SUMMARY

The goal of this thesis is to develop a reconstruction (ESR) method for unfolding a coarse group energy spectrum to a continuous-energy spectrum with B-spline methods, and subsequently to an arbitrary fine group energy spectrum while preserving the neutron particle balance. Whole core calculations are commonly performed using diffusion theory with approximate coarse group cross sections that are generated by lattice cell calculations with approximate boundary conditions (e.g., zero-current/specular reflection). To correct these cross sections in absorber regions such burnable poison pins, commonly used in reactor designs, would require local transport calculations with the local fine group boundary conditions. It is this fine-group flux boundary condition that this research will reconstruct using the proposed new method. The objective of the ESR method is to construct the fine-group energy spectrum on the surface of selected regions (e.g., burnable poison pin) in the core as boundary condition for on-the-fly local transport (cell) calculation that would update absorber cross sections for the next iterate of the whole core coarse-group diffusion calculation. In summary, the proposed method will consist of using the B-spline method together with the least square method to normalize the reconstructed intra-coarse-group flux to a pre-computed whole-core averaged reference spectrum while preserving coarse-group particle balance on the surface of the selected absorber region. The method will be tested in a benchmark problem typical of the High Temperature Reactor. The specific application would be to correct the burnable poison pin cross sections for the effect of non-specular boundary condition found in HTR calculations.