DETERMINATION OF THE THERMAL NEUTRON FLUX DISTRIBUTION IN A HEXAGONAL LATTICE CELL.
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OHIO SCHOOL OF ENGINEERING
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Thermal neutron flux distributions were obtained in hexagonal and square lattice cells by a finite difference approximation to the diffusion equation. The grid network used to approximate the lattice cells was created from a combination of cylindrical and cartesian coordinate systems to facilitate the handling of the normal boundary conditions at the rod surface. Square lattice cell flux distributions for non absorbing media compare favorably to those predicted in an analytic solution by Cohen. Marked deviations in this result occur as absorption is increased. Hexagonal and square cell flux distributions agreed within 1.5 per cent to the results predicted by the cylindricalization technique at interior points in the cell for all cases of absorption studied. Large deviations in flux distributions along the cell boundaries indicate that errors may arise in calculations of the thermal utilization based upon the cylindricalization assumption. Deviations in all results near the rod surface are attributed to truncation error or normalization technique. Author