This project proposed here will make use of the TRISO particles irradiated in a unique programme – PYCASSO (PYrocarbon irradiation for Creep And Swelling/Shrinkage of Objects), to study the densification kinetics of the buffer and PyC layers excluding effects due to the presence of fuel, such as pressurization or chemical attack by fission products. Most ongoing programs focus on standard TRISO particles where multiple factors could influence the dimensional changes and fission product transportation/retention; this current project aims to separate these effect thereby contributes to the fundamental mechanistic understanding of buffer and PyC dimensional changes.
Specifically, high resolution X-ray computed tomography will be adopted to capture the 3D microstructure of two types of particles (Kernel/Buffer and Kernel/Buffer/SiC) irradiated at 1000C to two doses (1.65x1025 n/cm2 and 2.05x1025 n/cm2). The thickness/radius of each layer will be subsequently derived from image segmentation. The results will be combined with the other two particles irradiated in the same program under the same conditions and have been previously characterized (Kernel/Buffer/PyC and Kernel/Buffer/PyC/SiC). This will allow us to (1) acquire first-hand information on the densification of the buffer layer after irradiation with and without PyC layer, and (2) assess the difference between unrestrained and restraint swelling of PyC and SiC. In addition, three particles of each type will be polished to reveal the cross-sections for post analysis using electron backscatter diffraction, Raman spectroscopy and transmission electron microscope to acquire information on the crystallite size/orientation of the SiC, residual stresses and irradiation damage in all layers.
The outcome of the project will provide valuable input to the understanding of irradiation induced dimensional change in TRISO particles excluding the impact of fission products and pressurization to underpin the design and optimization of TRISO fuel.