The Effect of Coating Parameters and Annealing on the Crushing Strength of TRISO Coated Particles

The crushing strength (load at fracture) of coated particles was measured by compression between soft metal anvils. The method requires no sample preparation and can be used as a quality control method as well as a valuable tool for comparing different coating conditions during the manufacture of TRISO particles. Batches of coated particles manufactured with different coating parameters were prepared and tested. Batches prepared under different conditions exhibited significant differences in crushing strength. Higher argon concentrations in the coater gas mixture resulted in higher crushing strength. Anomalies in the crushing strength of particles are related to defects and possibly residual stresses produced during coating. The influence of annealing at 1950°C on crushing strength was also investigated. The average crushing strength of batches of particles decreased with annealing. Different preparation methods showed a marked difference in the level of deterioration of the particles with annealing. Batches produced with 80% argon gas mixture at 1300°C showed the greatest reduction in crushing strength. An inverse correlation was found between the crushing strength and the uranium that is leached from batches. The particles with the lowest crushing strength would also be more susceptible to mechanical damage during handling and consequently also to leaching of the uranium during leach tests.