Numerical approach on the performance prediction of a gas–liquid separator for TMSR

In this paper, the numerical simulation for the gas–liquid flow in a separator applied in the fission gas removal system for thorium molten salt reactor was investigated. The numerical model was established in the frame of Eulerian–Eulerian approach, in which the modeling of the forces acting on the bubbles was introduced. Based on the model, numerical simulations with three flow rates were carried out. Three key parameters (the pressure loss, the separation length, the liquid entrainment ratio) concerned with the separation performance were compared between the numerical results and the experimental data, the results indicate that the calculated results agree well with the experimental data. Hence, the numerical approach shows a promising tool for the performance prediction and the optimization of the gas–liquid separator.     

Structural studies of the phase separation in the UO2–PuO2–Pu2O3 ternary system

In the oxygen hypo-stoichiometric range of (U_1?yPu_y)O_2?x mixed oxide MOX fuels, the U–Pu–O phase diagram is known to exhibit a large biphasic domain depending on the Pu content. However, the phase equilibria are still to be fully described as various representations are proposed in the literature.In the present work, we notify new insights into the phase separation occurring in the UO₂–PuO₂–Pu₂O₃ domain at room temperature. Our microstructural and X-ray diffraction results are compared to the different representations reported in the literature. We provide, for the first time in the hypo-stoichiometric domain, an indisputable experimental observation of a triphasic region at high Pu content, composed of two fluorite-type structures and of one α-Pu₂O₃ sesquioxyde type structure. These results are in contradiction with previous experimental representations of the U–Pu–O ternary system.     

Numerical simulation of gas–liquid–solid three-phase flow using particle methods

We want to simulate, based on particle methods, the dynamic behavior of multi-phase flows in a gas–solid–liquid mixture system. With the governing equations discretized within the finite volume particle method, the effects of contact and collision between solid particles were modeled by the distinct element method. Applicability of the viscosity model and an empirical drag force model were confirmed for the hydrodynamic interactions between solid particles and fluid. Simulations were performed of a single bubble rising in a tank of stagnant solid particle–liquid. The results for the dynamic behavior indicate that the present computational framework of particle-based simulation method may be useful for numerical simulations of multi-phase flow behavior in a solid particle–fluid mixture system.     

Engineering-scale test on the thermal–hydro–mechanical behaviors in the clay barrier of a HLW repository

The thermo–hydro–mechanical (T–H–M) behaviors of a clay barrier are of importance from a performance and safety viewpoint of the engineered barrier system (EBS) for a high-level waste (HLW) repository. An engineering-scale test was carried out to investigate the T–H–M behaviors in the buffer of the Korean reference disposal system (KRS). The test started on May 31, 2005 and is still in operation. The experimental data obtained allowed a preliminary and qualitative interpretation of the T–H–M behavior in bentonite blocks. The temperature was higher as it became closer to the heater, while it became lower as it was farther away from the heater. The water content had a higher value in the part close to the hydration surface than that in the heater part. The relative humidity data suggested that a hydration of the bentonite blocks might occur by different drying–wetting processes, depending on their position. The total pressure was continuously increased by the evolution of the saturation front in the bentonite blocks and thereby the swelling pressure. There was also a contribution of the thermal expansion of the bentonite blocks near the heater and the capillary force in the dry bentonite blocks which the water did not reach from the hydration surface.     

Investigating the performance of a Rh metal catalyst in hydrogen–deuterium exchange reactions in methane for application in low-temperature membrane separators

The development of safe, efficient, and cost effective methods to recover waste components of deuterium–tritium (D–T) plasma reactors, including hydrogen and methane, has attracted much interest in the scientific community. Typically, membrane separators are used for this process, although several problems occur when performing separations at higher temperatures. The application of noble metal catalysts may improve the reaction dynamics and allow the separation process to occur at lower temperatures. In this paper, a series of noble metal catalysts were prepared by a traditional dipping method. Based on an analysis of catalytic performance, the Rh/Al₂O₃ catalyst was determined to be the most suitable for the exchange of hydrogen and deuterium in methane. The catalyst was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and temperature programmed reduction analyses. The effects of the metal loading and experimental conditions were also investigated.     

Elastic–plastic analysis of the steel-to-tungsten transition joint for a high performance divertor

The use of tungsten as a plasma-facing material necessitates a transition joint to the oxide dispersion strengthened (ODS) steel or ferritic steel (FS) structural material of the primary coolant loop at the end of the divertor target plate where the surface heat flux is very low. A critical issue in the transition joints is the coefficient of thermal expansion (CTE) mismatch between the tungsten (or tungsten-alloy) and ODS steel, which can lead to unacceptably high thermal stresses during steady state and ratcheting during cyclic loads. Detailed 2D and 3D thermo-mechanical analyses were conducted to study the behavior of a transition from tungsten to FS with an intermediate layer of tantalum, located outside of the high heat flux region. The results include plastic strains under various loading conditions including fabrication processes, warm and cold shutdown, and allow for plastic behaviors leading to stress relaxation. The accumulation of plastic deformation may cause ratcheting. Modifications were proposed to the transition joint design in order to eliminate stress concentration and ratcheting under cyclic loading. The results of the modified design exhibited less plastic deformation in the joints as well as no ratcheting caused by warm and cold shutdown.     

