Simulation of the HTR-10 reactor core with spherical fuel to obtain the minimum height to access reactor criticality

The HTR-10 reactor is an experimental Pebble bed reactor, in which the simulation of the neutron flux for this reactor is very important due to several advantages of this type of reactor. One of the advantages is safety and high efficiency and its modularity. Therefore, one of the important and significant issues of the countries with nuclear technology is the study and research on this type of reactors in order to commercialize them. Since the fuel and moderator in the reactor are in the form of spherical spheres and are randomly distributed in the core, it is very important to evaluate the neutron flux of this reactor by calculating the minimum height necessary for the criticality of the reactor according to the type of arrangement of fuel and moderator. Therefore, in this research, a new method for the arrangement of fuel and moderator pellets  with keeping the ratio of 43:57 has been proposed. The calculations are performed using the MCNP code. Helium gas is considered as a coolant and changes in reactivity due to the entry of control rods have been calculated.