A fuel bundle design for a heavy water moderated and cooled reactor and in particular, to a fuel bundle that provides control of the reactivity upon coolant voiding in a reactor such as a CANDU type nuclear reactor. The geometry of the fuel bundle reduces the coolant mean chord length. A centrally disposed neutron scattering material is surrounded by an annular region in which fuel pins are arranged. The scattering material can be amorphous carbon or reticulated silicon carbide. The fuel pins are arranged in concentric rings having equal numbers of pins with the pins in inner rings being smaller in diameter than, and nestled between adjacent pins in the adjacent outer ring.
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