The unique core and reflector structure of the inverse flux trap research reactors has raised a challenge to the traditional deterministic neutronics calculation methods applicable to power reactors. The deterministic codes DRAGON/DONJON with powerful geometric modeling capabilities have been maturely applied to power reactor types such as CANDU (Canadian Deuterium Uranium) and pressurized water reactors (PWR), but not been performed neutronics calculations and feasibility analysis on the China Advanced Research Reactor (CARR) with inverse flux trap design.

This study aims to verify the feasibility of the DRAGON/DONJON codes in CARR neutronics calculations and analysis.

Firstly, when performing homogenization calculation using DRAGON/DONJON codes on various assemblies of CARR, the multi-assembly method was adopted to improve the surrounding impact. The OPTEX reflector optimization method was used to modify the homogenization constants of the reflector. Then, the commonly used multigroup cross-section libraries in DARGON were compared and screened, and SHEM-295 group-structure library was selected. Finally, the calculation results of DRAGON/DONJON codes were compared with the Monte Carlo references and the conventional three-step method, and analysis was conducted on the reasons for the significant deviation in the calculation results.

The results indicate that the deviation of parameters such as k_eff eigenvalue near critical operating condition, thermal neutron flux distribution in the active zone of the core and the middle position of the heavy water tank, and power distribution of standard fuel assemblies are relatively small whilst significant deviations in the calculation results appear at the junction of the core and heavy water tank, the vacuum boundary outside the pool, and the follower assemblies.

This study verifies that it is feasible to use the DRAGON/DONJON codes for CARR neutronics calculations and achieve a certain degree of accuracy, meeting the needs of experimental schemes design and rapid calculation and analysis of operating parameters.