A coupled and transient calculation method for a posteriori evaluation of coarse-mesh boiling water reactor core calculation results was developed. An analysis of the local power density shape in the environment of the topmost end of the control element was made. The influence on the sections of the fuel pins being exposed by a small control-element withdrawal has been investigated. The transient calculation results of response in the power density to a 16-cm-long, 4 cm/s speed control-element ramp are discussed.