Abstract: Before the 10MW pebble-bed High Temperature Gas-cooled Reactor-Test Module （HTR-10） reached the first criticality, the prediction calculations of the fuel loading of the core was a main physics design concern. In order to ensure the reliability of the physics design, verification calculations with Monte Carlo code MCNP has been carried out. Firstly, the sophisticated structure of the fuel element and reactor were descripted approximately and rationally, based on the HTR-10 characteristics. Then, the parameters of the eigenvalue calculation were chosen rationally, including number of cycles to be skipped before beginning, nominal source size per cycle, and number of cycles for calculation of eigenvalue; and the effect of different descriptions for HTR-10 fuel element structure was studied. Finally, the better scheme was determined.
The results of the scheme showed that under the atmosphere of air with a temperature of 27℃, the results of prediction calculation for the number of spheres including the fuel elements and the graphite elements, using MCNP and VSOP, were 16864 and 16821, respectively,with a relative error of 0.25%. According to the results of the first criticality of HTR-10, the experimental and predicted results were agreed well with low relative error less than 1 %.