Nuclear reactor fuel assembly with uranium and plutonium fuel rods - enriched in uranium 235 and/or plutonium in axial direction for light water reactor

摘要

In a nuclear fuel assembly with a ducted case contg. numerous fuel rods, at least some of the fuel rods are charged with a fuel mixt. of U and Pu and u-235 enrichment and/or Pu concn. is provided in predetermined gradient in the axial direction of the fuel rods. Some of) the rods may contain a burnable poison, with axial concn. gradient. If U-Pu fuel rods and U fuel rods without burnable poison are used, the upper and lower zones of the U fuel rods, corresp. to 1/24 of the effective length of the rod, are charged with natural U and (pt. of) the rest of the rod has an enrichment zone, except the upper and lower zones sepd. by a middle zone. The enrichment of the upper and lower zones is less than that of the middle zone and the concn. of burnable poison gradually decreases from the upper to the middle and then the lower zone. Each rod charged with the U-Pu mixt, has a cavity making it max. 15 cm longer than the U rod. Some fuel rods with a total cross-sectional area more than 6% of the cross-sectional area of all the fuel rods in the ducted case are replaced together by a water rod, through which non-boiling water flows, or leave a zone free from fuel for water flow. USE/ADVANTAGES - The assembly is used in a light water reactor. The thermal region or switch-off region of the core is better and the fuel transport and handling costs are reduced.