This report contains the calculation of the number and spacing of poison columns required to hold a 105 pile in the following cases: (1) complete failure of horizontal rods, (2) complete failure of all rods. Using 10% Cd 90% Pb poison columns of 1.44 inch diameter, it is found that 17 poison columns are required to hold the pile in case of complete failure of horizontal rods, and 65 poison columns are required to hold the pile in case of complete failure of all rods.