Reactor vessel of LMFBR type reactor

Purpose: To contribute to the improvement in the safety, and improvement in the plant efficiency and working efficiency by reducing the thermal stresses generated onto the reactor vessel wall, particularly, on the side walls near the liquid level of coolants upon startup and shutdown of a nuclear reactor with a simple structure. Constitution: Heat transfer mediums are disposed to the side wall of a reactor container main body while situating the upper end thereof above the liquid level and situating the lower end thereof below the liquid level of coolants, and thermal transfer between the side wall situated above and below the liquid level and between the coolants near the liquid surface are positively carried out by the heat transferring mediums, whereby the temperature gradient in the container walls, particularly, at the liquid level can be moderated to decrease the thermal stresses applied to the reactor container walls upon startup and shutdown of the reactor while using no complicated structure or control system to thereby contribute to the improvement in the safety and in the working efficiency. (Yoshihara, H.)