Post-Test Calculations of Medium Scaled Pressure Vessel Creep Failure Experiments


Post-Test Calculations of Medium Scaled Pressure Vessel Creep Failure Experiments

Willschütz, H.-G.; Altstadt, E.; Weiss, F.-P.; Sehgal, B. R.

For the calculation of experiments simulating the behavior of the lower head in a core melt down scenario like FOREVER (performed at the Royal Institute of Technology, Stockholm) it is necessary to model the melt pool convection and the temperature field within the vessel as well as creep and plasticity processes. Therefore a 2D Finite Element Model is developed based on the code ANSYS®. The CFD module is used to calculate the thermodynamics. The resulting temperature field of the vessel wall is applied to the mechanical model. To describe the visco-plastic deformation a numerical creep data base (CDB) is developed where the creep strain rate is evaluated in dependence on the current total strain, temperature and equivalent stress. In this way the use of a single creep law, which employs constants derived from the data for a limited stress and temperature range, is avoided. For an evaluation of the failure times a damage model according to an approach of Lemaitre is applied.
After post-test calculations for the FOREVER-C2 experiment, pre-test calculations for the forthcoming experiments are performed. Taking into account both - experimental and numerical results - gives a good opportunity to improve the simulation and understanding of real accident scenarios. After analyzing the results of the calculations, it seems to be advantageous to provide a vessel support, which can unburden the vessel from a part of the mechanical load and, therefore, avoid the vessel failure or at least prolong the time to failure. This can be a possible accident mitigation strategy. Additionally, it may be advantageous to install a passive automatic control device to initiate the flooding of the reactor pit to ensure external vessel cooling in the event of a core melt down.

Keywords: core melt down accident; lower head behavior of the RPV; Finite Element Method; creep and damage modeling

  • Lecture (Conference)
    2003 International Congress on Advances in Nuclear Power Plants ICAPP '03 May 4-7, 2003; Congress Palais, Córdoba, SPAIN, Proceedings on CD
  • Contribution to proceedings
    2003 International Congress on Advances in Nuclear Power Plants ICAPP '03 May 4-7, 2003; Congress Palais, Córdoba, SPAIN, Proceedings on CD

Permalink: https://www.hzdr.de/publications/Publ-5196
Publ.-Id: 5196