A Multigroup Albedo Method for Transport Calculations: Application to the Orphee Core

Through the introduction of appropriate boundary conditions, the use of multigroup albedos permits one to concentrate the numerical effort of solving the transport equation in only the domain of interest, thus reducing computational requirements. Multigroup albedos that are representative of an external medium can be calculated via independent transport calculations and collapsed for use in a fewgroup three-dimensional transport calculation. The multigroup albedo method is developed and applied to the calculation of the Orphee research reactor. Numerical comparisons between full-core two-dimensional transport calculations and two-dimensional transport calculations performed with multigroup albedos show why the method is interesting. The axial power distribution obtained from a three-dimensional transport calculation with multigroup albedos precisely matches measured experimental values, while results from three-dimensional full-core diffusion calculations give unacceptable errors.