The effect of molten FLiNaK salt infiltration on the strength of graphite

Abstract Graphite has been identified as a structural and neutron-moderator material in the molten salt reactor (MSR). In order to support the structural material development for MSR, the influence of molten salt infiltration on the mechanical strength of graphite was studied. The high-temperature mechanical strength of graphite grades IG-110 and NG-CT-10 decrease with the increasing of weight gain ratio during the molten FLiNaK salt infiltration. It shows a noticeable high-temperature mechanical strength degradation, which can be evidenced by the softening coefficients. The smaller softening coefficient of compressive strength compared with that of tensile strength at the same infiltration pressure indicates the compressive strength is more vulnerable to the molten salt infiltration than the tensile strength. The major fragments analysis of the samples after compressive strength tests shows that the molten FLiNaK salt infiltrated graphite samples experience are longitudinal splitting fracture rather than the shear fracture of virgin graphite. The increase of thermal strain after molten salt infiltration indicates an extra stress in infiltrated graphite, which may be one of the reasons for the failure mechanism change.