  In this paper a methodology is described to estimate multigroup neutron
source distributions which must be added into a subcritical system to drive it
to a steady state prescribed power distribution. This work has been motivated
by the principle of operation of the ADS (Accelerator Driven System) reactors,
which have subcritical cores stabilized by the action of external sources. We
use the energy multigroup two-dimensional neutron transport equation in the
discrete ordinates formulation (SN) and the equation which is adjoint to it,
whose solution is interpreted here as a distribution measuring the importance
of the angular flux of neutrons to a linear functional. These equations are
correlated through a reciprocity relation, leading to a relationship between
the interior sources of neutrons and the power produced by unit length of
height of the domain. A coarse-mesh numerical method of the spectral nodal
class, referred to as adjoint response matrix constant-nodal method, is applied
to numerically solve the adjoint SN equations. Numerical experiments are
performed to analyze the accuracy of the present methodology so as to
illustrate its potential practical applications.
