ASSESSMENT OF HIGH CYCLE THERMAL FATIGUE ACCORDING TO HOTCOLD WATER MIXED FLOW IN NUCLEAR POWER PLANT PIPING SYSTEM

In the case of nuclear power plants, there is a risk of thermal fatigue in equipment and piping affecting system soundness because the temperature change of the system accompanies in every operation and shutdown. Therefore, in order to prevent the excess of the fatigue limit during the lifetime of plants, in the designing stage, the fatigue limit of each piping material is determined. However, there are many cases where equipment or piping is locally subjected to thermal fatigue that is not considered in the design, resulting in damage to the equipment and piping, and failure of the operation. Currently, local thermal fatigue generation mechanisms that are not taken into account in nuclear power plant design are gradually being identified. In this paper, the effects of the fluid temperature fluctuations on the piping soundness due to the mixing of hot and cold water, one of the local thermal fatigue generating mechanisms, were evaluated.