Nonpropagating Cracks of Carburized Materials Caused by Thermal Striping in Sodium

In order to investigate crack growth characteristics due to thermal striping in liquid sodium coolant used for fast breeder reactors (FBRs), thermal striping tests in sodium have been conducted using Type 304 stainless steel and material produced by plasma carburizing Type 3o4 stainless steel. The results showed that the threshold stress intensity factor range, derived from a thermal stress analysis under the condi-tion of plane stress, could be used to predict the final lengths of the nonpropagating cracks. The depths of nonpropagating cracks increased with increasing carbon content. This tendency was attributed to the difference of the stress intensity factor range, caused by the difference in Young's moduli of the materials.