An experiment performed in SPARC experimental facility, was simulated with the computational fluid dynamics code OpenFOAM. The experiment took place in two phases. In the first phase, a helium-air layer was generated, which was then eroded with a vertical air jet injected in the vessel axis during the second experimental phase. A three-dimensional and a quasi-two-dimensional numerical models of a cylindrical vessel were developed and mesh convergence studies were performed. The mixing process was simulated as a single-phase flow with common momentum equation. Included gas species mass fractions are considered as passive scalars and are calculated using the transport equation. However, term describing the molecular diffusion cannot be neglected in our case and had to be added to diffusion equation implemented in default OpenFOAM solver. The k-ε turbulence model with additional buoyancy term implemented in OpenFOAM was used for turbulence modelling. Despite improvement of the physical model and following the Best Practice Guidelines, the results obtained with OpenFOAM CFD code still, at some locations, differ substantially from the experimental results. A modified definition of low Reynolds number eddy viscosity correction function is proposed, which significantly improves the agreement between measurements and calculation results.

High fidelity velocity field experimental data in a liquid metal plenum is presented and compared with numerical simulations. While work has already been established for fluids like air and water, research on low Pr fluids (Pr ≪ 1) (e.g. liquid metals) has fewer experimental data sets with validation-quality data. Work in advanced reactors using liquid metal coolant requires validated numerical simulations for safety analyses. The Gallium Thermal-hydraulic Experiment (GaTE) facility is outfitted with acoustic backscattering measurement techniques to generate the high fidelity distributed flow field data in a liquid metal plenum (a 1/20th scale of the Department of Energy’s sodium cooled Advanced Burner Test Reactor design). The high spatial and temporal resolution of the sensors are required to capture the fluctuations of velocity to allow a more direct comparison to the numerical simulations. For these simulations the coupled mass and momentum equations under the large eddy simulation (LES) framework were solved with the wall-adapting local eddy-viscosity (WALE) model for sub-grid scale formulations. Since the temperature transients of interest for reactor safety have a period of about a minute in the GaTE system, there may not be enough time to allow statistical tools to check one-to-one correspondence. So the data collection period for both data sets was extended to allow convergence of the mean and a larger sample size for other statistics during system steady-state, isothermal tests. Two characteristic velocities of the plenum inlet barrel were investigated (U = 40, 60 mm/s; Re = 7,000, 11,000). Probability distributions show good agreement between experiment and simulation with the difference only in the low-probability tails that LES is not expected to simulate. The time averaged mean axial distribution of the vertical velocity also shows good agreement between the two setups.

In recent years, hybrid nanofluids, as a new kind of working fluid, have been widely studied because they possessing better heat transfer performance than single component nanofluids when prepared with proper constituents and proportions. The application of hybrid nanofluids in nuclear power system as a working fluid is an effective way of improving the capability of In-Vessel Retention (IVR) when the reactor is in a severe accident. In order to obtain hybrid nanofluids with excellent heat transfer performance, three kinds of hybrid nanofluids with high thermal conductivity are measured by transient plane source method, and their viscosity and stability are also investigated experimentally. These experimental results are used to evaluate the heat transfer efficiency of hybrid nanofluids. The results show that: (1) The thermal conductivity of hybrid nanofluids increases with increasing temperature and volume concentration. When compared to the base fluid, the thermal conductivity of Al 2 O 3 -CuO/H 2 O, Al 2 O 3 -C/H 2 O and AlN-TiO 2 /H2O nanofluids at 0.25% volume concentration increased by 36%, 24%, and 22%, respectively. (2) Surfactants can improve the stability of hybrid nanofluids. The Zeta potential value is related to the thermal conductivity of the hybrid nanofluids, and it could be used to explain the relationship between the thermal conductivity of the hybrid nanofluids and the dispersion. It also could provide a reference for subsequent screening of high thermal conductivity nanofluids. (3) The addition of C/H 2 O can effectively reduce the dynamic viscosity coefficient of hybrid nanofluids. (4) The analysis of heat transfer efficiency of the hybrid nanofluids found that both Al 2 O 3 -CuO/H 2 O and Al 2 O 3 -C/H 2 O have better heat transfer ability than water under certain mixing conditions. This study is conducive to further optimizing hybrid nanofluids and its application to the In-Vessel Retention in severe reactor accidents.

