4.1 Block Method Neutron Transport Calculation on x-y Geometry With Three-subregion Cell Model Xu Xiaoqin Based on neutron integral transport theory, a numerical model for multi-group neutron transport equation on x-y geometry with three subregions in each cell is developed with block method coupling interface current and collision probability techniques. In this model, for x-y geometrical reactor core composed of fuel lattices, collision probability method (CP or PIJ) is used to calculate neutron flux of cylindrical fuel rod, cladding, moderator in each lattice, and interface current technique is used to couple adjacent lattice with DP1 approximation. The model has advantages of high accuracy, short computer CPU and flexibility to treat different geometrical problems. It is one of the most suitable methods for power reactor assembly calculation. Based on basic theory of the method, numerical technique and theoretical model with 3-subregion cell are developed. Computer program is encoded. To check its accuracy and practicality two samples are calculated and compared with results of other programs. Comparison calculation shown good agreement between this program and other programs for power distribution and effective multiplication factor. 4.1 Block Method Neutron Transport Calculation on xy Geometry With Three-subregion Cell Model Xu Xiaoqin Based on neutron integral transport theory, a numerical model for multi-group neutron transport equation on xy geometry with three subregions in each cell is developed with block method coupling interface current and collision probability techniques. In this model, for xy geometrical reactor core composed of fuel lattices, collision probability method (CP or PIJ) is used to calculate neutron flux of cylindrical fuel rod, cladding, moderator in each lattice, and interface current technique is used to couple adjacent lattice with DP1 approximation. The model has advantages of high accuracy, short computer CPU and flexibility to treat different geometrical problems. It is one of the most suitable methods for power reactor assembly calculation. Based on basic theory of the method , numerical technique and theoretical model with 3-subregion cell are developed. Computer program is enc To check its accuracy and practicality of two samples were calculated and compared with results of other programs. Comparison calculation shown good agreement between this program and other programs for power distribution and effective multiplication factor.