estimated in comparison to the basic MC approach according to ASTM E1921.

Keywords: cleavage fracture toughness; Master Curve approach; reactor pressure vessel steel; maximum likelihood; reference temperature

  • Lecture (Conference)
    The 4th International Conference “Safety Assurance of Nuclear Power Plants with WWER”, 22.05.2005, Podolsk, Russia

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