New material for ＂nuclear fuel cladding tube＂
The ADS accelerator is recognized by the world's scientific community as the most potential tool for solving a large amount of radioactive waste and reducing the risk of deep storage. The accelerator used in it has high requirements on the flow strength, especially the stability of the accelerator. However, the current research for the application of nuclear fuel cladding tubes is still relatively weak. Decreasing material strength, decreasing thermal conductivity, poor sealing, and short service life are the most critical scientific issues in this field.
Around this problem, with the support of the National Natural Science Foundation's major research project "Fuel Multiplication and Evolution of Advanced Nuclear Fission Energy", a research team led by the Huang Qing research group of the Chinese Academy of Sciences aimed at nuclear continuous silicon carbide fibers and intermediate layer coatings. , Composite material preparation and processing technology, radiation damage and performance prediction have carried out systematic research and achieved a series of representative results.
Huang Qing introduced that the research team obtained low-oxygen content silicon carbide fibers through molecular regulation, and for the first time proposed that high-aluminum (higher than 1wt%) silicon carbide fibers containing Al-C chemical bond structure are expected to form nuclear special fiber materials with independent intellectual property rights. At the same time, it has broken through the preparation technology of liquid hyperbranched polycarbosilane (LHBPCS), and its ceramicized product is close to the SiC stoichiometry and has a low oxygen content (~ 0.1%).
On the other hand, the traditional intermediate layer interface has encountered great challenges in the application of nuclear energy structural materials. The most critical scientific problem is that the interface layer between the fiber and the matrix is swollen and mismatched under irradiation, resulting in cracks and recombination. The failure of the material's fault tolerance is the root cause of the reduced strength, reduced thermal conductivity, accelerated corrosion, and fission gas overflow of silicon carbide fiber-reinforced silicon carbide composites after irradiation.
In order to solve this problem, the research team and Peking University Xue Jianming and Wang Yugang and other research groups systematically developed the radiation damage mechanism and defect structure evolution behavior of the ternary layered MAX phase, and proposed and realized the ternary layered MAX phase for the first time. The material is used as the SiCf / SiC interlayer, and heavy ion irradiation studies show that the new interlayer has good anti-swelling properties.
One of the major challenges in the engineering application of ADS nuclear fuel ceramic cladding tubes is the problem of end sealing of silicon carbide composites. The research team used the Ti-Si-C ternary phase diagram to control the phase gradient distribution of the connecting layer to obtain high strength, low interfacial stress, and resistance. The reliable connection of radiation and corrosion resistance realized the connection of TiC / Ti3SiC2 full carbide gradient connection layer with SiC, which effectively solved the interface thermal stress problem, and the four-point bending strength of the obtained connection structure was as high as 325 MPa. In addition, the team for the first time in the world proposed a silicon carbide ceramic seamless connection solution, and developed a series of "sacrifice" type ceramic solder to achieve integrated sealing of silicon carbide ceramics and composite materials.
With the continuous advancement of research and its cross-disciplinary integration with organic chemistry, inorganic chemistry, high temperature molten salt chemistry, vacuum coating, and material calculation, the research team has continuously made a series of breakthroughs. This research direction has also been selected as the "Major Scientific Issues and Engineering Technological Difficulties" of the China Association for Science and Technology in 2018, and has been approved by the National Development and Reform Commission "Thirteenth Five-Year" Science and Education Infrastructure Platform Project "New Energy Technology and Materials Comprehensive R & D Platform-Silicon Carbide Fiber And composite materials development and application platform. "
In the opinion of researchers, the above series of research results are expected to promote the selection and practical application of nuclear fuel cladding tubes.