A Very High Temperature Reactor (VHTR) is one of the next generation nuclear reactor systems. From a view point of safety characteristics, a passive cooling system should be designed as the best way of a reactor vessel cooling system (VCS) in the VHTR. Therefore, the gas cooling system with natural circulation is considered as a candidate for the VCS of the VHTR. Japan Atomic Energy Agency (JAEA) is advancing the technology development of the VHTR and is now pursuing design and development of commercial systems such as the 300MWe gas turbine high temperature reactor GTHTR300C (Gas Turbine High Temperature Reactor 300 for Cogeneration). In the VCS of the GTHTR300C, many rectangular flow channels are formed around the reactor pressure vessel (RPV), and a cooling panel utilizing natural convection of air has been proposed. In order to apply the proposed panel to the VCS of the GTHTR300C, it is necessary to clarify the heat transfer and flow characteristics of the proposed channel in the cooling panel. Thus, we carried out an experiment to investigate heat transfer and fluid flow characteristics by natural convection in a vertical rectangular channel heated on one side. Experiments were also carried out to investigate the heat transfer and fluid flow characteristics by natural convection when a porous material with high porosity is inserted into the channel. An experimental apparatus is a vertical rectangular flow channel with a square cross section in which one surface is heated by a rubber heater. Dimensions of the experimental apparatus is 600 mm in height and 50 mm on one side of the square cross section. Air was used as a working fluid and fine copper wire (diameter: 0.5 mm) was used as a porous material. The temperature of the wall surface and gas in the channel were measured by K type thermocouples. The flow velocity distribution was obtained by a PIV method. In this paper, we discuss the heat transfer and fluid flow characteristics of the proposed channel. From the results obtained in the experiment, it was found that the amount of removed heat decreased with increasing of temperature of gas when a copper wire was inserted into the channel with high porosity. This is because the mass flow rate decreased with increasing of viscosity of gas. Since it is expected that the porosity of a porous material will have an optimum value, further studies will be needed.

This paper presents an assessment of the performance of four eddy viscosity models in STAR-CCM+ 12.04 in simulating water flow through an industrial size butterfly valve: the standard k-ε model, realizable model, lag EB k-ε model and k-ω-SST model. This is achieved by comparing RANS predictions with physical measurements already available in literature. Although the lag EB k-ε model and k-ω-SST model are supposed to have a better ability to capture the anisotropic turbulence effect and flow separations, it has been demonstrated that the standard k-ε model is still a robust model in terms of predicting the flow coefficient (C v ). The general error of C v by the standard k-ε model is less than 10% for the considered openings with the exception of 80°. This work also demonstrates that the eddy viscosity models have more difficulty predicting the torque coefficient (C t ) than C v .

Multiphase flow widely exists in the nature and engineering. The two-phase flow is the highlight of the studies about the flow in the vessel and steam explosion in nuclear severe accidents. The Moving Particle Semi-implicit (MPS) method is a fully-Lagrangian particle method without grid mesh which focuses on tracking the single particle and concerns with its movement. It has advantages in tracking complex multiphase flows compared with gird methods, and thus shows great potential in predicting multiphase flows. The objective of this thesis is to develop a general multiphase particle method based on the original MPS method and thus this work is of great significance for improving the numerical method for simulating the instability in reactor severe accident and two-phase flows in vessel. This research is intended to provide a study of the instability based on the MPS method. Latest achievements of mesh-free particle methods in instability are researched and a new multiphase MPS method, which is based on the original one, for simulating instability has been developed and validated. Based on referring to other researchers’ papers, the Pressure Poisson Equation (PPE), the viscosity term, the free surface particle determination part and the surface tension model are optimized or added. The numerical simulation on stratification behavior of two immiscible flows is carried out and results are analyzed after data processing. It is proved that the improved MPS method is more accurate than the original method in analysis of multiphase flows. In this paper, the main purposes are simulating and discussing Rayleigh-Taylor (R-T) instability and Kelvin-Helmholtz (K-H) instability. R-T and K-H instability play an important role in the mixing process of many layered flows. R-T instability occurs when a lower density fluid is supported by another density higher fluid or higher density fluid is accelerated by lower density fluid, and the resulting small perturbation increases and eventually forms turbulence. K-H instability is a small disturbance for two different densities, such as waves, at the interface of the two-phase fluid after giving a fixed acceleration in the fluid. Turbulence generated by R-T instability and K-H instability has an important effect in applications such as astrophysics, geophysics, and nuclear science.

