Sodium-void reactivity in LMFBRs: a physics assessment

An extensive recalculation of sodium-void measurements from the US critical experiment program has been completed. Three-dimensional diffusion-perturbation methods and ENDF/B-Version IV data in 28 groups were used throughout this study. The results of the calculations establish the degree of confidence in the prediction of sodium-void worths in typical LMFBR environments, and further demonstrate the usefulness of a two-componet fitting process for biasing calculations in order to produce better predictions of void worths. Measurements in ninety-five zones wre analyzed, resulting in a mean C/E (calculation/experiment) ratio of 1.12 +- 0.20 before fitting, and 0.99 +- 0.09 after fitting. Bias factors for both leakage and non-leakage components were in the range 0.85 to 0.92 for a variety of design parameter variations, i.e. a number of different subsets of the data base. These results may be used to extrapolate from the critical assembly data to general LMFBR application and to estimate the uncertainty of the predicted values