The integral transport equation is first formulated for a Wigner-Seitz reactor lattice cell with either reflected or isotropic return boundary conditions. The equation is then reduced to a form suitable for numerical computation by dividing the cell into a number of concentric volume increments and approximating the scalar flux within each of these by a three point interpolation polynomial. The procedure thus relaxes the flat flux assumption made for each volume increment in using conventional collision probability methods. One group disadvantage factors are calculated for a slab and a cylindrical lattice using both the collision probability and the polynomial approximation methods. The polynomial approximation technique results in a substantial reduction in the computing time necessary to obtain the disavantage factors to within a given accuracy.
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