Coated particles embedded in graphitic elements are the fuel for the High-Temperature Reactor (HTR). Experimental investigations of the performance of particles at extremely high temperatures have been conducted to achieve an understanding of coating failure mechanisms and to establish the data base for safety and risk analyses of hypothetical accidents in large-and medium-sized HTRs. The primary mechanism for coating failure and fission product release in the 1900 to 2500°C temperature range is thermal decomposition of silicon carbide (SiC). Heating tests have provided the activation energy of this process and the correlation of SiC decomposition with coating failure and subsequent fission product release. The process of fission product release proceeds in several stages. A certain amount of SiC removal at high temperatures leads to SiC deterioration, which renders a fraction of particles permeable to cesium and strontium. During 50°C/h ramped heating tests, the cesium release approaches 100% at 2500°C. With the onset of SiC failure, the release process of xenon, krypton, and iodine via diffusion through the pyrocarbon (PyC) is initiated. Under all heating conditions examined, krypton release is significantly delayed relative to cesium release due to the higher diffusivity of cesium in PyC. In the intermediate temperature range of 1600 to 1700°C (the maximum temperature in small, modular HTRs), SiC decomposition rates are negligible, and coated particle fuels retain all safety-relevant fission products.