Simulation of Scaled Vessel Failure Experiments and Investigation of a PossibleVessel Support against Failure

摘要

Scaled coupled melt pool convection and vessel creep failure experiments are being performed in the FOREVER programat the Royal Institute of Technology, Stockholm. These experiments are simulating the lower head of a pressurized reactor vesselunder the thermal load of a melt pool with internal heat sources. Due to the multi axial creep deformation of the three-dimensionalvessel with a highly non-uniform temperature field these experiments offer an excellent opportunity to validate numerical creepmodels. A Finite Element model is developed and using the Computational Fluid Dynamic module, the melt pool convection issimulated and the temperature field within the vessel wall is evaluated. The transient structural mechanical calculations are thenperformed applying a new creep modelling procedure. Additionally, the material damage is evaluated considering the creepdeformation as well as the prompt plasticity.After post-test calculations for the FOREVER-C2 experiment, pre-test calculations for the forthcoming experiments areperformed. Taking into account both - experimental and numerical results - gives a good opportunity to improve the simulationand understanding of real accident scenarios. After analysing the calculations, it seems to be advantageous to introduce a vesselsupport which can unburden the vessel from a part of the mechanical load and, therefore, avoid the vessel failure or at leastprolong the time to failure. This can be a possible accident mitigation strategy. Additionally, it is possible to install an absolutelypassive automatic control device to initiate the flooding of the reactor pit to ensure external vessel cooling in the event of a coremelt down.