Evaluation of symbiotic energy system between gas-cooled fast breeder reactor (GCFR) and multi-purpose very high temperature reactor (VHTR), (2)

The present paper summarises the reactor physics work related to the equilibrium fuel cycle of the 1,000 MWe gas-cooled fast breeder reactor suitable for the GCFR-VHTR symbiotic energy system. Special attention is devoted to breeding performance and reactivity effects, all of which are calculated by using two dimensional R-Z diffusion and burnup codes together with JAERI-Fast 25 group cross-section Version II. The former performance includes charged and discharged fuel compositions during an equilibrium cycle, breeding ratio and doubling time of the symbiotic system. The latter includes reactivity effects of Doppler, material expansion, coolant He-loss and density reduction, and steam entry into the core. And also based on the above mentioned reactivity effect calculations, we set up the reactivity requirements for the control rod system of the reference GCFR core, and the reactivity feedback coefficients for the future kinetic analyses. Analyses on control rod reactivity worth and power distribution are excluded from the present paper, since they needs extensive three-dimensional calculations, considering control rod position. (author)