Gwang Hyeok Seo

Numerical analysis of RBHT reflood experiments using MARS 1D and 3D modules

The Rod Bundle Heat Transfer (RBHT) program was performed experimentally to analyze the reflood heat transfer phenomena under the conditions of reflood phase following a hypothesized loss of coolant accident (LOCA) by the team of Penn State University. In order to verify the experimental data using a numerical analysis, the Multi-dimensional Analysis of Reactor Safety (MARS) assessment of the RBHT experimental data was carried out for the flooding rates of 0.0254 and 0.1524 m/sec with the upper plenum pressure of 276 kPa. The RBHT experimental data of Tests 1285 and 1383 were compared with the calculation results of the MARS 1D and 3D modules. The MARS code shows a good agreement in the general trend of the peak cladding temperatures although there are limitations in predicting accurate quenching time for both modules. However, in comparison to the MARS 1D module simulation, the MARS 3D module shows the improved calculation capability in that the code can capture local enhanced heat transfer with implication of spacer grids. Moreover, the temperature profiles simulated by the 3D module show the accurate prediction at which the local peak temperatures occur. For more enhanced simulations, local flow parameters such as cross flow and vortex flow need to be analyzed for a more accurate prediction of quenching behavior.

Numerical evaluation of SmCo permanent magnet flowmeter measuring sodium flow in a low flow rate regime using FLUENT/MHD module

One of the several key subsystems in the test facility of Korean sodium-cooled fast reactor is a plugging meter system, which measures the impurities in the sodium using an indirect online technique. To measure the low flow rate, a permanent magnet flowmeter was developed owing to its inherent fast response time, non-invasive characteristic, relatively accurate flow rate measurements, and excellent linearity between the flow rate and flowmeter signal. However, several limitations have been reported in the experimental evaluation of the flowmeter under low flow rate conditions given the measurement capability of the current experimental facility. Thus, the performance of the flowmeter was evaluated numerically using a commercial computational fluid dynamics tool, a FLUENT/MHD module, based on the finite volume method with the help of electromagnetic analysis software, ANSYS MAXWELL. The FLUENT/MHD module was validated by comparing the simulation results with the experimental results. The relative error of the FLUENT simulation was estimated to be approximately 0.24% compared with the experimental results. After the validation process, MHD simulations were conducted to calculate the flowmeter voltage signals versus flow rates, especially in a low flow rate regime, where the linearity between the flow rate and flowmeter signal was carefully analyzed.