Startup transients in accelerator driven systems using cinesp-ads code

Accelerator Driven Systems (ADS) are subcritical nuclear reactor cores driven by spallation neutron source. These spallation neutrons are provided from the bombardment of a liquid metal flowing in a central region of the core, by a proton beam coming from a linear accelerator. Since neutron source dominates the neutronic of the ADS, its control usually is not related to the delayed neutron fractions as in the critical systems. In this way, ADS kinetics diverges from the former ones. This work presents some results of transients in ADS. Since ADS is to work in a pulsed regime, with time duration of pulse, a parametric result is showed to point out that different pulse durations should be studied in conjunction with pulse intensity, to maintain the ADS power stable. In addition, before generating these results, some transients were used to validate the CINESP-ADS code. It solves numerically the kinetic equations based on the multigroup diffusion theory, in One- or Twodimensional, in the Cartesian or Cylindrical geometries, and for any energy and delayed neutron groups. Threedimensional simulation is possible using a reactor transversal buckling. The numerical solution is obtained via finite differences for the spatial discretization, using the so-called box integration, and with the use of Alternating Direction Explicit (ADE) methods, for the time discretization. The code application to some transients due to source neutron variations demonstrates its efficiency and accuracy, when compared with analytical techniques, such as one that uses expansion in series of Helmholtz eigenfunctions