[en] Object: To remove clads contained in reactor water in a light water nuclear reactor by separating it with centrifugal and nozzle actions. Structure: Reactor water in a nuclear reactor is led to a tube winding structure to provide the water with a continuous rotational motion so as to produce a gradient of the impure substance concentration in the reactor water by a centrifugal effect exerted in the radial direction of the tube winding. With the centrifugal effect accompanying the rotational motion of the reactor water within the torus, the clad in the reactor water is moved to the outer side of the torus to produce a gradient of the impure substance concentration. The afore-mentioned tube winding is provided on the inner side (in the direction of the axis of winding) with a number of small holes or gaps, through which reactor water of low impure substance concentration is taken out. In this way, the resistance in the path of the reactor water is converted to centrifugal and nozzle actions to effect separation of the reactor water and clad. (Moriyama, K.)