BIAXIAL TESTING FOR NUCLEAR GRADE GRAPHITE BY BALL ON THREE BALLS ASSESSMENT

Nuclear grade (high-purity) graphite for fuel element and moderator material in Advanced Gas Cooling Reactors (AGR) displays large scatter in strength and a non-linear stress-strain response from the damage accumulation. These responses can be characterized as quasi-brittle behaviour. Current assessments of fracture in core graphite components are based on the linear elastic approximation and thus represent a major assumption. The quasi-brittle behaviour gives challenge to assess the real nuclear graphite component. The selected test method would help to bridge the gap between micro-scale to macro-scale in real reactor component. The small-scale level works would contribute some statistical data to manifests the failure in real component. The evaluation and choice of different solution design of biaxial test will be discussed in this paper. The ball on-three ball test method was used for assessment test follows by numerous of analytical method. The results shown that biaxial strength of the EY9 graphite was depending on the method used for evaluation. Some analytical methods demonstrated the contradiction values of biaxial strength, therefore indicated invalid strength and could not be used to assess the mechanical properties of nuclear graphite.