Evaluation of power distribution calculation of the very high temperature reactor critical assembly (VHTRC) with Monte Carlo MVP3 code

•Power distribution plays a significant role in high-temperature gas-cooled reactors.•Experiments for measuring the power distribution were performed at the VHTRC.•Power distributions determined with Monte Carlo showed large improvement toward predictions with diffusion.•Pin-wise power distribution of VHTRC was evaluated with the Monte Carlo MVP3 code.•The Monte Carlo calculation showed a good agreement with the experimental data. Power distribution plays a significant role in preventing the fuel temperature from exceeding the safety limit of 1600 °C in high-temperature gas-cooled reactors. Experiments for measuring the power distribution in the graphite-moderated system were performed at the Very High-Temperature Reactor Critical Assembly (VHTRC) facility. The power distribution was determined from the measured Cu activation rate for both the radial and axial distributions. In this study, the pin-wise power distribution of the VHTRC was evaluated with the Monte Carlo MVP3 code. The difference between the calculated and measured results was less than 1 % for the axial and radial distributions. The significant results were concerned with the area around the fuel and reflector regions in the axial direction, where the average discrepancy between the calculated and measured values was 0.8 %. This result showed improved agreement compared to the diffusion calculation that was conducted in the previous study.