[en] An improved cooling system for incorporation into nuclear reactor core catchers is described. The core catcher, positioned below the nuclear reactor core in which metal-oxide nuclear fuel is assembled, is arranged to catch any molten material which may run out of the core in the event of any serious over-heating. In this design the core catcher incorporates not only cooling coils but also balls, columns or rods of carbon presenting relatively large surface areas to react with molten oxides and to convert these oxides at least partially and to a significant degree, from a cooling standpoint, into carbides. (U.K.)