The Mechanical Design of TRISO-Coated Particle Fuels for the Large HTGR

Abstract

The performance of TRISO-coated carbide fissile particles, of the type to be used in the large HTGR, correlates well with statistically based calculations of stresses in the SiC coating. Three coated particle batches, containing a total of nearly 104 individual coated particles, showed insignificant coating failure (≤0.2%) after exposure to essentially the most severe combined conditions of fast neutron exposure, burnup, and temperature to be experienced by fuel in a large HTGR. This high reliability derives from the fact that less than 1% of the particles in each batch had SiC tensile stresses greater than 30 000 psi, while the SiC layer in about 80% of the coated particles in each batch remained in compression throughout life. Two additional experimental batches of TRISO-coated carbide fissile particles had thinner coatings that resulted in higher mean SiC stresses in each batch and in probabilities of SiC coating stresses greater than 30 000 psi of 3.5 and 8.5%. This compares with the observed incidenc...