Analysis of diffusion coefficient correction methods applied for small-core, high-leakage reactors

Nodal diffusion codes have been successfully used for decades as a primary tool of commercial power reactor design, safety calculations and plant cycle simulations. The large-size, small-leakage property of these reactor cores and the appropriately generated and applied auxiliary parameters (such as albedos, discontinuity factors etc.) provide a calculation environment, where diffusion theory is fairly accurate, giving the industry the ultimate advantage of fast neutronic computation. Recently, several efforts have been made to extend this methodology to small-core, high-leakage research reactors, in which the validity of diffusion theory is not straightforward. In this paper, the appropriate generation of the diffusion coefficients and their effect on the overall performance of the simulations are investigated in light of recent developments. For the numerical analysis, the two-dimensional DIMPLE benchmarks and the BME TR core benchmark problems were chosen. Group constants were generated with the Serpent 2 Monte Carlo code, while nodal diffusion calculations were carried out with the PARCS code. The results were assessed in terms of multiplication factor, assembly level power and two-group flux distributions.