Abstract
For the validation of advanced two-fluid CFD models at boiling water reactor (BWR) conditions, it is necessary to have good experimental data challenging for the code by reflecting relevant flow phenomena. The present experimental study aims to provide detailed film thickness distributions in a BWR-like subchannel geometry, including spacer grids and heat transfer. This is achieved using chloroform as a working fluid, indirectly heated by hot water channels simulating BWR fuel rods. X-ray equipment was used to produce tomographic 3D-data of time-averaged attenuation coefficients which essentially represent the liquid holdup. The conversion to film thickness was done by integrating the attenuation coefficient along lines perpendicular to the rod wall and using an effective chloroform attenuation coefficient determined by numerical simulation of the experimental setup, including X-ray sensor behavior. The simulation method was validated by using two different sensors types. Measurements were performed over the whole cross-section of the channel and an axial length of 11 cm. The experiments cover a range of liquid flow rates in the pre- and post-dryout regime.
Highlights
Boiling water reactors (BWR) are a common reactor type for elec tricity generation and produce almost 20% of the electricity of all re actors worldwide (International Atomic Energy Agency IAEA, 2018)
The highest two flow rates are again quite close together. The reason for this behavior is not Tomographic imaging was used to measure the 3D attenuation co efficients over an 11 cm length of a heated flow loop test section, including a spacer grid, in a simplified boiling water reactor (BWR)-like subchannel geometry, using an X-ray tube and a flat panel detector
Approaching dryout, no qualitative changes in film thickness could be observed until a final sudden breakdown of the liquid film happens at the entire heated sur face at once
Summary
Boiling water reactors (BWR) are a common reactor type for elec tricity generation and produce almost 20% of the electricity of all re actors worldwide (International Atomic Energy Agency IAEA, 2018). Water enters the core from below at slightly subcooled conditions is heated and partly evaporates, resulting in annular flow for most of the height of the reactor core. The understanding of annular flow plays an important role for safe and economic operation of a BWR. It is desirable to go to higher power. How ever, this simultaneously decreases the margin to dryout of the liquid film. Dryout could result in an increase of cladding temperature, potentially endangering the integrity of the fuel cladding
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