Evaluation of the Risk of Damages in Mixing Zones: EDF R&D Programme

Following the incident (through-wall crack and crazing zones) of May 1998 on the principal mixing zone of the residual heat removal system at CIVAUX nuclear plant, EDF has initiated a R&D programme to understand the incident and assess the risks of damage on other nuclear plant mixing zones. The programme includes different sectors of development: assessment of temperature fluctuations in mixing zones, study of high-cycle thermal fatigue behaviour of austenitic steel and development of mechanical methodologies for damage assessment and propagation of crazing zones (thermal striping). A series of tests is being performed in support of the programme. The paper develops the description of each sector of the programme: tests performed, on-site measurements and numerical interpretations. The first results are presented.