An ongoing Sandia National Laboratories’ (SNL) research study is evaluating a potential design of an injectable sacrificial material (SM) system that could contain and cool corium ejected from a reactor vessel lower head failure during a potential severe accident involving melting fuel at a commercial light water nuclear reactor (LWR). An injectable system could be installed at any existing LWR, without significant modification to the cavity or to the drywell pedestal region of the plant. The conceptual design under consideration is a passive system. The SM is being optimized to quickly cool the corium mixture while creating gas to form porosity in the solid, such that subsequent water flooding can penetrate the structure and provide additional cooling. The SM would form a barrier and limit corium-concrete interactions. This three-year project takes a joint experimental and computational approach. In this paper, we will first discuss the success of our small-scale experiments conducted on the interactions between the surrogate corium material (SCM) and SM, used to evaluate the injectable concept. A larger experimental study, currently underway, will further validate the injectable concept, with a focus on accurately measuring interactions. This paper details the modeling study and its progress, including modeling the experiments on a surrogate system and extending the model to bench-scale corium flow from validation experiments. The project’s modeling studies will use the SNL engineering code suite SIERRA Mechanics to understand the interaction of injectable SM and molten corium and predict corium spreading. Spreading is modeled using a level set method to track the front in conjunction with a pressure-stabilized finite element method on the fully three-dimensional mass, momentum, and energy conservation equations. Using this diffuse-interface method, the corium spreading front can be tracked and an appropriate pseudo-solidification viscosity models can be implemented to accurately model the corium spreading physics. Finally, an injectable SM delivery system is discussed along with its deployment to the six-common commercial LWR designs currently operating in the United States. At the end of this project, a simplified model based on SIERRA simulations will be developed for implementation into MELCOR, a severe reactor analysis code, developed at SNL for the U.S. Nuclear Regulatory Commission. This will allow us to demonstrate the ability of the injectable SM system to mitigate the ex-vessel corium spreading, provide containment and negate the release of radionuclides.

The reactor scram function realized by the rapidly dropping of control rods ensures safety when the reactor accidents (loss of electricity and earthquake, etc.) happen. In the thorium base molten salt reactor (TMSR - SF1), the rod drop time is obviously affected by the resistance which produced in the molten salt as its high density and viscosity. In this paper, the drop time of the control rod is obtained by the theoretical and experimental methods for comparison. Firstly, the drop time is analyzed both in air and water condition with calculation and experiment. And the method used for the resistance calculation of the rod during dropping is verified. Secondly, the similarity criterion is adopted to calculate the drop time in molten salt condition. The study shows that: 1) In air and water condition, the calculation is coincidence with the experimental results within the maximum error less than 2 %. 2) The drop time of the rod in molten salt is 2.8 s with a dropping height 2.4m in reactor, which satisfy the safety requirement of the control system. 3) It is necessary to use another buffer beside the disc spring to protect the driving mechanism of the rod during the rod dropping.

Oil coolers are widely-used in nuclear power plants which cool oil flowed through the bearing of steam turbines to a suitable temperature in order for the safe operation of steam turbines. Owing to the high viscosity, the flow state of oil is generally laminar flow or transition flow, which easily leads to poor heat transfer capability and thus a large volume of the oil coolers. The insertion of twisted tapes in circular tube is a passive method widely-used for enhancing heat transfer of laminar or transition flow. However, little research focuses on the heat transfer of highly-viscous fluids inside tube using the twisted tapes. The article will present the numerical simulations of the swirling flow induced by a new coaxial cross twisted tape inserts in a heat transfer tube with lubricating oil. The effects of the clearance ratios and twist ratios on oil side heat transfer coefficient, friction factor and performance evaluation criterion will be numerically investigated using CFD computer software STAR-CCM+. The clearance ratios are 0.077, 0.154 and 0.231. The twist ratios are 2.0 and 4.0. The boundary condition of simulation is constant wall temperature for the Reynolds number ranging from 200 to 1300. The results indicate that the new coaxial cross twisted tapes are efficacious in enhancing the heat transfer of the lubricating oil inside tube. When the clear ratio is 0.077, the effect of heat transfer enhancement of the coaxial cross twisted tapes is better than that of traditional twisted tapes. Furthermore, the highest performance evaluation criterion is up to 2.3.

