The diffusion equation arising from neutronics is an elliptic partial differential equation of the form -div(p grad u) + c u = f. Continuous second order, second order hybrid, mixed and mixed-hybrid formulations are investigated theoretically, each of them in a primal and dual version. A nodal finite element scheme is applied to the mixed-hybrid formulations. Well-posedness is investigated each time. A linear system is obtained, and early numerical results are provided.