[en] A symbiotic energy system between a GCFR based on uranium-thorium mixed cycle and several VHTRs on thorium cycle appears to be promissing as an energy supply system self-sufficient in fuel to produce both electricity and high temperature process heat. We have been proceeding design study of the GCFR core suitable for the above mentioned symbiotic system. In the present paper, we selected a reference GCFR core with 19 control rods, basing on the investigation of various GCFR core concepts made in the previous paper. On the reference GCFR core selected, we investigated reactivity worth of the control rods and power distribution, and we set up a control rods insertion pattern in the core at the beginning of the equilibrium cycle (BOEC). Thermo-hydraulic characteristics of the core were analysed, taking account of power distribution distortion caused by control rods insertion into the core. The neutronic analysis indicated that the reactivity required for the primary and secondary systems to be controlled could be controlled by using the 19 control rods adopted in the study. And, from the thermo-hydraulic analysis including evaluation on hot-spot temperature for the core at BOEC, it was indicated that the maximum fuel pellet temperature could be well bellow the fuel melting temperature, and also that the maximum cladding temperature could be kept at the appropriate one. (author)