A mechanistic analysis code for aerosol migration behavior associated with a large-scale bubble during a core disruptive accident

Abstract

The potential release of radioactive materials is a crucial design consideration for advanced reactors, especially for minimizing environment impact during severe accidents. In this context, studying the release of radioactive materials from the sodium pool during a core disruptive accident (CDA)—the most severe accident in a sodium-cooled fast reactor—is of significant value. During a CDA, fission products can migrate as aerosol particles through the sodium pool to the cover gas region in a short time (approximately a few hundred milliseconds) along with a large-scale, multi-phase, multi-component bubble generated after the core recriticality. To address this issue, we developed a code to simulate the migration behavior of aerosols with the large-scale bubble within the sodium pool. The code is based on a one-dimensional two-phase multi-component CDA bubble model and integrates an aerosol migration model to explain the process of aerosol particle absorption by the coolant. Using analysis results of the core provided by the internationally recognized severe accident analysis program SIMMER as boundary input conditions, the code was used to implement a trial calculation of the in-vessel migration of the representative fission product cesium during a CDA in a prototype sodium-cooled fast reactor. In the case where cesium and sodium were immiscible, the overall computational results showed good consistency with the results from the SIMMER code, indicating the applicability of our code. Therefore, by accounting for the unique miscibility characteristics of cesium and sodium in the code, the final amount of cesium migration could be determined.