Abstract: A nuclear reactor having a core catcher comprising a group of upright assemblies disposed side-by-side beneath the reactor core. The assemblies each comprise a stack of spaced sacrificial plates mounted on a graphite column which collectively support the core. The plates are profiled to form vertical elongate cavities in which molten core debris can collect and solidify by heat conduction to the plates. The heat capacity of the core catcher is enhanced by cooling coils in the columns and by melting of the sacrificial plates which improves the heat conductivity of the debris.