Determinação de Fontes de Nêutrons que Conduzem Sistemas Subcríticos a Distribuições Prescritas de Potência

ABSTRACT

A nuclear system is referred to as subcritical when neutron removal events (leakage through the boundaries of the system and absorption) occur at a rate which is greater than the events that promote the production of these particles (fission). When this occurs the system cannot maintain a stable level of the population of neutrons and tends to shutdown. On the other hand, any subcritical system may be driven by one or more stationary sources of neutrons. The purpose of this work is to present a methodology to determine the intensities of the stationary and uniform sources of neutrons that must be inserted in a subcritical system to drive it to generate a prescribed power distribution. To achieve this goal, we use the time-independent, slab-geometry, one-speed neutron transport equation as a mathematical model in multiplying media, referred to as forward problem, and the equation which is adjoint to it, both in discrete ordinates (S_N) formulation. The coarsemesh adjoint response matrix (RM^†) method is applied to numerically solve the adjoint S_N problems. The RM^† method is a companion method of the response matrix method used to solve forward S_N equations. Numerical results for two typical model problems are presented to verify the offered methodology.

Keywords:
discrete ordinates; adjoint problem; adjoint response matrix; subcritical systems