A Simplified Model and MATLAB Code for Modelling Mo-99-Producing CANDU Bundles in the Context of an Undergraduate Nuclear Engineering Design Course

Abstract

Undergraduate-level nuclear engineering design courses focus, among other things, on elements of fuel bundle design. Real-life CANDU fuel-bundle design involves performing accurate neutronic and thermalhydraulic calculations by using neutron-transport codes, sub-channel-level hydraulic codes and solving the heat-conduction equation explicitly in each fuel pin. Allowing undergraduate students to simply use such codes as black boxes is unsatisfactory from a pedagogical perspective, while involving students in the development of such codes is usually beyond the scope of an undergraduate course. At the same time, the problem is complicated enough as not to be amenable to a purely analytical solution. Under these conditions, a fruitful approach is to use simplified models which undergraduate students can use to develop simple numerical computational tools. This work presents the development of a simplified model and MATLAB code which calculates the infinite multiplication factor, pin power distribution, fuel centerline temperature and Mo-99 yield for a CANDU-type bundle for different fuel pin radii, pitch circle radii and fuel enrichment. The model uses a Wigner-Seitz equivalence between a square lattice cell and a circular one. The latter is subsequently analyzed using one-group one-dimensional diffusion in cylindrical geometry. The diffusion equation is discretized using finite differences. The inverse-power iteration method is used to calculate the infinite multiplication constant and flux. The resulting flux is used to calculate the power, fuel temperature and Mo-99 production in each fuel ring.