Review of oxidant resistant coating on graphite substrate of HTR fuel element

The core components of HTR mainly consist of graphite, which is an excellent solid moderating material and structure material with good irradiation performance. However, graphite is easier to be oxidized at high temperature. It is important to improve the anti-oxidation performance of graphite substrate to enhance the safety of HTR. Anti-oxidation coating has been proved that it can effectively improve the oxidation resistance of graphite substrate. The selection of coating includes the coating materials system and the preparation techniques. In addition, attention also should be paid to the anti-oxidation mechanism. SiC based coating system is most commonly used in HTR and some other coating systems such as zirconium compounds coating, noble metal coating also can be used in nuclear. However, some coating systems are not suitable in HTR because the elements contained cannot be used in high irradiation environment. The emphasis is on the antioxidant mechanism of different coating systems. Some anti-oxidation coating techniques for graphite substrate are also reviewed in this paper, such as PC, CVD, PS and slurry. Finally, the existing problems of the oxidation resistance coating are proposed and an outlook is made for the development of the protection coating system for graphite substrate used in nuclear.