A support and sealing arrangement for the vessel head of a nuclear reactor. The arrangement comprises a first support ring supported in the vessel cavity in which the reactor vessel is disposed, a plurality of flexible struts spaced about the circumference of the reactor vessel each of which has one end connected to the first support ring, and a second support ring which is supported by the other ends of the flexible struts to support the vessel head. The first and second support rings are each concentrically arranged with respect to the reactor vessel. Also, sealing means are provided for preventing fluid communication between the interior of the reactor vessel and the vessel cavity, and between the vessel cavity and the outside atmosphere.