Development of the HELIOS/CAPP code system for the analysis of pebble type VHTR cores

Abstract The Korea Atomic Energy Research Institute is developing the HELIOS/CAPP code system for the analysis of a very high-temperature gas cooled reactor. The HELIOS/CAPP code system adopted a two-step core analysis procedure. In the first step, the HELIOS code is used to generate few-group cross section table sets, and in the second step, the CAPP code is used to perform core physics analyses. Some specific methodologies have been developed for the HELIOS/CAPP code system to treat some unique neutronic characteristics of the VHTR core such as the double heterogeneity effect and a strong fuel/reflector interaction. This paper introduces the specific methodologies and presents the development status of the CAPP code. The CAPP code has a multi-group neutron diffusion equation solver based on the finite difference method and finite element method. The functionality of the CAPP code has been extended on top of the flux solver to be able to perform a steady state core physics analysis and core depletion analysis. A specific module was developed to treat the tabulated cross-sections as a function of state variables such as burnup, fuel temperature, and moderator temperature. A simplified steady state thermo-fluid solver was developed for the thermal feedback calculation. A micro-depletion module was developed for the depletion analysis of a pebble type VHTR core. This paper also presents some verification results of the HELIOS/CAPP code system.