Approximate calculations for the reactivity effects of voids in nuclear reactors

Approximate methods are derived that enable the effects of certain kinds of void regions in nuclear reactors to be adequately modeled at greatly reduced costs. This reduction in costs is accomplished by: (a) specifying void boundary conditions so as to reduce the problem to a simple albedo type; (b) reducing the number of spatial dimensions; and (c) using diffusion theory, where possible, rather than transport theory or Monte Carlo methods