Survival Temperature Limit of Unirradiated Coated Fuel Particles

摘要

As a part of the study related to the hypothetical accidents of the experimental VHTR, a series of out-of-pile heating experiments has been carried out to determine the survival temperature limit of unirradiated TRISO-coated UO sub 2 particles. After heating, observations were made by X-ray radiograph, and optical microphotograph of polished cross-section. X-ray diffraction analysis were also used. When heating time is short, survival temperature limit was found to be 2500 deg C for consolidated particles and 2400 deg C for loose particles. Plot of failure fraction as a function of heating time appears to be S-shaped. SiC degradation at relatively low temperatures (2200 deg C) started with thinning, whereas at high temperatures (2500 deg C) it started with micropore formation. At an extremely high temperature, total particle failure occurred physically before severe SiC degradation. At somewhat lower temperatures, total particle failure proceeded chemically after severe SiC degradation. (Atomindex citation 17:032767)