A simple multiplicative model for computing azimuthal power variations in Savannah River Site reactor assemblies

Knowledge of assembly spatial power distribution is required to establish assembly effluent limits for Savannah River Site (SRS) reactors. The power distribution is determined by a number of random geometric considerations. This randomness presents some challenges when attempting to quantify the power peaking. A single, worst-case scenario is likely to be too conservative, so a probabilistic distribution function (PDF) is used to describe the power peaking. To derive a PDF from several hundred explicit calculations would be impractical because the codes capable of handling the geometry (Monte Carlo codes such as MCNP) are CPU intensive. Instead, we have derived five response functions that are sufficient to determine the peaking for any configuration and make possible a PDF based upon several billion simulations