Detection of Failed Coated Particles in HTGR Fuels by Acid Leaching

By acid leaching of several kinds of irradiated coated particle fuels, uranium- and 137Cs-leaching fractions were measured. These fractions were compared with the surface failure fraction of the coated particles by a visual inspection in the post-irradiation examination. From the measurements it was found that 137Cs was unsuitable as the objective nuclide for acid leaching, because this nuclide escaped from failed coated particles during irradiation or trapped in the graphite grains of the fuel-compact matrix, and therefore, it was difficult to relate the leaching fraction of 137Cs to the failure fraction of the coated particles. Cesium-137 leaching fraction was less than 10% of the uranium fraction. The uranium leaching fraction agreed fairly well with the surface failure fraction. Therefore, uranium is regarded as the suitable objective nuclide for acid leaching. Also, combination of the acid leaching and the surface inspection is an useful method for detection of failed coated particles.