  This paper presents a computational scheme for the determination of
equivalent 2D multi-group heterogeneous reflectors in a Pressurized Water
Reactor (PWR). The proposed strategy is to define a full-core calculation
consistent with a reference lattice code calculation such as the Method Of
Characteristics (MOC) as implemented in APOLLO2 lattice code. The computational
scheme presented here relies on the data assimilation module known as
"Assimilation de donn\'{e}es et Aide \`{a} l'Optimisation (ADAO)" of the SALOME
platform developed at \'{E}lectricit\'{e} De France (EDF), coupled with the
full-core code COCAGNE and with the lattice code APOLLO2. A first validation of
the computational scheme is made using the OPTEX reflector model developed at
\'{E}cole Polytechnique de Montr\'{e}al (EPM). As a result, we obtain 2D
multi-group, spatially heterogeneous 2D reflectors, using both diffusion or
$\text{SP}_{\text{N}}$ operators. We observe important improvements of the
power discrepancies distribution over the core when using reflectors computed
with the proposed computational scheme, and the $\text{SP}_{\text{N}}$ operator
enables additional improvements.
