Closure element for limiting the convection currents in an annular space about a nuclear reactor component

Closure apparatus to limit convection currents in an annular space (18) about a component (1) of a nuclear reactor cooled by a liquid metal, having a vessel closed by a very thick horizontal plate in which vertical cylindrical passages are provided for the passage of removable components disposed vertically in the reactor and resting on the plate, each of the components having between its outer surface and the inner surface of the passage an annular space (18) of a certain width in which is positioned the closure apparatus of the type having an annular cup (5) solid with the component (1) and surrounding its outer wall and containing a liquid into which a sleeve (16) dips so as to ensure closure of the annular space (18) about the component (1) characterised by the fact that it also has:

• a frusto-conical support surface (9) having as axis the vertical axis common to the component and the passage fixed at the perimeter of its large base at the passage and having its small base disposed at a lower level than the level of the large base, of a diameter greater than the external diameter of the cup (5),
• and a closure element (14) with rotational symmetry, not connected to the cup (5) and the support surface (9), having an upper part (15) intended to come to rest on the support surface (9) so as to totally close the annular space (18) at the top when the component is put in position in the reactor, the cup (5) being then below the support surface (9) and a part directed downwards constituted by the sleeve (16) resting in the cup (5) when the component (1) is handled and ensuring closure of the annular space (18) at the bottom, when the reactor is in service, the cup (5) then filling up with liquid metal.