Institute of Nuclear Technology and Energy Systems (IKE), University of Stuttgart (Germany)
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The accident management in a generic nuclear power plant containment with a convection flow of high-temparature gases is simulated. An activated spray mixes the turbulent flow and inhibits the formation of a possibly explosive upper region filled with hydrogen. Condensation of the steam is promoted and the maximum pressure, which may also endanger the containment integrity, is limited.
A postulated accident scenario of a nuclear power plant is a leak in the primary circuit, possibly resulting in steam, hydrogen and radioactive aerosols in the beforehand air-filled reactor containment building. Within the initial phase of the present project, the complex fluid dynamics of the relevant buoyancy-driven gas flows had been simulated, including turbulent mixing and the film condensation of steam at the cool walls. Condensation also occurs in the form of a droplet phase within the interior bulk volume of the containment.
The aerodynamic two-fluid model, in which both gas and the dispersed liquid are modelled as interpenetrating continua, has been applied using the computational fluid dynamics code ANSYS CFX. In the final project stage, our own additional physical models have been implemented and validated by comparison to physical experiments in the THAI model containment, e.g. the wash-out of aerosols by a water spray coming from a top-mounted nozzle as shown in figure 1. This spray of droplets mixes actively the various gas components and is able to prevent the formation of a possibly explosive upper region filled with hydrogen. Additionally, bulk condensation of the steam is promoted and therefore the maximum pressure, which may endanger the containment integrity, is limited.
In order to demonstrate the thermal hydraulics in a containment during the temporal evolution of a severe accident, a three-dimensional geometry of a model containment was generated based on a German pressurized water reactor including free bulk volumes and concrete or metallic structures. In the first project stages, about 10 million gridpoints have been used on the CRAY XE6 (Hermit). With the installation of the CRAY XC40 (Hazel Hen), we were able to investigate systematically the numerical accuracy and possible uncertainty associated with the meshing and discretization, even for such complex two-phase flows on very large meshes. For this, time-dependent computations were performed with up to 140 million gridpoints on up to 1500 computational cores and the Grid-Convergence Index (GCI) was computed as a measure for grid convergence.
The GCI-investigation shows, that the numerical error can be kept below the model uncertainty for practical simulations only if high-performance computers are available. The initial stage of the temporal development in a postulated accident scenario can be simulated by safety engineers in order to support the safe design and operation of nuclear power plants.
This work was supported by the German Federal Ministry of Economic Affairs and Energy (BMWi) on the basis of a decision by the German Bundestag, with project numbers 1501414 and 1501493. The simulations were performed at HLRS under the grant number TurboCon/12843.
Christian Kaltenbach, Eckart Laurien (PI), Abdennaceur Mansour, Jing Zhang
Prof. Dr.-Ing. Eckart Laurien
Institute of Nuclear Technology and Energy Systems (IKE), University of Stuttgart
Pfaffenwaldring 31, D-70569 Stuttgart (Germany)
E-mail: eckart.laurien [@] ike.uni-stuttgart.de
HLRS project ID: TurboCon3