Nuclear reactor

An opening in the wall of the pressure vessel of the helium-cooled reactor is closed by means of double-closure devices. The double closure consists of a pan-shaped primary lid that may be damaged from outside and whose convex side faces the opening and locks it gas-tight. Looking into the direction of the opening, the other, secondary closure is arranged which is formed by a double pan. These two pan elements are tightly connected with one another at their edges while their convex sides also face the opening and the cavity formed between them is filled with water. It is divided into an inlet and an outlet chamber for cooling water, both chambers lying concentrically one within the other. If the primary closure is damaged, only a limited amount of helium is flowing out, the flow resistance being increased by the tightening effect of the secondary closure. (DG)