Numerical Simulation and Analysis of In-Leakage in a Nuclear Power Plant Main Control Room via CFD

This study systematically investigates the influence of air exchange rate and tracer gas injection concentration on equilibrium time and mixing uniformity during in-leakage measurement of a nuclear power plant main control room (MCR). A combined approach of computational fluid dynamics numerical simulation and on-site measurement was employed. The results indicate that a higher air exchange rate (in-leakage rate) leads to a shorter time for the tracer gas to reach equilibrium concentration, demonstrating a negative correlation between equilibrium time and the air exchange rate. To address the issue of prolonged measurement cycles in third-generation nuclear reactor types, a strategy of increasing the tracer gas injection concentration is proposed. This strategy can significantly reduce the equilibrium time to within 6 h, meeting the requirements of on-site shift cycles. The study also reveals that an elevated injection concentration results in a decrease in spatial mixing uniformity. Therefore, it is necessary to implement forced mixing measures, such as fans, to achieve the required uniformity criterion of ±10%. The comparison between experimental measurements and numerical simulations shows that the concentration trends are generally consistent, with relative errors in equilibrium concentration and equilibrium time within 10%, thereby validating the accuracy of the mathematical model. This research demonstrates that high-concentration tracer gas injection combined with forced mixing measures can significantly enhance detection efficiency while ensuring measurement precision. It provides a reliable method for the efficient on-site assessment of the habitability boundary in nuclear power plant MCRs. The numerical simulation approach offers effective theoretical guidance and technical support for formulating practical measurement protocols.