Failure probability study of HTR graphite component using microstructure-based model

Nuclear graphite is widely used as in-core structural material in the high temperature gas-cooled reactors (HTRs). As mechanical properties of graphite change with neutron irradiation and temperature, the reliability evaluation of graphite internals of a HTR is commonly accomplished by the finite element analysis using various constitutive creep models and the following structural failure prediction with introduction of failure models that have essential impact on the final evaluation result. In this paper, a microstructure-based failure model proposed by Burchell in 1996 in conjunction with the finite element code INET-GRA3D of INET is used to study failure probability of a graphite side reflector design in the pebble-bed HTR during its entire service life from the microstructural view. The corresponding irradiation-induced creep stress analysis is carried out using both the UKAEA model and the Kennedy model. H-451 graphite is selected as material input since its irradiation material data from both macrostructure tests and microstructure observation is available. The results are compared with those using the macrostructure-based Weibull model commonly accepted in the engineering field and consistent trends are observed. Moreover, The Burchell model leads to the failure probability more sensitive to stress levels than the Weibull model.