Phase-IIB Experiment of JAERI/USDOE Collaborative Program on Fusion Blanket Neutronics

As a part of the Phase-II experimental series of JAERI/USDOE collaborative program on fusion blanket neutronics, the phase-IIB experiment has been performed. The experiment provides information of neutron multiplication and reflection by the inner berryllium layer in a full-coverage blanket geometry. The measurements were carried out at the positions in the test zone on tritium production rate (TPR) using various methods, on reaction rate using foil activation technique and on neutron energy spectrum using NE213 and gas proportional counters. The experimental results showed that the effect of the full-coverage beryllium was a 10% increase for T₇ (TPR for ⁷Li) and a factor of 2–5 increase for T₆ (TPR for ⁶Li). The increase of the integrated TPR for natural lithium (T_n) in the test zone due to the inner beryllium layer was above 60% compared to the non-beryllium system in the Phase-II geometry.