Research on leakage and migration behavior of 87Kr/135mXe in the Molten Salt Reactor containment

Abstract

Effective monitoring and control of radioactive gas leakage are crucial for the safe operation of Molten Salt Reactors (MSRs). The liquid fuel in MSRs increases the mobility of radioactive materials. Therefore, predicting the migration and leakage of volatile radioactive products from primary system boundaries is essential. This study, for the first time, focuses on the migration behavior of radioactive gases within the MSR containment during the first 2 h following the appearance of small leaks. Using the FLUENT software, the research investigates the influence of gas flow fields, leakage locations, and decay characteristics on the transport of these radioactive gases, particularly ⁸⁷Kr and ^135mXe. The results indicate that pre-existing gas flow fields significantly affect the distribution and migration of radioactive gases, leading to a more uniform concentration distribution. Furthermore, the concentration ratios of ⁸⁷Kr to ^135mXe exhibit a near-linear increase with leakage time, with the specific magnitude of increase being strongly correlated with leakage locations. When the initial leaking concentration ratio of ⁸⁷Kr to ^135mXe is set at approximately 1.70, the concentration ratios for leakage locations (i.e., point 1, point 2, and point 3) increase to 1.81, 1.86, and 1.89 at 3 min after leakage, and to 5.90, 6.80, and 7.94 at 2 h after leakage, respectively. This study proposes a novel monitoring approach based on the concentration and concentration ratios of ⁸⁷Kr and ^135mXe for MSRs. This approach provides valuable information for leakage diagnosis, such as leakage time, location, and flow rate, and offers technical support for the radiation monitoring and safe operation of MSRs.