Neutron Generation and Diffusion Process in Reactors Stimulated by High Energy Proton Beam--The Accelerator Driven System

The neutron generation in the Accelerator Driven System (ADS) is discussed regarding the spallation reaction mechanism induced by the incidence of a high energy proton beam on the reactor core. We simulated the reaction process by a Monte Carlo calculation, employing an intranuclear cascade phase coupled to the nuclear evaporation regime. A new aspect is introduced with the incorporation of nucleons effective mass to mimic effects of nuclear medium on the nucleon kinematic. We show that reasonable changes in the nucleon effective mass can lead to a significant change in the characteristic of neutron source, with implications to the neutron transport regime of the reactor. A simplified neutron diffusion analysis of the subcritical reactor regime was recently reported in Ref. [1]. We improved this approach describing the neutron transport by two-energy group method to solve the diffusion equation. We have shown that even by applying a two-energy group treatment it is still possible to obtain an analytical solution of the neutron diffusion problem. The solution allows a clear discussion of changes in the reactor power for different levels of subcriticality. We calculated for a spherically symmetric geometry the flux along the radial distance and the power for different subcriticallity level and for a range of established values of the source current.