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See detailInvestigation of condensation process inside inclined tube
Zhang, Yu UL

Doctoral thesis (2020)

Generation III+ reactor designs partially rely on passive safety systems. It aims to increase the plant safety standards and to reduce investment costs. Passive Decay Heat Removal Systems, such as the ... [more ▼]

Generation III+ reactor designs partially rely on passive safety systems. It aims to increase the plant safety standards and to reduce investment costs. Passive Decay Heat Removal Systems, such as the Emergency Condenser (EC) of the KERENA reactor design, plays an important role in the safety in nuclear power plants. As part of the emergency cooling chain, EC removes the decay heat from the reactor pressure vessel and transfers it to the flooding pool. For the successful design of the EC, the reliable prediction of the condensation heat transfer inside inclined pipes is one of the important factors. One-dimensional (1D) codes, such as ATHLET, RELAP and TRACE, are widely used today by engineers to predict the thermal hydraulic behavior of the system in nuclear power plant. However, state-of-the-art 1D codes are mainly validated for active components, and the qualification of passive systems is still a remaining problem. The goal of this thesis therefore is to investigate the condensation phenomena in EC using current advanced 1D code ATHLET (Analysis of Thermal-hydraulics of Leaks and Transients). The performance of ATHLET for prediction of condensation in slightly inclined tube was assessed and the results showed that the standard models in ATHLET code have significant deficiencies on the prediction of the condensation heat transfer coefficients. Thus, the new empirical model has been derived using experimental data from COSMEA (COndenSation test rig for flow Morphology and hEAt transfer studies) tests, condensation experiments for flow morphology and heat transfer studies in a single slightly inclined tube conducted by HZDR (Helmholtz-Zentrum Dresden-Rossendorf) and data sourced from literature. The new model was developed using Machine Learning – Regression Analysis methodology in MATLAB, which consists of upper liquid film condensation and bottom convective condensation. It was further implemented in ATHLET with Python programming language and the modified ATHLET code was used to calculate the COSMEA experiments. The post-calculation results were compared to experiments in three aspects: heat flux, condensation rate and void fraction along the whole pipe. The outcomes showed that the modified ATHLET code can be used to recalculate the relevant heat transfer values of experiments under different pressure and mass flow rate conditions. [less ▲]

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See detailAn investigation of condensation process at COSMEA test facility with ATHLET code
Zhang, Yu UL; Geißler, Thomas; Leyer, Stephan UL et al

in Kerntechnik (2018), 83(3), 208-214

Safety is an essential topic in the development process of nuclear power plant. Several Generation III and III+ reactor designs contain passive safety system to control accident without external power. An ... [more ▼]

Safety is an essential topic in the development process of nuclear power plant. Several Generation III and III+ reactor designs contain passive safety system to control accident without external power. An example is the Emergency Condenser (EC) of the KERENA reactor design. The EC removes heat from the Reactor Pressure Vessel in the case of design accidents. The experimental facility COSMEA at Helmhotz Zentrum Dresden Rossendorf (HZDR) was set up to investigate the flow morphology and heat transfer structure of condensation inside a slightly inclined tube. In this paper, the condensation process in COSMEA was simulated with the thermal hydraulic system codes ATHLET. The performance of the ATHLET heat transfer models were identified. The simulation results were compared against the experiments. The heat flux, condensation rate and temperature of cooling water during the condensation was analyzed. [less ▲]

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See detailSimulation of condensation in a inclined tube with ATHLET code
Zhang, Yu UL; Leyer, Stephan UL

Presentation (2017, September 13)

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See detailSIMULATION OF CONDENSATION IN A SLIGHTLY INCLINED TUBE AT COSMEA FACILITY WITH ATHLET CODE
Zhang, Yu UL; Geißler, Thomas; Leyer, Stephan UL et al

Scientific Conference (2017, September 06)

Safety is an essential topic in the development process of nuclear power plant. Several Generation III reactor designs contain passive safety system to control accident without the need for external power ... [more ▼]

Safety is an essential topic in the development process of nuclear power plant. Several Generation III reactor designs contain passive safety system to control accident without the need for external power supply. An example for such passive systems is the Emergency Condenser (EC) of the KERENA reactor design. The system removes heat from the Reactor Pressure Vessel in the case of design basis accidents. The experimental facility COSMEA at Helmhotz Zentrum Dresden Rossendorf (HZDR) was set up to investigate the flow morphology and heat transfer structure of condensation processes. The test rig consists of a 3 m long condenser pipe which is 0.76° inclined with inner diameter 43.3 mm. On the shell side active cooling is performed using the TOPFLOW facility infrastructure. According to the Emergency Condenser Reference design, the experiments of COSMEA are conducted in different pressure levels (5, 15, 25, 45 and 65 bar) with steam mass flow rates up to 1 kg/s. An inlet mixing system was developed to operate the experiment in a stepwise method due to the scale of the test rig. Condensation rates, pressure, temperature and flow rate for different steam fraction are measured. In addition, an x-ray tomography is installed to study the details of the resulting stratified flow structures. Extra heat flux probes are assembled to detect the azimuthal distribution of the heat flux. In this work, COSMEA was simulated the thermal hydraulic system codes ATHLET. The performance of the ATHLET heat transfer models were identified. Primarily, the steady-state model was developed and the simulation results were compared to the experiment. The thermal coupling which considers the heat exchange between outside and inside of the pipe during the condensation was analyzed. Posteriorly the case of modeling transient condensation process was simulated. The influence on thermal coupling parameters, particularly heat transfer coefficient due to pressure drop inside the pipe was predicted and the feasibility and limitation of the system codes were evaluated. [less ▲]

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