Numerical study on sodium–water reaction mechanism in the gas phase using counter-flow reaction region

Sodium water reaction (SWR) is a design basis accident of a sodium-cooled fast reactor (SFR). In a steam generator of the SFR, when a heat transfer tube fails, highly pressurized water and/or water vapor will leak into liquid sodium resulting in a chemical reaction between sodium and water or water vapor. In the previous works, mechanisms of the SWR have been researched on surface reaction and gas-phase reaction. The mechanisms, however, are complicated and have not been fully elucidated. The authors have developed a numerical code in which chemical reaction models of sodium and water vapor are coupled with thermal-hydraulics. Experiments of a counter-flow diffusion flame for the gas-phase reaction have also been carried out. In this article, the authors perform numerical simulations based on the experimental conditions to validate two chemical reaction models, the chemical equilibrium model and the Arrhenius model. With respect to the reaction products, the latter model gives more realistic results. In addition, sensitivity analyses are performed for various hydration numbers and main-flow velocities. It is founded that hydration reaction occurs somewhat in the gas-phase reaction and that influences of the main-flow velocity are not negligible mainly from the viewpoint of the reaction surface location.     

Study on the performance of a large-size Cs I detector for high energy γ-rays

The measurement of high-energy γ-rays is an important experimental method to study the giant resonance in a nucleus, c reaction in nuclear astrophysics, and so on. The performance of a large-size Cs I detector for crays detection is studied by comparison between the experimental measurements and GEANT4 simulation. The reliability of the simulated efficiency for low-energy γ-rays is verified by comparing with the experimental data. The efficiency of the Cs I detector for high-energy γ-rays was obtained by the GEANT4 simulation. The simulation shows that the detection efficiency of 20 Me V γ-rays can reach 3.8%.     

Theoretical investigation on the steady-state natural circulation characteristics of a new type of pressurized water reactor

1 Introduction With respect to the inherent safety of nuclear re- actors, application of passive systems/components including natural circulation phenomena as the main mechanism is intended to simplify the safety-related systems and to improve their reliability, to reduce the effect of human errors and equipment failures, and to provide more time to enable the operators to prevent or mitigate serious accidents. Natural circulation is the main mode of heat removal for removing decay heat from t…     

CFD analysis of the loss coefficient for a 90° bend in rolling motion

The local loss coefficient for a 90° bend in rolling motion is investigated with CFD code FLUENT. The calculation results are validated with experimental and theoretical results in steady state. The effect of spanwise and transverse additional forces on the bend loss is significant. The effects of additional forces on the bend loss are mainly embodied in the downstream section. The oscillation of bend loss caused by the spanwise and transverse additional forces is very regular while that caused by velocity oscillation is very irregular. The effect of velocity oscillation on the bend loss is significant in rolling motion with low Reynolds number. But the variation of bend loss coefficient with velocity oscillating period is very limited.     

Research on the steam–gas pressurizer model with Relap5 code

Steam–gas pressurizers are self-pressurizing, and since steam and noncondensable gas are used to sustain their pressure, they experience very complicated thermal–hydraulic phenomena owing to the presence of the latter. A steam–gas pressurizer model was developed using Relap5 code to investigate such a pressurizer's thermal–hydraulic characteristics.The important thermal–hydraulic processes occurring in the pressurizer model include bulk flashing, rainout, wall condensation with noncondensable gas, and interfacial heat and mass transfer. The pressurizer model was verified using results from insurge experiments performed at the Massachusetts Institute of Technology. It was found that noncondensable gas was one of the important factors governing the pressure response, and the accuracy of the developed model would change with different mass fractions and types of noncondensable gas.     

