Analysis of the Self-wastage Phenomena caused by Small Water/Steam Leaks

One of the important problems to be solved in the design and construction of a sodium cooled fast reactor is to confirm the safety and reliability of the steam generator which transfers the heat from the sodium to the water. Sodium-water reaction events may occur when material faults such as a pinhole or crack occur in the heat transfer tube wall. When such a leak occurs, it results an important phenomena, so called 'wastage' which may cause damage to or a failure of the adjacent tubes. Another type of phenomenon is a 'self-wastage' which is not wastage on a wall of the adjacent tubes, but which occurs on the inside of the leakage site itself. If a steam generator is operated for some time with this condition, it is possible to damage the leak hole itself, which may eventually enlarge into a much larger opening. There is a danger that the resultant leak rate caused by a self-wastage might create the state of a small leak, or even an intermediate leak which would then give rise to the problems of a multi-target wastage. It has been observed in this study and others that the diameter of the nozzle hole grows to become a larger size in a very short time. Therefore, it is very significant to predict these phenomena quantitatively from the view of designing a steam generator and its leak detection systems