Hesham Abdelbagi Ali Abdelbagi

Influence of grain size of different fission products

The Pebble Bed Modular Reactor is a relatively new design in nuclear power plants and could be the first successful Generation IV power plant, A key feature of the Pebble Bed Modular Reactor is the fuel used in the reactor, it called TRISO Particle, consists of a small round UO2 kernel of approximately 0.5 mm diameter. This kernel is surrounded by four layers making the final diameter of the TRISO particle approximately 0.92 mm , Three of the layers are carbon allotropes with the other one composed of SiC.

The main function of these layers is to act as diffusion barriers for the nuclides produced by the fission process. Thus, these fission products are kept within the fuel particles, even under accident conditions.

The most important coating layer in the TRISO particle is composed of polycrystalline 6H-SiC, it work like a diffusion barrier for the radioactive fission products.

But there is problem, Some fission product it release from SiC coated, like Silver 110 , so now there a lot of studies try to explain the main reason that let Ag going through SiC .

The grain boundaries diffusion, it a good theory to explain this problem.

In my work, I studied the influence of grain size of different fission products, After Annealing and Implanted by different fission products.

first sample is Sic implanted by Ag 107, Under 350 c , and after that is annealed to 1900 c for 2 hour and 10 min , this sample it investigated by XRD to determine the grain sizes using Sherre equation , and also investigated by Scanning electron microscopy (SEM) , This Sample it Shown on the SEM device , a lot of cracks and this crack it happened under high temperature , and also shown the Ag 107 on the Surface of Sample. And also compared Ag release from TRISO particles with different SiC grain size, samples containing small equiaxed grains showing a lower diffusion rate than the ones containing larger columnar grains.

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