Experimental results for Phase II of the JAERI/USDOE collaborative program on fusion blanket neutronics

As the first period of the Phase II series of the JAERI/USDOE collaborative program, neutronic parameters have been measured for a simulated Li2O/Be breeder blanket in closed geometry. The experimental system consists of a lithium-oxide test zone and a lithium carbonate enclosure containing a DT neutron source at the Fusion Neutronics Source (FNS) facility at JAERI. Tested blankets were of three 5 cm thick configurations of beryllium neutron multiplier zone. The experiments were performed to examine spatial distributions of reaction rates and the neutron spectrum in the source cavity, and relative profiles of the tritium production rate (TPR), reaction rates, and neutron spectra between the beryllium configurations. A zonal TPR measuring technique, suitable especially for direct comparison with a Monte Carlo method, was applied to a steep gradient distribution. The experimental results of TPRs showed that the beryllium sandwiched system provided the most effective TBR gain (integrated TPR) of about 20% compared with the non-multiplier system. The reaction rate distributions and neutron energy spectra were also provided to test a calculational code system for nuclear design.