[en] A study was performed to provide a description of the release of fission products from failed fuel particles during a core heatup event in an HTGR. The need for this study was established in the Accident Initiation and Progression Analysis program. The release of fission products was measured from laser-failed BISO ThO₂, TRISO UC₂, and weak acid resin (WAR) particles over a range of burnups. The burnups were 0.25, 1.4 and 15.7% FIMA for ThO₂ particles, 23.5 and 74% FIMA for UC₂ particles, and 60% FIMA for WAR particles. The fission products measured were nuclides of xenon, iodine, krypton, tellurium, and cesium. Two types of experiments were performed: isothermal and temperature rise experiments. The range of the temperatures was from 1200⁰ to 2300⁰C. In the temperature rise experiments, the heating rates were between 50⁰ and 450⁰C/h