In-situ Study Of The Corrosion Effect Between The Hightemperature Molten Salt With Materials And Preliminary Exploration Of Improved Technology

With the adjustment of the energy structure,the proportion of non-fossil energy is progressively increasing.Among them,wind energy,solar energy and hydropower are influenced by numerous factors including temporal availability,resources,space use and so on.Nuclear energy has been receiving high attention due to its good economic efficiency,low cost and high utilization rate.Molten salt reactors,as one of the fourth generation advanced fission reactors,have the inherent advantages of safety,less radioactive waste,and high power density.However,it is the sole reactor type that uses high-temperature liquid molten salts（as a cooling agent and as a carrier of fuel）.It is impossible to avoid the corrosion effect of high-temperature molten salts in fabrication of reactor components（such as the reaction container,loop heat exchanger,etc.）,which directly restrains the reactor lifetimes.So this problem greatly limits the development of molten salt reactors（higher operating temperature and higher power density）in the future.The static chemical dipping method is the most common way to study the corrosion problems of high-temperature molten salts,and then further characterization of the corroded samples was carried out to speculate the corrosion mechanism during reaction process.However,due to the highly corrosive of high-temperature molten salts,it is difficult to obtain the dynamic interaction between molten salts and materials by general technical means,and therefore a lot of key information and direct evidence are missed during reaction process.With the rise of synchrotron radiation source,high-flux and high energy X-rays make it possible to in-situ investigate the high-temperature corrosion mechanism of molten salts.In order to develop corrosion resistant materials,on this basis,it is found that a single material is difficult to solve the corrosion problem for high-temperature molten salts,so we also conducted a preliminary exploration of bimetallic composites.In order to better investigate the interaction between high-temperature molten salts and materials,two sets of in-situ devices,which can be well applied in high-temperature molten salts test,combined with the Shanghai Synchrotron Radiation Facility BL14B diffraction line station.And the offline characterization tests give a further more comprehensive analysis of the corrosion process.Moreover,to address corrosion issue,a composite material was constructed from the perspective of establishing a corrosion-resistant coating,and the high-temperature mechanical properties were further characterized.We hope to provide some ideas for the future development of molten salt reactor materials.The main research contents of this paper are summarized and listed as follows:（1）The compositions and some ingenious designs of the two sets in-situ equipment are briefly introduced by combining with different data acquisition mode in the Shanghai Synchrotron Radiation Facility BL14B diffraction line station.The experimental parameters that device can be satisfied are also given,and it is proved the successful application for the relevant equipment and supporting systems in the in-situ experiments.（2）The Inconel 617 nickel-based alloy and Li F-Na F-KF molten salts were tested at the high temperature 1000℃by using grazing incidence mode.FLi Na K dehydration,FLi Na K melting,Inconel 617 corrosion and FLi Na K solidification processes are clearly observed during in-situ corrosion studies.By calculating the changes of the lattice constants in the contact interface between the alloy and the molten salts with the corrosion time and temperature,and the corrosion morphology and the elements distribution of the alloy surface were observed by electron probe microanalysis and scanning electron microscopy（SEM）,the corrosion mechanism of the molten salts leading to alloy surface elemental segregation was analyzed.（3）High-temperature in-situ experiments were carried out between different chloride molten salts with MAX phase-Ti₃Al C₂,and the molten salts were Zn Cl₂,Cu Cl₂-KCl and Ni Cl₂-KCl eutectic salts,respectively.The in-situ miniature high-temperature rotational powder apparatus was used in these tests.Compared with different conditions in-situ experiments,the various corrosion mechanisms of chloride salts on Ti₃Al C₂ were illustrated in in-situ experiments,and the replacement reaction mechanism happened in Zn Cl₂molten salts on Ti₃Al C₂with anaerobic conditions and the mechanism of certain corrosion resistance under oxygen conditions were also discussed,respectively.The Cu Cl₂-KCl and Ni Cl₂-KCl eutectic salt was mainly formed the corresponding eutectic alloy phase in Ti₃Al C₂ layer causing the corrosion mechanism under high temperature anaerobic conditions.These results provide some reference for further studying the structure and elemental composition of anti-corrosion materials.（4）A corrosion-resisting materials for high-temperature molten salts were developed by composite hot rolling,which combines the excellent high temperature mechanical properties of Inconel 617 alloy with the great corrosion resistance of pure nickel.The good bonding and high-temperature mechanical properties of the composites were demonstrated by relevant experimental characterization,and the high-temperature precipitation particles of the alloy were further analyzed by SEM and transmission electron microscopy to elucidate the effect of high temperature mechanical strength.This provides some new ideas to develop higher temperature structural materials for commercial molten salt reactors.