Wastage and overheating effects - code development supported by experimental results

Supporting the assessment of the SNR-300 steam generator accident philosophy estimations had to be made about the distribution of wastage rates to be expected and also about the time needed to produce tube ruptures by overheating. A wastage code (PROFET) has been developed on the basis of wastage tests all over the world, able to calculated wastage rate distribution on neighbouring tubes. The PROFET-code gives also the time needed to get a secondary leak taking into account self-enlargement of the primary leak, temperatures, materials, distances, angles of impact, etc., and it gives also the size of secondary leaks. Sodium-water reaction tests in the intermediate leak range simulating steam generator conditions as close as possible have shown that beyond a certain leak rate (about 80 g/s) failure of tubes in free bundle geometry by so-called overheating becomes more and more dominant (compared to wastage). 1D, 2D and 3D-calculations have been performed with ABAQUS to obtain in the time-dependent temperature distribution in tube walls located in sodium water reaction zones. These temperatures then are the basis for a stress analysis. To get data of the material properties of 2 1/4Cr in the high temperature region (600 - 1200 deg. C) special investigations like tensile tests, tube rupture tests etc. have been carried out. The main results are also presented. (author). 2 refs, 10 figs