Spallation neutron sources, though very effective in neutron production, are large, expensive and presently would involve certain difficulties in their operation (e.g., beam trips). Contrary, an electron driver, although much less effective in neutron production, is rather cheap and compact machine that, at the same time, might bring advantages in terms of reliability. Here we investigate the use of an external neutron source (irradiator) driven by an electron accelerator. A schematic layout and design of a compact neutron irradiator is proposed with its neutronics and safety being analyzed and discussed in detail. The system is based on a spherical geometry with an electron beam interacting with the target-envelope. Neutrons are produced in the natural or enriched uranium by photonuclear reactions. The system is well sub-critical (Keff < 0.8) and uranium enrichment is below 20%. Neutron balance is optimized by using different geometry and material configurations. Our preliminary calculations show that variable (up to 10% thermal and/or up to 30% with energies higher than 1 MeV) neutron fluxes of a few
10^14 n/(s cm^2) could be obtained for different irradiation purposes. An electron machine of
~8 MW power and 100 MeV incident energy should be sufficient to produce external neutrons to drive the system. |
