Analysis for Heterogeneous Blankets and Comparison to Measurements: Phase IIC Experiments of the USDOE/JAERI Collaborative Program on Fusion Neutronics

Abstract

Effort in Phase IIC of the US/JAERI Collaborative Program on Fusion Neutronics was focused on performing integral experiments and post analyses on blankets that include the actual hetergeneities found in several blanket designs. Two geometrical arrangements were considered, namely multilayers of Li₂O and beryllium in an edge-on, horizontally alternating configuration for a front depth of 30 cm, followed by the Li₂O breeding zone (Be edge-on, BEO, experiment), and vertical water coolant channels arrangement in which one is placed behind the first wall and two other channels (width of 0.5 cm each) are placed at depths of 10 and 30 cm from the first wall (WCC experiment). The objectives are to experimentally verify the enhancement in tritium production in the first experiment and to examine the accuracy of predicting tritium production and other reaction rates around these heterogeneities in the two experiments. In the BOE system, it was shown that, with the zonal method to measure tritium production from natural lithium (Tn), the calculated-to-measured values (C/E) are 0.95 − 1.05 (JAERI) and 0.98 − 0.9 (U.S.), which is consistent with the results obtained in other Phases of the Program. In the WCC experiment, there is a noticeable change in C/E values for T₆ near the coolant channels where steep gradients in T₆ production are observed. The C/E values obtained with the Li-foils to measure T₆ are better than those obtained by the Li-glass method. As for T₇, calculations and measurements by NE213 method are within ± 15% in JAERI's analysis, but larger values (∼ 20–25%) are obtained in the U.S. analysis. Around heterogeneities, the prediction accuracy for T₇ is better than that for T₆. In both experiments, the prediction accuracy for high-threshold reactions [(e.g. ⁹³Nb(n,2n)] is within ± 10% as obtained by both Monte Carlo and Sn codes, however, it was shown that the ⁵⁸Ni(n,2n) cross-section of ENDF/B-V should be increased by 25–30% at high incident neutron energies to give better C/E values.