The incremental fuel cost for light water reactor power stations has been formulated and studied using the FAPMAN planning model developed earlier. The model carried out the linear programming and associated sensitivity analysis using the shadow cost information. The multistage nature and the dependence on the refueling scheme of the cost were properly dealt with by the model Numerical studies on typical boiling water and pressurized water reactors have demonstrated that the model can furnish adequate values for the incremental cost for the use of the system integration study of nuclear power stations.