Experiments were undertaken to determine the distribution of neutron flux on the core support grid plate of liquid-metal fast breeder reactors by using a semimockup of the grid-plate shield consisting of carbon-steel and aluminum slabs. The experiments were calculated with a conventional calculational procedure containing the TRD-3 two-dimensional removal diffusion code. It was demonstrated that the calculated radial distribution of the fast neutron reaction rates of 115In(n,n′)115mIn agreed with the measured values within a factor of 2.