In this work, the characteristics and properties of spallation targets in ADS (Accelerator Driven System) are investigated. The objective is to obtain a high neutron flux with a hardened neutron spectrum for transuranic transmutation in a hybrid ADS-fission systems purposes. The proposed system uses a source of protons with energies between 0.3 to 1.6 GeV focusing on liquid targets such as mercury (Hg), natural lead (Pb) and a eutectic lead-bismuth alloy (LBE). The dimensions of the spallation target (radius R and length L) were modified to better understand the role of these variables in neutron yield. The neutron flux on the surface of the targets is evaluated for different energies of the incident protons and different target geometries considering the results of the simulations in MCNPX. The results show a neutron multiplicity saturation limit for incident beam energy at 1 GeV. It is verified that there are optimal dimension values for the target radius and length, respectively, at R close to 15 cm and L close to 50 cm for incident proton energies of 1 GeV. The graphical distribution of the neutron flux is also shown using the software MATLAB.

A subcritical hybrid system of the ADS type [1] was used in criticality analysis to verify the influence of different descriptions of spallation and fission sources that can be modeled with the MCNP6.2 code. For this, 11 different configurations of sources were simulated and the analysis of their effective multiplication factors (𝑘𝑘 𝑒𝑒𝑒𝑒𝑒𝑒 ) and Shannon entropy (𝐻𝐻) were performed. The rapid convergence of 𝑘𝑘 𝑒𝑒𝑒𝑒𝑒𝑒 and 𝐻𝐻 values for the simulated sources demonstrate that the population of fission neutrons in the reactor core is predominant, regardless of the modeling used for the external source in the criticality calculations. Therefore, a more simplified description of the hybrid font in the ADS system, with only the spallation font modeled in the system, can be adopted.