ICONE11-36306 CONTROLLING THE MOISTURE CONTENT IN THE STEAM BY USING NOZZLES IN BWR'S

概要

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The subject of this work is to show a new method based on well verified CFD code for the particular purpose of moisture reduction in BWR's for low leakage loading. A complete 3D-steady state is generated for a vessel region starting with the pump entrance, going through the lower head, core upper mixing chamber and the stand pipes. The flow parameters at the stand pipes outlets are then used as a input for a empirical model for analysis of the cyclones and dryers performance. The empirical model is based on appropriate experimental data base. The parameters at the exit of the dryers are then cross section averaged in order to obtain the final moisture at the vessel exit. Comparing two specific BWR fuel cycle states for low leakage loading we find out that a reduction of about 40% of the peripheral mass flow leads to : (a) Effective reduction the moisture content in the fresh steam ; (b) The averaged void over the core is slightly increased over the first half of the fuel cycle and remains almost unchanged over the end of the fuel cycle which is positive for the fuel utilization ; (c) The reduced mass flow amount over the periphery is pushed through the remaining central part of the core which increases the safety margins for the most loaded bundle. The method is already in use for performance optimization of existing plants and for design of a new plants.
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