Speaker
Description
In recent years, the development of high-current accelerator-based neutron sources (HiCANS) has gained in interest to propose an alternative to research reactors. In HiCANS high neutron yields are achieved by irradiating metal targets with proton beams with energies in the MeV range bellow the spallation threshold and currents of several tens of milliamps. Based on this concept, the High Brilliance neutron Source (HBS) project was developed at Forschungszentrum Jülich to deliver a high flux of neutrons to various scattering, analytics and imaging instruments.
In HBS, fast neutrons are induced by the (p,xn) reaction in a tantalum target irradiated with 70 MeV protons at a peak current of 100 mA. The fast neutrons are thermalized into a water moderator surrounded by a lead reflector and a shielding. Finally, the optimized thermal and cold neutrons are passed through the neutron guides and fed to the instruments.
The shielding design of the target system is considered from the point of view of radiation protection. The shielding components consist of four layers of lead and four layers of borated polyethylene housed in a steel casing. In addition, the bunker walls of the target room, in which the target system and shielding is placed, are considered as a secondary shielding. These walls consist of 70 cm of concrete doped with polyethylene and an additional 70 cm of borated concrete.
The entire target room is modelled and the CAD model is converted into Monte Carlo inputs (mcnp6.1 and phits3.27) for particle transport simulation. The dose rate map, neutron and gamma flux distribution in the target room and also at the outside of the bunker walls are calculated during beam operation and also when the beam is switched off. The aim of shielding design is to restrict the dose rate in the supervised area well below the radiation protection criteria. The detailed analysis of the data will be presented.