Numerical investigation of the reactor pressure vessel behaviour under severe accident conditions taking into account the combined processes of the vessel creep and the molten pool natural convection

Parametric analysis of the failure of a VVER-440 vessel during a serious accident

“…An examination of individual aspects of thermal and deformation behavior of VVER vessels during similar accidents [1][2][3][4][5] has shown that the time and character of vessel deformation prior to failure are largely determined by the thermal conditions on the outer surface and by the minimum residual thickness in the zone of melting of its wall. The excess vessel pressure and the size of the melt zone have a decisive effect on the time to failure and on the deformation of the vessel during a serious accident.…”

“…• a matrix of numerical experiments was constructed and a thermal analysis of the structure investigated was performed with prescribed isothermal boundary conditions on the inner and outer surfaces of the vessel wall; the distribution of the vessel temperature was used for strength analysis; the thermal and strength states were simulated in an axisymmetric formulation by means of the ATM-VVR computational program; the creep model used in this program determines the level of damage in the volume of each finite element; this makes it possible to simulate the accumulation of damage in the destruction of the material of the vessel as the vessel deforms [3][4][5]7]; the model of the structure considered consisted of 1500 isoparametric 4-node finite elements; …”

“…Increasing the temperature of the outer surface of the vessel, as a rule, results in an increase of the vertical displacement of the bottom. Failure time of a VVER-440 vessel versus the excess pressure with temperature of the outer surface 773 (1, 2), 973(3,4), and 1050 K (5, 6) for the minimum residual thickness of the vessel wall and melting zone size, respectively, 14 and 150 mm (1), 14 and 300 mm(2,3,5), 19 and 300 mm(4,6).…”