CFD simulation of steam generator tube rupture thermal-hydraulics

Several steam generator tube rupture accidents have occurred at plants in the past. In this paper the Computational Multi-Fluid Dynamics (CMFD) investigation of the horizontal steam generator thermal-hydraulics during the tube rupture accident is performed. A guillotine of a steam generator U-tube is assumed with choked flow from the primary to the secondary side of the steam generator. We have computed water and steam velocity fields, steam volume fraction distribution on the steam generator secondary (shell) side, as well as the swell level increase. The simulation results are a support to the safety analyses of the steam generator tube rupture accident. Numerical simulation is performed with the multidimensional multi-fluid modelling approach. The two-phase flow around steam generator tubes in the bundle is modelled by the porous media approach. Interfacial mass, momentum and energy transfer are modelled with the closure laws. The governing equations are solved with the SIMPLE type pressure-correction method that is derived for the conditions of multi-phase flow conditions. The following results are drawn from the simulation. Although the two-phase leakage exists at the break, a gradual decrease of the void fraction in the region of the U-tube ruptures is obtained which is the result of the liquid phase inflow at the break. As expected the void fraction decrease is more intensive after the additional break of two more tubes. A two-phase swell level is predicted from the void fraction calculated results, it is located on the horizontal steam generator hot side, just above the rupture location. After the first U-tube rupture the swell level oscillatory changes within a 0.1 m height for the period of 800 s. There is no considerable change in the water velocity vectors in the area of tube bundles after the first tube break. Above the perforated plate the water velocity field is changed due to the swell level increase. At nominal power, the water flows from the hot towards the cold side and this flow direction is also maintained after the break