Radial Resonance Captures in 238U Metal Rods and Spatial Resonance Production of 239Pu in Uranium-Oxide Fuels

Abstract

Precise calculation of radial distribution of resonance region capture in {sup 238}U metal rods and for partially enriched uranium-oxide fuels is important for current and proposed water-moderated power reactors. Advanced core designs for pressurized and boiling water reactors have considered resonance region in-core generation of {sup 239}Pu as a means of extending core operating cycles between refuelings. The calculations of detailed spatial resonance captures are beyond the scope of multigroup codes used for practical reactor core design because of the broad resonance energy groups required. Group average resonance capture cross-section parameters employed may conserve total neutron captures, but the spatial detail is washed out. A simplified method is presented that enables direct calculation of resonance region spatial captures in fuel moderator lattices. The validity of the method is confirmed by comparison with published experimental measurements for epicadmium capture with radial distance from the moderator-fuel interface for metal uranium rods from 0.8 to 5.0 cm in diameter. A method is illustrated for spatial resonance capture in partially enriched uranium-oxide fuel rods, and the spatial complexity of {sup 239}Pu production during conversion of {sup 238}U in the resonance region is discussed. Although the products of the conversion chain can be precisely definedmore » geometrically with operating time, their spatial concentrations cannot be calculated with the accuracy required to determine net production of {sup 239}Pu.« less