Objective
The containment is the last barrier protecting the population and the environment against radioactive consequences of a hypothetical severe accident. Therefore the assurance of its integrity is a key issue. Four aspects of the containment integrity problem are examined: leak assessment, the consequences of hydrogen explosions, the endangering of the containment resulting from impacting missiles and the containment coolability after a severe accident.
The objective of the programme is to reach a well based common position on these subjects.
Particle Deposition in Tubes and Cracks
The gas dynamics equation have been recast into a form suitable for calculating gas flow in non uniform tubes in the laminar and turbulent flow regimes, from low speed up to critical flow conditions. The results of these calculation are compared with an extensive set of experiments and excellent agreement is found. The various deposition processes that particles can undergo on surfaces are examined and given the particle concentration in the tube. This equation is non-linear and integer-differential in nature, and in order to solve it we developed a method which involves prescribing a geometrical plug shape but allowing the parameters within it to be time dependent. Plugging times and the amounts of particulate and gas that have escaped prior to plugging are calculated. Comparison with experiment is made and reasonable agreement found.
Experimental and Theoretical Investigation of Steam Leakage through Concrete Cracks
The introduction in the model implemented in TRIO-EF of the effects of condensation at the wall and the variation of the crack thickness has been done in view of applications in more realistic cases and will be useful to interpret the SIMIBE experiment.
Hydrogen Detonation
Two tests series were performed (3 + 8 tests) with different hydrogen concentrations, initial pressures, and detonation ignition methods (high explosive and accelerating flame). Three tests with relatively good data quality were selected for the initial analysis.
In some tests the initial conditions of the gas mixture are not known with the desired precision, due to technical difficulties in the secondary piping (pumps, filters). Two methods for measuring the hydrogen concentration in the gas mixture did not always agree with the required precision (about +/- 1%). Some of the tests will be repeated in the next measurement campaign.
Code Evaluation
The benchmark led to improvements of all tested codes. In PLEXUS more precise functions for heat capacities and enthalpies led to the good agreement with measured data. The fairly complex reaction model (5 equations) seems to work well, it is however expensive in computing time.
In the two codes DET1D and D3D the important result was improvement of the heat of reaction. A more precise reaction kinetics model is desirable which however should not lower the chemical time step very much. Reduced mechanisms are presently under development.
Work programme
The experimental programme of the leak assessment activity is aiming at the characterisation of the leakage of air/steam mixtures through cracks with rough walls in the SIMIBE facility of CEA-DRN/Saclay. Theoretical methods are developed by ElectroWatt/Horsham for predicting the 2D time-dependent behaviour of gas/vapour/liquid/aerosol mixtures in fine capillaries. Microcrack plugging problems by aerosols are examined by AEA/Winfrith with emphasis on the influence of the pressure drop and the water vapour content in the carrier gas: aerosol deposition, resuspension and saltation phenomena are also investigated. CASTEM 2000 is further used to compute cracking probabilities and concrete deformations. The hydrogen detonation activities, both at CEA Saclay and KfK, are oriented towards the experimental validation of computer tools for the prediction of deflagration-to-detonation transition (DDT) and of detonation effects, with emphasis on the hydrogen chemistry and on the treatment of shock waves in 3-D geometries, using the codes PLEXUS, D3D and DET3D.
The concrete impact activities are oriented towards the experimental validation of numerical models for concrete impact and perforation, with emphasis on non-linear strain-rate effects and failure mode analysis. CEA Saclay is conducting a series of experiments on high resistance reinforced concrete slabs. Blind benchmark computations are performed by the participants for different impact energies.
University of Karlsruhe is developing a new constitutive stress-deformation law and a special "slide" finite element to treat the friction energy produced under high pressure impact conditions during the steel/concrete interaction, using experiments from the Fraunhofer Institute ICT.
In the framework of Decay Heat Removal (DHR) assessments ENEA-ERG/Rome is conducting experiments on the thermo-mechanical cracking behaviour of high-performance concrete at elevated temperatures (100 till 400 C) both in compression and in tension.
Concrete calculations, including strain-rate effects and material behaviour under very high pressure, are also performed by ANPA/Rome using DYNA-2D, with emphasis on structural identification techniques developed at the La Sapienza University of Rome.
Direct Containment Heating (DCH) assessments are being conducted by CEA Saclay on the future MISTRA mock-up and on the RAPSODIE containment, using thermal-hydraulics models like CONTAIN, JERICHO and TRIO for the stratification and thermal-hydraulics problems. Another series of DCH studies are performed by KfK in the PASCO (PASsive containment COling by natural air convection) facility with the aim of reducing the pressure and the temperature in the containment. Moreover the University of Munich is assessing the data base for heat transfer data, generated at the HDR and the Battelle Frankfurt facilities.
Fields of science
Programme(s)
Call for proposal
Data not availableFunding Scheme
CSC - Cost-sharing contractsCoordinator
75015 PARIS
France