Virgin and irradiated hexagonal subassembly duct crushing test and analysis

The response of hexagonal subassembly ducts in reactor operating conditions submitted to various static and dynamic loadings is of major interest for safety studies. The material properties of the cold-worked type 316 stainless steel hexcans are particularly heterogeneous because of the remaining cold working gradient between flat and corner and of the irradiation inducing embrittlement, depending on the irradiation temperature, as suggested by the substantial reductions of ductility observed in the tensile tests. Therefore, simple tests were performed on irradiated structure to look for brittle failure and for failure mode identification. Quasi-static crushing tests were undertaken on sections cut from virgin and irradiated 316 SS PHENIX hexcans. A constant vertical deflection rate across the opposite faces of the sections was applied with an INSTRON machine set up in a hot cell; the compressive loads and the loaded corner displacements were recorded at 400 and 560 deg C. On the virgin samples, at 400 and 560 deg C, crack initiations and propagations at the location of maximum stresses were observed. As far as the irradiated ducts are concerned, clean failures occurred in lateral corners. The influence of the irradiation temperature is large: the load-deflection diagrams are quite different at 400 and 560 deg C. Evidence for Young's modulus alteration by irradiation is also presented; elastic-plastic analyses have been made with the bi-dimensional finite element code INCA. Good agreement is observed between the data and the calculations, even at large deflections: this allows to predict the different collapse loads and to obtain the strain values at the collapse points and at the failure locations of the irradiated specimens