In the analytical calculation of criticality by 3 group method, the equation which determines buckling may have, in general, complex solutions. For the positive real buckling, the flux has the same form as is given in the usual bare reactors, and has an oscillatory character, and for the negative real buckling, the flux has an exponential character. For the complex buckling, however, the flux contains both an oscillating and an exponential part. These forms have been deduced explicitly for some typical reactor geometries. No other forms of functions as shown here does appear if the number of groups becomes greater than three.
