ADJOINT NEUTRON-SPECTRUM CALCULATION FOR HETEROGENEOUS CELLS

Forward spectrum weighting has been used to generate broad-group cross sections. However, for some applications of perturbation theory, the adjoint spectrum is needed. Recently an approximate method has been pr oposed for the adjoint spectrum in a lattice cell, based on an equival ence principle. The approximations made can be avoided if the neutron energy dependence is treated in detail, and the neutron transport thro ugh the regions of a lattice cell is adequately represented. In this p aper the neutron balance adjoint equations are derived for a heterogen eous unit cell based on the collision probabilities method, and the ad joint spectrum is calculated from this system of equations for differe nt intervals of energy. Forward and adjoint spectra comparisons are do ne for a unit cell having U-238 in its inner region. in the numerical applications of the neutron balance adjoint equations the most importa nt resonances of U-238 were considered. The results show significant v ariations between the forward and adjoint spectra, leading to remarkab le differences in the effective resonance integrals.