Effect of metal ions in a heated nitric acid solution on the corrosion behavior of a titanium–5% tantalum alloy in the hot nitric acid condensate

For evaluating the application of titanium and its alloys as components of equipment for storing nitric acid condensate in spent nuclear fuel reprocessing plants, the corrosion behavior of titanium–5% tantalum alloy (Ti–5Ta) in a continuously renewed hot nitric acid condensate, and particularly the effect of metal ions in the heated nitric acid solution, was investigated. Corrosion experiments in an apparatus designed to renew the condensate at regular intervals showed that the corrosion rate of Ti–5Ta in the condensate increased linearly with the nitric acid concentration. The surface morphology of Ti–5Ta coupons after the corrosion experiments indicated uniform corrosion under any condition. The oxide film on the coupons had nearly constant thickness, and it was composed of mainly lower Ti oxides, such as TiO and Ti₂O₃, regardless of the nitric acid concentration in the condensate. The experimental results also showed that the addition of metal ions into the heated nitric acid solution increased the nitric acid concentration in the condensate, which resulted in a higher corrosion rate of Ti–5Ta. The corrosion rate increased noticeably as the valence of the metal ion increased and its ionic radius decreased. This effect of metal ions in the heated nitric acid solution on the corrosion rate of Ti–5Ta in the condensate was evaluated quantitatively based on the Gibbs free energy of hydration of the metal ions, and the calculated corrosion rates of Ti–5Ta in the condensate were found to be in good agreement with the experimental values.     

Characterization of a new shielding rubber for use in neutron–gamma mixed fields

A variety of formulations was investigated for the fabrication of an appropriate shielding rubber to be used in neutron–gamma mixed fields. Having considered the required mechanical properties together with tungsten as the gamma-ray absorbing element, calculations with MCNPX 2.6 code confirmed that the incorporation of 5 weight percentage(wt%) of boron carbide exhibited the best performance as a thermal neutron absorber. A series of both experimental and simulation results are provided for comparison.     

Influence of the position relationship between gas–liquid interface and laser focus on plasma evolution characteristics in jet LIBS technology

In order to understand the characteristics of breakdown process, plasma evolution and spectral emission in liquid jets laser-induced breakdown spectroscopy methods under the influence of the position variation between laser focus and gas–liquid interface, this work takes the plasma generated by laser-induced liquid jets as the object of study and discusses the changes in the spatial and temporal evolution characteristics and spectral radiation of the plasma when the position parameters between t...     

An optimized numerical method to pre-researching the performance of solid-phase oxygen control in a non-isothermal lead–bismuth eutectic loop

In the present work, a new transient calculation method for parameters that can be used to evaluate the ability of oxygen control in a non-isothermal lead-bismuth eutectic(LBE) loop with solid-phase oxygen control was proposed. It incorporates the dissolution process of PbO particles and the oxygen mass transfer process, and an optimized method was used for finding out the optimized oxygen mass transfer coefficient. In numerical terms, three mass transfer models were simultaneously applied, and ...     

An optimized numerical method to pre-researching the performance of solid-phase oxygen control in a non-isothermal lead–bismuth eutectic loop

In the present work, a new transient calculation method for parameters that can be used to evaluate the ability of oxygen control in a non-isothermal lead-bismuth eutectic(LBE) loop with solid-phase oxygen control was proposed. It incorporates the dissolution process of PbO particles and the oxygen mass transfer process, and an optimized method was used for finding out the optimized oxygen mass transfer coefficient. In numerical terms, three mass transfer models were simultaneously applied, and ...     

Influence of vacuoles with gas–liquid inclusions on the thermobaric destruction conditions of natural quartz under dynamic heating in an RF-TICP torch system

In the present work, the turbulent mixing process of a polydisperse quartz particle flow with a plasma stream generated by a radio-frequency(RF) inductively coupled plasma torch was numerically studied. The thermobaric stress in the quartz particles under dynamic heating in a heterogeneous plasma flow was determined by a two-stage approximation approach. The effect of the presence of vacuoles in natural quartz on the particle thermobaric destruction conditions was studied. It was found that the ...     

A SANS investigation of the irradiation-enhanced α–α′ phases separation in 7–12 Cr martensitic steels

Five reduced activation (RA) and four conventional martensitic steels, with chromium contents ranging from 7 to 12 wt%, were investigated by small angle neutron scattering (SANS) under magnetic field after neutron irradiation (0.7–2.9 dpa between 250 and 400 °C). It was shown that when the Cr content of the b.c.c. ferritic matrix is larger than a critical threshold value (∼7.2 at.% at 325 °C), the ferrite separates under neutron irradiation into two isomorphous phases, Fe-rich (α) and Cr-rich (α^′). The kinetics of phase separation are much faster than under thermal aging. The quantity of precipitated α^′ phase increases with the Cr content, the irradiation dose, and as the irradiation temperature is reduced. The influence of Ta and W added to the RA steels seems negligible. Cold-work pre-treatment increases slightly the coarsening of irradiation-induced precipitates in the 9Cr–1Mo (EM10) steel. In the case of the low Cr content F82H steel irradiated 2.9 dpa at 325 °C, where α^′ phase does not form, a small irradiation-induced SANS intensity is detected, which is probably due to point defect clusters. The α^′ precipitates contribute significantly to the irradiation-induced hardening of 9–12 wt% Cr content steels.