A Modified Technique for Crack Formation on Nuclear Steam Generator Tubing

Abstract

For the aging management and safety assurance of an operating pressurized water reactor (PWR), the integrity of steam generator (SG) tubes receives increasing attention. Non-destructive examination by eddy current technique (ECT), leak rate measurement and burst pressure evaluation constitute key elements. SG tubes containing cracks with physical and microstructural characteristics similar to those of field-aged tubes are needed for the effort. We explored a radial dent loading method to introduce axial intergranular cracks using sensitized alloy 600 tubes in laboratories as a procedure to generate a library of laboratory degraded tubes (LDT) for ECT qualification. Based on three-dimensional finite element analysis and preliminary experimental work that the method is shown to be more useful than the internal pressurization method for the production of cracks with high aspect ratio. In addition, direct current potential drop (DCPD) method applied with array probes has been developed for use in accurate monitoring and control of crack size and shape. In order to minimize plastic deformation of region containing cracks, it is desired to use the radial dent loading only for shallow crack initiation. Then, subsequent growth of crack depth can be made by internal pressurization method.