Preparation of ultrafine-grain graphite by liquid dispersion technique for inhibiting the liquid fluoride salt infiltration

In this work, the mixtures of coke aggregates and coal tar pitch were used as starting materials to prepare ultrafine-grain graphites (UGG) by a liquid mixing method for the inhibition of molten salts in molten salt reactor (MSR). The average diameters of coke aggregates for UGG-1 and UGG-2 were respectively 10 and 5 μm. The liquid dispersion technique could effectively prevent fine particles of raw materials from being conglomerated. Microstructure, thermophysical and other properties of the obtained graphite were studied. A high-pressure reactor was constructed to evaluate the molten salt penetration in the graphite. Compared to isostatic graphite (IG-110,TOYO TANSO CO., LTD.), UGG-2 possessed excellent properties such as high bending strength of 81.0 ± 2.5 MPa, compressive strength of 133 ± 3 MPa, low porosity of 14.0 ± 0.1% and an average pore diameter of 0.52 ± 0.01 μm. The fluoride salt volume occupation of IG-110 and UGG-1 under 1.5 atm was 14.4% and 3.7%, respectively. While the volume occupations of UGG-2 under 1.5 atm was only 0.17%, and continued to be steady even up to 5 atm with the increase of 0.45%, less than the critical index proposed for MSR of 0.5%. The UGG-2 could effectively inhibit liquid fluoride salt infiltration and was a promising candidate as neutron moderator or reflector materials for MSR.