Structural Integrity Assessment of Once-Through Steam Generator under Density Wave Oscillation Using Finite Element Analysis

In this study, a stress evaluation was performed to verify the structural integrity of the small modular reactor (SMR) steam generator (SG) tube under the loading conditions of density wave oscillation (DWO). Finite element (FE) analysis was conducted using ANSYS Workbench, and the stress evaluation was carried out in accordance with the requirements of the Korea Electric Power Industry Code (KEPIC) MNB 3221.1 and 3222.2. The SMR SG consists of a total of 17 layers composed of multiple tubes. This study analyzed only the tubes in the 1st and 17th rows. The results of the stress evaluation showed that the maximum stress ratios to the allowable stress limits were 26.4% and 14.6% for the 1st and 17th row SG tubes, respectively. The maximum difference in alternating stress intensity was less than 52.4 MPa for Cases 1 and 2 on the 1st row SG tube. According to the design fatigue curve in Figure I-9.2M of ASME Section III Appendices, it was confirmed that the alternating stresses on the SG tubes due to DWO loading cycles can be sustained indefinitely.