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Sodium combustion oxide aerosols are the main carriers of radioactive materials in a sodium-cooled fast reactor (SFR) during sodium fire accidents. Therefore, it is of great significance to simulate aerosol behavior in sodium pool fires to evaluate radioactive source terms in the containment or environment. In this work, a numerical method has been developed to simulate sodium oxide aerosol behavior during sodium pool fires. The Classical Nucleation Theory has been taken into account to simulate gas-to-particle conversion (GPC). The model has been evaluated theoretically in 280 cases with three main parameters: sodium pool temperature, pool diameter, and oxygen concentration. The correlation established by fitting data points is associated with the sodium evaporation rate. The SFA code has been developed based on advanced sodium pool combustion and aerosol models coupled with GPC correlations. In comparison with the experimental data, the code-calculated average atmospheric temperature, airborne aerosol concentration, and particle size are in good agreement with the data, which indicate that the method is reliable and can be applied in code development in the future. [ABSTRACT FROM AUTHOR]

A transportable fluoride-salt-cooled high-temperature reactor (TFHR) design with 20-MW(thermal) rated power and 18-month fuel cycle is proposed for off-grid applications. One of the design goals of the compact reactor core is potential transport by truck, rail, or air. Full-core thermal-hydraulic analyses and improvements using three-dimensional computational fluid dynamics (CFD) were performed previously to demonstrate the feasibility of a TFHR design at a nominal power of 20 MW(thermal). In this paper, the best-estimate system code Reactor Excursion Leak Analysis Program (RELAP5-3D) is adopted to study the transient behavior of this TFHR design and the safety characteristics of the primary loop system during accident conditions. The modeling results of the steady state were verified using CFD results with consideration of radial heat conduction between heat transfer unit cells. Four most challenging accidents of anticipated transient without scram were analyzed, as well as parametric studies of some key factors. These accidents include unprotected reactivity insertion accident (URIA), unprotected loss of heat sink (ULOHS), unprotected loss of flow (ULOF), and a combination accident of ULOF and ULOHS. The results indicate that transient temperature limits are not exceeded during the most severe accidents. They indicate satisfactory transient performance of the TFHR design. The transient temperature limit of structure material Hastelloy N, based on embrittlement phenomena, poses the most limiting constraint due to the small temperature margin of about 20 K in the accident combination of ULOF and ULOHS. Overall, TFHR is a sound reactor design from a thermal-hydraulic viewpoint. [ABSTRACT FROM PUBLISHER]

AbstractInteraction of prevailing ocean waves and wind with the platforms containing the small modular reactors (SMRs) employed in marine environments may significantly alter the flow and friction characteristics inside these reactors. The present research is focused on the numerical study of the effects of rolling motions on the turbulent flow and frictional characteristics of a three-dimensional closed loop of narrow rectangular channels using Ansys Fluent. The computational results have been corroborated with experimental data present in literature. The results illustrate that flow and friction characteristics fluctuate sinusoidally as the loop undergoes rolling motion. Strong fluctuations were observed in the flow rate and time-dependent friction coefficient with an increase in rolling amplitude or reduction in the rolling period. These variations became more pronounced at low Reynolds numbers and diminished at higher Reynolds numbers. Increasing the fluid viscosity also subsided the rolling effects. The average flow velocity in the loop was found to decrease from 0.27 to 0.15 m/s in various phases of the rolling period. The relative Reynolds number was found to be reduced by 50% under rolling motions for the range of steady-state Reynolds numbers investigated in the present study. The transient friction coefficient was also found to oscillate under rolling motion with the same period as that of excitation. The transient friction coefficient’s oscillations also increased with rolling amplitude or reduction in the rolling period. However, the temporally averaged friction coefficient under rolling motions was found to be equal to the steady-state frictional coefficient in the loop. [ABSTRACT FROM AUTHOR]