The present invention provides a nuclear fuel assembly, where a boron-containing compound is used as a burnable poison and is distributed in a majority of the rods in the assembly. The assembly comprises a plurality of fuel rods, each fuel rod containing a plurality of nuclear fuel pellets, wherein at least one fuel pellet in more than 50% of the fuel rods in the fuel assembly comprises a sintered admixture of a metal oxide, metal carbide or metal nitride and a boron-containing compound.