Reactor core consisting of a number of interconnected groups of similar columns

This patent is concerned with the construction of a reactor core with additonal play between adjacent columns of blocks with the aim of making it easy to discharge columns deformed in operation with their fuel rods. This play is provided in addition to the normal 'cold play', which acts to accommodate thermal expansion in operation, but must be compensated for in normal operating in order to prevent undesirable movement and vibration of the columns of blocks. This compensation takes place by inserting a spreader rod according to the invention. It consists of a material of low neutron capture crossection and has a diameter equal to that of the control rods, as both are inserted into identical channels (and in about the same numbers). The cylindrical rod has no particular spreading arrangement, but is tapered at the lower end or to a lesser extent over the whole length. By pulling out one (or more) spreader rods in the vicinity of a column of blocks, additional play is provided, and the column can easily be replaced and the spreader rod reinserted. The block elements or blocks laid on top of each other in columns have irregular pentagonal crossection. They contain holes (e.g. on 2 diameters 3 + 12) to accommodate fuel elements with their central cooling channels. The circular channels for spreader and control rods are formed by cut-outs at the corners of 4 adjacent, i.e. touching pentagonal blocks. By this configuration an inter-connection is created with the full complement of columns of blocks, which prevents an adjacent column moving into the gap formed when a column is removed. (RW)