Seismic snubber accommodating variable caps in pressure vessels

Apparatus for accommodating seismic forces comprises a plunger element which slides axially in a bore in a dashpot element secured to the internals of a steam generator, the plunger being biased against the shell of the pressure vessel by a series of Belleville springs. The plunger and dashpot element form an absorber chamber in communication with a collapsible reservoir of an incompressible fluid through a metering passageway to maintain the chamber full of fluid. The passageway is of a size that allows fluid flow at the slow rates of movement between the shell and internals associated with temperature and pressure changes, but allows essentially no fluid flow at the frequency of seismic vibrations, such that the plunger, dashpot and fluid then act as a solid element between the shell and internals. The metering passageway can be in the dashpot wall rather than the piston. (author)