Improvements to the Theory of Resonance Escape in Heterogeneous Fuel III. Spatial Depression of the Resonance Flux

In resonance capture calculations, it is usual to assume that the capture in any one resonance is unaffected by the existence of other resonances: this is known as the “flux recovery” assumption. This assumption is exact for hydrogenous moderation in a homogeneous situation. However, in highly heterogeneous lattice cells such as that of the Steam Generating Heavy Water Reactor (SGHW), in which the fuel is intimately associated with a powerful moderator, the resonance flux in the fuel is depressed below that in the bulk moderator. In this paper, this flux depression effect is investigated by using a model in which all moderation is hydrogenous and the resonances are square. This model suggests that the flux recovery assumption will overestimate ²³⁸U capture in a typical SGHW Lattice by about 5%.