Patent Number: 046559906
Section: claims

1. In a light water nuclear reactor incorporating guide tubes for the fuel assemblies of said nuclear reactors, said assemblies being immersed in operation in the cooling water of the core of such a reactor, the guide tubes being of the type made from zircaloy and fixed at their two ends respectively to an upper end part and a lower end part made from stainless steel or Inconel and which incorporate devices for braking the fall of the control rods which they house during the rapid shutdown of the reactor, the improvement wherein said braking devices comprise means for restricting the diameter of the guide tubes comprising for each guide tube a zircaloy inner sleeve spot welded to the said guide tube and whose internal diameter permits the passage, with a calibrated clearance, of the corresponding control rod, the sleeve being distributed over an area of the lower portion of each guide tube, representing approximately 1/7 of its height and associated with orifices in the actual guide tubes to produce the progressive hydraulic absorption of the end of the fall of the control rods and wherein each guide tube of the fuel assembly is fixed to the upper end part by means of a conical end bore in which it is axially locked by means of a stainless steel plug fixed in the end part. 2. In a light water nuclear reactor incorporating guide tubes for the fuel assemblies of said nuclear reactors, said assemblies being immersed in operation in the cooling water of the core of such a reactor, the guide tubes being of the type made from zircaloy and fixed at their two ends respectively to an upper end part and a lower end part made from stainless steel or Inconel and which incorporate devices for braking the fall of the control rods which they house during the rapid shutdown of the reactor, the improvement wherein said braking devices comprise means for restricting the diameter of the guide tubes comprising for each guide tube a zircaloy inner sleeve spot welded to the said guide tube and whose internal diameter permits the passage, with a calibrated clearance, of the corresponding control rod, the sleeve being distributed over an area of the lower portion of each guide tube, representing approximately 1/7 of its height and associated with orifices in the actual guide tubes to produce the progressive hydraulic absorption of the end of the fall of the control rods and wherein each guide tube of the fuel assembly is fixed to the lower end part by means of a metal plug crimped or welded to the inner sleeve and joined to the lower end part by disassemblable mechanical means.