Three-dimensional discrete heterogeneous finite element method and code for static multi-group neutron diffusion

Accurate prediction of the neutron flux and power at the fuel pin level rather than at the fuel- assembly level requires, in principle, lengthy many-group transport-theory calculations using a detailed (fuel-pin level) geometrical representation of the core. Many-group fine-mesh diffusion theory, in conjunction with advanced fuel-pin-cell homogenization techniques, can also be used successfully to predict individual fuel pin powers but the computational effort is still sizeable because of the many regions and groups involved. A three dimensional diffusion code was developed which reduces the time taken by such full-core fine-mesh fine-group diffusion calculations by applying the finite-element method to the discrete form of the many-group fine- mesh diffusion equation and thus reducing the number of unknowns. Preliminary tests performed on a highly-heterogeneous three dimensional three-group model found the code to produce pin power results with a maximum error of 3.5% of the maximum pin power value, with an eight-fold reduction in computational time compared to a regular full-core fine-mesh calculation. (author)