PCI resistant fuel and method and apparatus for controlling reactivity in a reactor core

This patent describes a nuclear reactor core comprising a plurality of generally cylindrical fuel rods, each of the fuel rods comprising a cladding containing a plurality of nuclear fuel pellets stacked end-to-end within the cladding. Each fuel is coated with a layer of a refractory material interposed between the fuel pellet and the cladding of sufficient thickness to effectively prevent direct contact between the pellet and the cladding, the layer comprising a burnable poison having a non-naturally occurring tailored isotopic composition adjusted to reduce, in a controlled fashion, initial excess reactivity in the reactor core