Experiments of Self-wastage Phenomena Elucidation in Steam Generator Tube of Sodium-cooled Fast Reactor

Abstract

The sodium–water reaction caused by failure of the steam generator tube of sodium-cooled fast reactors causes the wastage phenomenon, which is erosive and corrosive. Self-wastage takes place in the early stage of the sodium–water reaction event when a very small amount of water/steam penetrates a microcrack. When self-wastage proceeds to the inside wall of the tube, the failed area and water leakage rate will increase, whereby the area affected by the sodium–water reaction will be likely to extend. Thus, it is very important to clarify the self-wastage behavior for a locally affected region and detect water leakage in actual nuclear power plants. In this study, the authors performed self-wastage experiments under a high sodium temperature condition to evaluate the effects of the wastage form/geometry using two types of initial defect, i.e., the microfine pinhole and fatigue crack, and of the water leakage rate on the self-wastage rate. Taking into consideration the influence of crack type, we confirmed that the self-wastage rate did not strongly depend on the initial defect geometry. As a mechanism of the self-plug phenomenon, it is speculated that sodium oxide blocks and inhibits the progress of self-wastage. The dependence of the self-wastage rate on the initial sodium temperature was clearly observed, and a new self-wastage correlation was derived considering the initial sodium temperature.