Analysis of two-phase flow phenomena with FLUENT-4 code in the experiments for advanced light water reactor safety
- VTT- Processes, P.O. Box 1604, FIN-02044 VTT (Finland)
In the development of advanced light water reactors, thermohydraulic phenomena are versatile in comparison with the present concepts. The new features are the passive safety systems, where energy transport takes place by natural circulation instead of forced flow. For cooling of the molten core, new concepts have been created including external vessel cooling and core catchers. In all new concepts, two-phase flow circulation patterns exist. The calculational tools should be capable of analysing multidimensional circulation created by the gravity field instead of the forced pump circulation. In spite of extensive model development for the one-dimensional Eulerian solutions for two-phase flow, multidimensional calculation is still a great challenge. The momentum transfer terms and turbulence models for the two-phase flow still require large efforts, although the turbulence models for the single phase flow are versatile and rather advanced at present. Two-phase models exist already now in several CFD codes. In VTT, most experience has been achieved with Fluent-4 Fluent-5 and at last Fluent-6 codes. Fluent-4 and Fluent-6 have the Euler-Euler solution for two-phase conservation equations, which is required for the flow conditions, where the volume fraction of both liquid and gas phases is important and the flow circulation is largely created by the gravity field. VTT is participating in several experimental projects on ALWRs, where multidimensional two-phase circulation is essential. This paper presents three examples of the use of CFD codes for analyses of ALWRs. The first example is connected with SWR 1000 reactor form Framatome ANP. Framatome ANP is performing experiments for evaluation of external cooling of the Reactor Pressure Vessel (RPV) of SWR 1000. The experiments are aimed for determining the limits to avoid critical heat fluxes (CHFs). The experimental programme is carried out in three steps. The first part, the air-water experiments, has been analysed at VTT using Fluent-4.5.2. The code parameters were selected to match the velocity profiles measured by the LDA (Laser-Doppler Anemometer) method, the average void fraction measured by the impedance probes and void fraction profile by the fiber optic probe. The second example is dealing with the BWR90+ concept from Westinghouse Atom. In BWR90+, a conical, downward directed core catcher structure will collect the molten core if it penetrates through the RPV bottom. The core catcher is cooled from outside by surrounding water pool. For examining the cooling of the core catcher structure, an experimental facility has been set up at the Lappeenranta University of Technology in Finland. In the test rig, boiling phenomena on the catcher wall has been studied. The cooling of the core catcher was simulated with Fluent code. In the first phase, one-phase flow situation was studied. The next step, two-phase flow analyses, are in progress. As the third example, the possibilities to model the isolation condenser in the BWR 90+- concept will be discussed. (authors)
- Research Organization:
- American Nuclear Society, 555 North Kensington Avenue, La Grange Park, IL 60526 (United States)
- OSTI ID:
- 21167847
- Resource Relation:
- Conference: ICAPP'02: 2002 International congress on advances in nuclear power plants, Hollywood, FL (United States), 9-13 Jun 2002; Other Information: Country of input: France; 3 refs
- Country of Publication:
- United States
- Language:
- English
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