Irradiation-Induced Swelling in AISI 316 Steel: Effect of Tensile and Compressive Stresses

Abstract

Effects of bending stresses on the swelling behavior of 20% cold worked AISI 316 steel were studied in material irradiated to moderately high fluences in EBR-II. Specimens used in this investigation consisted of beams subjected to four-point bending during irradiation. Fluences as high as 1.5 × 1023 n/cm2 (E > 0.1MeV) were accumulated at temperatures ranging from 412 to 458°C. The beams were subsequently sectioned to isolate regions of tensile, compressive, and neutral loading for examination by transmission electron microscopy. A complete characterization of swelling in each of the three regions was conducted to assess the influence of these stress states on the magnitude of swelling. A detailed microstructural evaluation of the material was also made to attempt to relate swelling differences with physical changes in the alloy. The results of this investigation confirm earlier experimental data that showed swelling in AISI 316 steel to be enhanced by the application of stress during irradiation and that the magnitude of swelling is independent of the sign of the applied stress. The results also show that increases in swelling can be correlated with either more or larger voids depending upon the total strain incurred. This suggests that the mechanism for stress-enhanced swelling in this alloy may be a sensitive function of the magnitude of the applied stress.