Progress in Development of a Converging Beam Neutron Source for Driving a Sub-Critical Fission Reactor

Several laboratories are studying the possibility of a fission reactor system based on driving a sub-critical assembly using an accelerator-spallation target neutron source. The objective is to effectively eliminate possible criticality and meltdown accidents, increasing plant safety. However, one disadvantage is the large cost projected for the accelerator-driven source. In an ICONE-8 paper we proposed to overcome this problem by use of a Converging Beam Neutron Source (CBNS) to produce 14-MeV D-T fusion neutrons to drive the sub-critical core. [1] The CBNS is analogous to an accelerator-plasma target device with built-in re-circulation of the ions. It offers the unique advantage of being small enough to allow insertion of multiple 'modular' units in fuel channel locations (cf. the large single target used in accelerator-drive designs). As proposed in an ICONE-9 paper, a first important step in development of such systems might be use in low power research reactors. [2] This reduces the neutron source strength requirement to a level only slightly above that obtained with present IEC experiments. Still, a key step for CBNS development is to increase the neutron production efficiency obtained in previous small-scale experiments. To do this we have recently developed a unique RF-driven ion source so that the ion production region can be separated from the main CBNS chamber. This has the combined advantages of allowing ion production at relatively high pressure, while the CBNS chamber can be pumped to ultra-low pressure. Initial experiments with this arrangement are presented here and it is shown that a very favorable scaling to the yields required for research reactor operation are predicted. (authors)