Neutron streaming in a cylindrical annulus: a review of theory and comparison of methods

It is sometimes necessary to know what effect an empty cylindrical channel has on reactivity of a multiplying system. A number of methods that have been used in the past are reviewed and compared and their limitations pointed out by comparison with a derivation from first principles. In particular, we are able to present expressions for the linear extrapolation distance at the channel surface, thereby providing a useful boundary condition for diffusion theory calculations. The error introduced when certain simplifying assumptions are made is assessed. This paper should also be regarded as an historical survey which attempts to relate a number of seemingly disparate results to a common equation.