Study on Application of Probabilistic Method in ASME Standard on Fine-grained Graphite

Graphite has high neutron scattering cross section and low thermal neutron absorption cross section. Therefore, graphite is widely used in HTR as moderator, reflector and core structure material. In the design of HTR, it is important to guarantee the structural integrity of graphite components. Because of the variability of material strength, probabilistic approach is well suited for nuclear graphite. However, the probabilistic method adopted by ASME code focuses on coarse-grained graphite such as NBG-18 and its application on fine-grained graphite like IG-110 remains unknown. In the present paper, the probabilistic method of ASME was introduced and its application on fine-grained graphite was verified with different tests. The results indicate that the aforementioned method will lead to very conservative failure probability for fine-grained graphite.