Considering brittleness of tungsten in failure analysis of helium-cooled divertor components with functionally graded tungsten/EUROFER97 joints

Helium-cooled divertor components made of tungsten and reduced activated ferritic martensitic steel are part of current research for future power plants. Two different failure analyses, a deterministic and a probabilistic, have been performed on the tungsten section of the considered thimble of the divertor component which is joined to a steel cartridge by a functionally graded tungsten/EUROFER97 layer.In the deterministic failure analysis, the extended finite element method (XFEM) is used providing insights concerning the initiation and the propagation of possible cracks, which depends on the layer thickness. Due to the brittleness of tungsten at low temperatures and its embrittlement in view of neutron irradiation a probabilistic failure analysis is necessary to assess the reliability of the divertor component. Failure probabilities for the tungsten thimble were calculated based on Weibull statistics using the STAU code. The influence of the thickness and inclination angle of functionally graded tungsten/EUROFER97 joints on the failure probabilities were studied and revealed a minimum required layer thickness of 3000 μm and the necessity of an inclination. The Weibull parameters for a tungsten alloy with 1 wt.% La2O3 were determined in four point bending tests and used as input data for the failure analysis of the component during production.

► Functionally graded joints between W and FeCr were assessed by FE calculations.
► XFEM-simulation of crack initiation and propagation in W.
► Necessary design aspects of the joint identified by probabilistic failure analysis.
► Weibull parameters for WLa2O3 were determined in four point bending tests.