Characterization of SiC-SiC accident tolerant fuel cladding after stress application

In this work, SiC-SiC tubes with representative LWR (water cooled reactor) cladding dimensions were subjected to cycles of out-of-pile thermal stress followed by quenching. Samples were held at elevated temperatures and dropped into a water bath to replicate the high thermal stresses generated during reflooding. The samples were then characterized to measure changes in strength, permeability, and structure. Results were evaluated both for quenching into room temperature and boiling water. The results show that SiC-SiC composite tubes quenched from 1000 Celsius degrees in air into a boiling water bath exhibited no increase in He leak rate through the cylinder wall up to a pressure difference of 34.5 kPa compared to the as-fabricated state. SiC-SiC composite tubes quenched from 300-400 C. degrees into room temperature water showed an increase in He leak rate compared to the as-fabricated state. We attribute this to the more severe thermal gradient generated through the wall thickness due to higher heat flux characteristic of nucleate boiling compared to film boiling. A persistent vapor film forms around the samples quenched into boiling water, whereas no vapor film forms for the samples quenched into room temperature water. Another important result is that not loss in strength was noted compared to unquenched samples and that the stresses generated by the quenching were not enough to cause fiber fracture