The molten salt reactor concept is based on dissolving the fuel in a molten salt. This liquid fuel concept is highly innovative and in many respects represents a break with current reactors, which are all based on the use of a solid fuel and a fluid coolant. Recently, the emergence of American start-ups proposing this innovative concept and the major effort made in China have revived interest worldwide in studying this technology, which offers a number of advantages, both real and potential, over the use of solid fuel, particularly in terms of incineration and intrinsic safety. To build a feasibility demonstrator for this breakthrough concept, extensive research is needed to acquire data and justify the behaviour of the containment barriers, primarily the metal barrier in contact with the salt. In the case of molten salt reactors, the structural materials, nickel-based alloys, are chosen to optimise their behaviour in terms of corrosion and high temperature. Corrosion of the materials is one of the critical points to be overcome when building this reactor. A detailed understanding of the corrosion mechanisms of the alloy chosen as the structural material, on the one hand, and of the chemistry of the ternary salt NaCl-ThCl4-UCl3 envisaged, on the other hand, are necessary to predict the material corrosion rate over the lifetime of the demonstrator. These studies will enable several corrosion mitigation methods to be developed. Each of these processes will be tested and evaluated under nominal conditions and then aggravated.
The first part will be devoted to understanding the corrosion mechanisms of the alloy and the chemistry of the NaCl-ThCl4-UCl3 salt. To this end, tests will be carried out at the IPN in Orsay and the corrosion mechanisms and chemistry studies will be established using electrochemical techniques and microstructural characterisation of corroded samples (thermogravimetry, SEM, TEM, XPS, Raman, GD-OES, etc.). Secondly, material protection tests using different types of salt redox control will be carried out and then tested in nominal and aggravated environments.
This approach will make it possible to meet a major and ambitious corrosion control challenge for an innovative energy process.