Improving the impermeability of nuclear graphite towards molten lead-bismuth eutectic in lead-cooled fast reactor by precursor impregnation and pyrolysis processes

The permeation of molten lead-bismuth eutectic (LBE) in graphite coolant channel material is a big issue that influences the stable operation of lead-cooled fast reactor (LFR). In this study, a modification process is conducted on a commercial nuclear graphite to improve its impermeability to molten LBE used in LFR by impregnation and pyrolysis with polycarbosilane solution. Mercury and static molten LBE infiltration experiments are performed on pristine graphite and modified graphite to investigate and compare their differences in structural compactness and infiltration resistance to molten LBE. The experimental results demonstrate that the modification process can significantly improve the structural compactness of graphite substrate and thereby effectively enhance its infiltration resistance to molten LBE. Particularly, the infiltration amount of molten LBE into modified graphite is much less than that into pristine graphite under all infiltration pressures. Additionally, the dense SiC coating derived from polycarbosilane shows robust durability to stand up to the test of molten LBE infiltration experiments. These results preliminarily demonstrate that the modification process employed in this work is a feasible method to obtain graphite coolant channel material amenable to LFR.