Comparative Analysis For Phase IIA and IIB Experiments of the U.S./JAERI Collaborative Program on Fusion Blanket Neutronics

Several fusion-oriented integral experiments were performed in Phase II of the U.S./JAERI Collaborative Program on Fusion Neutronics where the geometrical configurations and source condition closely simulate the incident spectrum in fusion reactors. The main objective of the program is to estimate the uncertainties involved in predicting tritium breeding rate in Li₂O and other neutronics parameters in fusion blankets that include engineering features (i.e., first wall, multiplier). In Phase II, the Li₂O test assembly is placed on one end of a Li₂CO₃ enclosure that houses the D-T neutron source. Predicted local and integrated tritium production rates (TPR) from ⁶Li(T₆), ⁷Li(T₇) and natural lithium (T_N) were compared to measurements in various configurations that included reference, first wall and beryllium multiplier experiments (Phase IIA) in addition to repeating these experiments with a FW/Be layer covering the interior surface of the Li₂CO₃ enclosure (Phase IIB). Other neutronics parameters that included source characterization by foil measurements, in-system reaction rates, and in-system spectrum measurements were also analyzed. The analyses were carried out independently by both parties using various 3-D Monte Carlo codes and 2-D discrete ordinates codes and data libraries. The results of the analyses are reported in this paper with emphasis placed on the impact of the beryllium data on the discrepancies found between predictions and measurements.