[en] MODIF-Code is a computer program for calculating the reflector saving, material buckling, and effective multiplication constant of completely reflected cylindrical reactors. The calculational method is based on a modified iterative algorithm which has been deduced from the general analytical solution of the two group diffusion equations. The code has been written in FORTRAN language suited for the ICL-1906 computer facility at Cairo University. The computer time required to solve a problem of actual reactor is less than 1 minute. The problem converges within five iteration steps. The accuracy in determining the effective multiplication constant lies within +-10^-5. The code has been applied to the case of UA-RR-1 reactor, the results confirm the validity and accuracy of the calculational method