Abstract
This paper reports on the modeling and simulation of flashing-induced instabilities in naturalcirculation systems, with special emphasis on simplified boiling water reactors (SBWRs). In this work, flashing-induced oscillations have been studied by using an experimental test facility (SIRIUS-N) and RELAP5/MOD3.2 thermal hydraulic code. The behavior of the test facility is investigated for different values of core inlet temperature value. The results of the simulations have been compared qualitatively and quantitatively with experiments. In general, deviations are found between the numerical and experimental results, in spite of the close similarity between the SIRIUS-N facility and the definition of the system in the RELAP code. This result indicates that predictions regarding experimental facility, based on modeled system, should be carefully considered.
Highlights
In a boiling natural circulation loop like simplified boiling water reactors (SBWRs), a fairly long chimney is installed on the core to increase theThe Central Research Institute of Electric Power Industry (CRIEPI) in Japan has constructed a low-pressure thermo hydraulic test facility to study the start-up stability of the Simplified Boiling Water Reactor [4]
The experimental facility is modeled by using the RELAP5/MOD3.2 computer code and the predictions of thermal hydraulic code are compared with the experimental results
This study has focused on the investigation of the flashing induced instabilities, which are very likely to occur during the low pressure start-up phase of SBWRs
Summary
In a boiling natural circulation loop like SBWR, a fairly long chimney is installed on the core to increase the. Andersen et al (1995) reproduced flashing-induced instabilities with TRACG and gained some promising qualitative agreement with the different types of flow oscillations obtained experimentally at CRIEPI test facility. Furuya et al (2005) presented some Stability maps which were obtained in reference to the inlet subcooling and the heat flux at the system pressure They show that by increasing the inlet temperature, four main types of behavior can be observed. For numerical simulation of two phase flow instabilities, a 6-equation model can be used, where the two phases are treated as two separated fluids for which mass, momentum and energy balances are solved separately This type of model is implemented in some of the system codes (RELAP5, ATHLET, TRAC, MONA) and allows thermal non-equilibrium and slip to be taken into consideration between the phases. The simulation results have been compared with the experiments that were carried out, within the framework of the CRIEPI project, on the SIRIUS-N facility [4]
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