A method based on interface current formalism has been developed for solving the integral transport equation for cylindered pressurized heavy water reactor fuel lattices. In this a fuel cluster is divided into various rings, which are further subdivided into homogeneous zones like fuel, cladding, and associated coolant. The region outside the fuel cluster is also divided into a number of concentric annular (homogeneous) regions. A cosine current approximation is assumed at all the interfaces of the rings and annular regions while interactions between zones within a ring are directly calculated by the Pij method. In addition to this, the usual flat flux approximation is assumed for each of the homogeneous zones/regions. Based on this method, we have developed a one-group code, ANPROB, for calculating the flux distribution. The results obtained from the present method for 19- and 28-rod cluster lattices have been compared with the exact collision probability (Pij) method for clusters. It is found that the present method reduces the computational time considerably without sacrificing much of the accuracy.