Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf
Coupled Thermal Structural Analysis of LWR Vessel Creep Failure Experiments
Willschütz, H.-G.; Altstadt, E.; Sehgal, B. R.; Weiß, F.-P.
Considering the hypothetical core melt down scenario for a Light Water Reactor the behaviour of the Reactor Pressure Vessel during the late phase of the accident has to be investigated. The FOREVER-experiments, currently underway, are simulating the lower head under the load of a melt pool with internal heat sources. Due to the multi-axial creep deformation of the vessel with a non-uniform temperature field these experiments are an excellent possibility to validate numerical creep models. Therefore a Finite Element model is developed on the basis of a commercial multi-purpose code. Using the CFD module the temperature field within the vessel wall is evaluated. The transient structural mechanical calculations are performed using a new numerical approach which avoids the use of a single creep law with constants evaluated for a limited stress and temperature range. Instead of this a three-dimensional array is developed where the creep strain rate is evaluated according to the actual total strain, temperature and equivalent stress. Performing post-test calculations it was found that the assessment of the experimental data and of the numerical results has to be done very carefully. Considering the experiment FOREVER-C2, for example, the recorded creep process appears to be tertiary, if a constant temperature field is assumed. But slight temperature changes during the creep deformation stage could explain the observed creep behaviour, too. Taking into account both - experimental and numerical results - gives a good opportunity to improve the simulation and understanding of real accident scenarios.
Keywords: Finite Element Calculations; FOREVER-Experiment; Coupling of Thermo-Fluid dynamic and Structural Mechanical Model; Advanced Creep Modelling
- Nuclear Engineering and Design, Elsevier, 208 (2001)265-282