Nuclear reactor container

In a natural cooling type nuclear reactor container in which a fuel pool is disposed above the top slab in the upper portion of a dry well, there is disposed a connection cylinder for connecting a flange of a pressure vessel removed with a lid and the inner circumference of the top slab to form a reactor well upon fuel rod exchange or inspection. With such a constitution, upon fuel rod exchange or inspection, the lid of the pressure container is removed at first and water is filled into the pressure container passing through the connection cylinder connected to the flange of the lid, to form a reactor well and fuel rod exchange and inspection can be conducted by way of the well. Accordingly, since the amount of water filled in the well can be reduced, the time required for charging and discharging water can be reduced, thereby enabling to conduct operation efficiently. (T.M.)