Abstract: In a nuclear reactor including a reactor vessel and a core shroud disposed within the reactor vessel in laterally spaced relation, a seismic support includes a spacer extending between laterally opposed surfaces of the reactor vessel and the core shroud to limit lateral movement of the core shroud relative to the reactor vessel and a deformable member carried by the spacer and having a configuration to deform substantially elastically in response to impacts caused by an operating basis earthquake and substantially plastically at relatively constant load in response to impacts caused by a design basis earthquake. The deformable member can be carried at an end of the spacer adjacent the reactor vessel or between the spacer and a bearing plate, and can be formed of a material having a yield strength less than that of the spacer and/or be of reduced cross-sectional area as compared with the spacer to yield under a desired seismic load.