Thermal Stress And Fatigue Analysis Of The Tubesheet Of Steam Generator In High Temperature Gas-cooled Reactor

When high temperature gas-cooled reactor restarts in short time after hot shutdown, the reactor could rise the power quickly and save much time. However, when the reactor restarts, the temperature of steam generator remains high and there is a large temperature difference between the tubesheet and the water of the secondary loop, which will generate high thermal stress and lead to fatigue damage at the weld joint of the tube and tubesheet. To ensure the safety of the tubesheet, it is necessary to study this thermal stress and fatigue damage.This paper firstly introduces the principle and structure of the steam generator, and analyzes its temperature field after shutdown by establishing its finite element model. Then the paper focuses on the condition that the reactor restarts at one hour after shutdown, establishes the finite element model of the tubesheet in steam header, and analyzes the temperature field, thermal stress and fatigue damage of the tubesheet according to ASME Codes. The temperature of the components in steam generator decreases slowly after shutdown. When the reactor restarts at one hour after shutdown the temperature of the tubesheet in steam header and the components in steam generator remain close to the normal condition.While the reactor restarts, the tube temperature decreases to the water temperature rapidly (105℃) and the temperature of the tubesheet in steam header remains high (570℃), which causes high temperature gradient and thermal stress at the weld joint of the tube and tubesheet. The thermal stress concentrates at the weld joint and in other areas the stress value is low. The thermal stress reaches a maximum value at 3 minutes after hot start and then begins to decrease. After 6 hours the reactor will run under the normal condition.Considering the interaction between creep and fatigue, the paper analyzes the fatigue damage of the tubesheet according to ASME Codes. The result of fatigue analysis shows that in the whole lifetime of the reactor (300000 hours) the number of hot start can not be more than 20.