Patent Number: 040010783
Section: summary

This invention relates generally to nuclear reactor systems and, more particularly, to improved control apparatus for a nuclear reactor system. Typical nuclear reactor systems employ control rods comprised of neutron adsorber material which may be inserted into or withdrawn from the reactive core of the nuclear reactor. Where the reactor core is surrounded by a pressure vessel, such as is the case in a high temperature gas-cooled reactor, the control rods typically are operated by a mechanism extending through a penetration in the pressure vessel, and indeed the control rods themselves very often may be retracted into such penetration or penetrations. In the design of a nuclear reactor system of the type described, it is desirable to minimize the number of penetrations in the pressure vessel which encloses the core to maximize the structural integrity of the pressure vessel. On the other hand, an uneven distribution of control rods throughout a region of the core or throughout the entire core can result in extreme variations in the neutron flux across a cross section of the core. This can cause undesirable variations in core temperature and in the rate at which fuel burn-up occurs in the core. Many prior art nuclear reactor systems have therefore involved a compromise between the number of pressure vessel penetrations for the control rods and the uniformity of distribution of the control rods in the reactor core. Often, this comprise is not satisfactory, since it necessarily involves a reduction in both structural integrity of the pressure vessel and in the evenness of distribution of neutron flux in the core. It is an object of the present invention to provide improved control apparatus for a nuclear reactor system. It is another object of the invention to provide control apparatus for a nuclear reactor system which allows a minimization in the number of reactor pressure vessel penetrations required without compromising the uniformity of neutron flux in the reactor core. Another object of the invention is to provide improved control apparatus for a nuclear reactor system capable of utilizing a single reactor pressure vessel penetration for control rods for a region of the core wherein control rod guide holes in the core are distributed over an area larger than the cross section of the penetration.