Results of Tests to Demonstrate a 6-in.-Diameter Coater for Production of TRISO-Coated Particles for Advanced Gas Reactor Experiments

The next generation nuclear plant (NGNP)/advanced gas reactor (AGR) fuel development and qualification program includes a series of irradiation experiments in Idaho National Laboratory’s advanced test reactor. Tristructural isotropic (TRISO)-coated particles for the first AGR experiment, AGR-1, were produced at Oak Ridge National Laboratory (ORNL) in a 2-in.(5-cm)-diameter coater. A requirement of the NGNP/AGR program is to produce coated particles for later experiments in coaters more representative of industrial scale. Toward this end, tests have been performed by Babcock and Wilcox (Lynchburg, VA) in a 6-in.(15-cm)-diameter coater. These tests have led to successful fabrication of particles for the second AGR experiment, AGR-2. While a thorough study of how coating parameters affect particle properties was not the goal of these tests, the test data obtained provide insight into process parameter/coated particle property relationships. Most relationships for the 6-in.-diameter coater followed trends found with the ORNL 2-in. coater, in spite of differences in coater design and bed hydrodynamics. For example, the key coating parameters affecting pyrocarbon anisotropy were coater temperature, coating gas fraction, total gas flow rate, and kernel charge size. Anisotropy of the outer pyrolytic carbon layer also strongly correlates with coater differential pressure. In an effort to reduce the total particle fabrication run time, silicon carbide (SiC) was deposited with methyltrichlorosilane (MTS) concentrations up to $3mol%$⁠. Using only hydrogen as the fluidizing gas, the high concentration MTS tests resulted in particles with lower than desired SiC densities. However, when hydrogen was partially replaced with argon, high SiC densities were achieved with the high MTS gas fraction.