Spectral Fine-Structure Effects in the Reactivity-Reaction-Rate Method for Determining Capture-to-Fission Ratios

Effects of fine-structure fluctuations in the importance function spectrum on the accuracy of the reactivity-reaction-rate (RRR) method for the determination of the effective capture-to-fission ratio () are investigated using a simple single-resonance model. It is found that multigroup calculations with flux-averaged group constants do not adequately take these effects into account. This can impair the accuracy of the value of determined by the RRR method. A prescription for accurately taking the fine-structure spectral effects into account is given.