In-Vessel Core Melt Retention Strategy Applied for the Rivne VVER-440 Unit

In-Vessel Core Melt Retention (IVMR) strategy via external vessel cooling is widely applied for reactors of relatively low power like VVER-440. In this study, IVMR strategy was applied for Rivne-1, 2 units to prove the pressure vessel integrity. Based on initial data like heat flux for internal wall and external wall temperature, a series of calculations for different scenarios were performed. These calculations include non-elastic material properties: creep and plasticity. As the result, the wall ablation, radial displacements, stress and strains were obtained. To prove pressure vessel integrity four criterions have been checked. The first one is obvious — remaining wall thickness, to prove that that RPV won’t be melted right through. The second one is visco-plastic collapse — lack of monotonous increase in deformations, in case of FEM solution result convergence can be interpreted as resist against such failure. The third — sustainable external cooling, thus the gap between RPV (due to radial elongation) and thermal protection shield must be 10 mm at least. The last one is brittle strength, this calculation was performed on a separate model.