Analytical Determination of Critical Flaw Dimensions in Steam Generator Tubing

One of the actual problems of safe and reliable operation of NPP units with pressurized reactors is the development of tube plugging criterion for steam generator tubing. The basis for plugging criterion development is associated with existence of flaws with critical sizes at steam generator tubes. For effective application of this criterion the conditions of flaw instability should be analyzed and critical flaw sizes must be determined. Analytical investigation of flaws stability at steam generator tubes is carried out in this paper for semi-elliptical cracks since some of flaws at steam generator tubes for VVERs are similar to such cracks. The analytical solution of thermo-elastic problem dealing with the determination of stresses in tubes wall is presented. It makes it possible to perform linear fracture mechanics analysis with the aim to determine the conditions of crack instability. The approach to develop steam generator tube plugging criteria on the base of obtained results is presented and discussed.