Analysis of three-dimensional flow field and reactor vessel impact failure in sodium-cooled fast reactor core disruptive accident

Following a core disruptive accident (CDA) in a pool-type sodium-cooled fast reactor, a high-energetic gas cavity forms at the core region and undergoes rapid volumetric expansion within milliseconds. This transient hydrodynamic phenomenon displaces liquid sodium coolant and applies substantial impulsive loads to the main vessel's upper shielding cover, potentially exceeding its structural integrity limits. To accurately investigate the multiphase flow state and structural response mechanisms during the accident, this paper employs a fluid–solid coupling methodology integrating the computational fluid dynamics (CFD) software FLUENT and the finite element analysis (FEA) package ABAQUS, enabling cross-scale coupling calculations via dynamic load transfer, from macroscopic flow field characteristics to millimeter-scale sealing structure behavior. The study elucidates the characteristics of various phases of the accident. In the initial phase, the positive reactivity induced by core disintegration leads to an exponential increase in gas cavity pressure and temperature. During the expansion phase, the shock pressure of liquid sodium impacting the bottom of the plug exhibits two pronounced high-pressure peaks (transient maxima: 14.5 MPa). These coupled thermo-mechanical phenomena originate from energy − concentrated two-phase interactions at the gas–liquid interface and viscous dissipation in transverse flows induced by boundary-layer separation effects. In the structural response phase, transient impacts result in millimeter-scale local deformations in the shielding cap, leading to localized deformation at the plug-cover junction. This may create a potential leakage channel with a gap width of 1.02 mm (millimeter-scale), allowing the internal argon and sodium to be ejected from the containment vessel through the gap. The findings of this study provide a significant theoretical foundation and data support for the analysis and assessment of CDAs in pool-type sodium-cooled fast reactors.