An Investigation of Sintering Distortion in Full-Size Pyrochlore Rich Titanate Wasteform Pellets Due to Rapid Heating to 1350℃ in Air

摘要

Full-size (φ65mm x 25mm thick) pyrochlore rich titanate ceramic pellets designed to immobilise PuO_2 and UO_2 were sintered in air at 1350℃ for 4 hours. CeO_2 was substituted for UO_ and PuO_2 in this work. Heating rates between 2 and 15℃/min were used to determine the effect of heating rate on the integrity of the sintered pellet. Distortion of pellets was observed when heating rates in excess of 5℃/min were used. Ultra-violet dye penetrant tests revealed high levels of porosity in the more rapidly heated pellets. Finite element analysis modelling indicated that use of rapid heating rates (10 ― 15℃/min), set up thermal gradients between the surface and centre of the pellet, this in turn introduced compressive stresses at the surface and tensile stresses at the core of the pellet. These tensile stresses were the most probable cause of elliptical cracks/pores formed in the centres in these rapidly heated pellets. The FEA results were supported by evidence from the dilatometer, which showed that rapidly heated pellets did not appear to expand as much during heating in the nominal 350℃ ― 1350℃ range as pellets heated slowly.