[en] The local power distributions in a unit flow control region with and without a pair of control rods were analyzed for back-up cores of the Experimental Multi-Purpose Very High Temperature Gas Cooled Reactor by use of the point lattice burn-up code DELIGHT-IV and the two-dimensional transport code TWOTRAN-II. The following were revealed: (1) In modeling the cross section of a control rod by square shape, the equi-surface model is desirable for evaluation of multiplication constants and the equi-volume model for evaluation of power distributions. (2) A homogeneous model of the fuel elements is conservative in core design compared with the heterogeneous one, because of the underestimation of a control rod worth and the overestimation of a local power peaking. (3) The diffusion model estimates the control rod worth accurately with mean cross sections of the fuel elements and control rods. (auth.)