Nuclear Analysis of Integral Experiments on a Li₂O Test Assembly with Local Heterogeneities Utilizing a 14-MeV Neutron Source

The integral experiments and postanalyses performed in Phase IIC of the U.S. Department of Energy (U.S. DOE)/Japan Atomic Energy Research Institute (JAERI) collaborative program on fusion neutronics focused on test blankets that include the actual heterogeneities found in several blanket designs. In one arrangement, multi-layers of Li₂O and beryllium were placed in an edge-on, horizontally alternating configuration, and in the second arrangement, vertical water coolant channels were deployed. The main objective has been to examine the accuracy of predicting key parameters such as tritium production rate (TPR), in-system spectrum, and other reaction rates around these heterogeneities and to experimentally verify the enhancement in TPR by beryllium in the first experiment. The prediction accuracy was examined in terms of calculated-to-experimental values (c/e)_i of the neutronics parameters at several spatial locations. Average local (c/e)_i values were statistically calculated for TPR from Li-6 (T₆) and from Li-7 (T₇) in addition to quantifying the prediction uncertainties in the line-integrated TPR. A relationship was developed between the prediction uncertainty in the integrated TPR and the corresponding values in the total breeding zone. This relationship enabled us to identify which subzone contributes the most to the prediction uncertainty in the overall integrated TPR.