Analysis of initiation and growth of a circumferential crack in the HDR-RPV-cylinder under pressurized thermal shock

Abstract

In order to simulate a nuclear emergency cooling situation, longterm cooling tests (pressurized thermal shocks) were carried out under normal operating conditions on the reactor pressure vessel of the HDR (hot steam reactor). Naturally occuring circumferential cracks in the cylindrical part of the RPV, previously induced during cyclic thermal shock tests, were subjected to internal pressure and thermal stresses. The aim of the test was crack initiation and a limited amount of stable crack growth. Analyses, applying fracture mechanical assessment methods, were carried out before and after the test and these checked against the experimental results. To this end, comprehensive numerical analyses, investigations into material property characteristics, non-destructive and destructive (fractographical) tests were carried out. Due to the conservative assumptions, the results of the precalculation lay on the safe side; this was intended as these results served, among other aspects, as the basis for the experimental boundary condition. The post calculation which was based on the actual crack geometry, the measured cooling medium temperature and the material properties local to the crack, was in good agreement with the experimental results. Thus a tool is now available which can be successfully applied to the assessment of cracks in reactor components.