690 nickel-based welding materials are widely applied on nuclear equipment manufacturing. While the nickel-based welding metal bath has the properties of high viscosity and poor fluidity, resulting in high susceptibility to welding cracking of the nickel-based weld metal, especially ductility dip cracking. As the nuclear key equipments serve in a severe condition combined with high pressure & temperature and corrosive atmosphere, the existence of micro crack would greatly affect the life expansion of the equipments. In this paper, WHS690M -alloy welding wire was developed in order to meet the requirement of CAP1400 nuclear power plant, which has good welding performance. Strain-to-fracture (STF) test based on Gleeble-3500 thermo-mechanical simulator was performed to evaluate the DDC susceptibility of Inconel 52M and WHS690M weld by different welding parameters. And combined with EBSD, the characteristics of grain orientation was also analyzed. The minimum critical strain in STF test appeared at 1050°C, and the value reached 3.2% for WHS690M while 2.1% for Inconel 52M. Furthermore, the critical strain for both WHS690M and Inconel 52M groove weld metal was about 2.0%, which was lower than cladding metal.

The motion of CRDM (Control Rod Drive Mechanism) is affected by the electro-magnetic force and the fluid resistance, also the movement process affected the control system. In this paper, we considered all the coupled factor and try to decouple the problem to several simple problems. We supposed 3 decoupling methods, and try to verification each assumption, and finally we found that an assumption is valid — the electromagnetic force is mainly affected by the displacement of CRDM in the attract process of kinetic jaw armature and kinetic jaw magnetic pole. We studied the fluid resistance force by CFD simulation, and exported the force to the electromagnetic model which is built by Infolytica/Magnet, the control system model is built by Matlab/Simulink coupling interface. In order to simulate the continuous movement process of CRDM, we studied the boundary data at each time period, and linked each period by in-house code. Then we tested the coupling simulation, listed the duration time of electric current and the movement duration time of mechanism. Compare to the test data, the maximum error is 17%. On the whole, this solution coupled CFD, electro-magnetic and control system, the simulation result can help engineers to optimize the control algorithm and shape design in a certain extent.

The objective of this paper is to act as a collection of multiple different heat-transfer correlations and to check their accuracy when compared to experimental data obtained in supercritical-pressure refrigerants (R-22 and R-134a). This paper is also intended to collect as much relevant data of heat transfer in supercritical refrigerants as possible for future research. The experimental data have been retrieved from graphs within a wide range of operating parameters. This study is in support of potential use of supercritical refrigerants as modeling fluids instead of supercritical water. The use of refrigerants as modelling fluids instead of water will allow to decrease costs and technical difficulties during experiments at supercritical pressures and widen operating ranges, because the critical parameters of refrigerants are significantly lower than those of water. The research was completed by collecting graphed data from several different experimental series using both R-22 and R-134a data. The advantage of comparing different refrigerants for determining correlation accuracy is to increase the predictability for other potential experiments using refrigerants. All data are taken from bare-tube experiments to produce a relative baseline for heat-transfer characteristics. These experiments have been performed within the following range: Inner tube diameter ranging between 4.4 mm to 13 mm, pressure ranging between 4.3 MPa to 5.5 MPa, and at a number of various mass and heat fluxes. Sixteen potential heat-transfer correlations have been selected and used in this assessment. The correlation by Watts and Chou [1] and Cheng et al. [2] were shown to have the lowest root-mean-square error. Other correlations with the reasonable accuracy include Mokry et al. [3] and Swenson et al. [4] correlations. However, it was decided to develop a new correlation based on these refrigerant data in an attempt to increase the prediction accuracy. Therefore, based on the Mokry et al. [3] correlation a modified correlation was developed, which generalized the experimental Freon data with higher accuracy than the know correlations. This correlation is intended to create a basis for further study on the use of refrigerants as modeling fluids. While Freon has similar properties to water at supercritical conditions, the different molecular properties causes factors to affect each fluid differently. For refrigerants at supercritical conditions, the factors that seem to have the most effect are the dynamic viscosity and density of a fluid.

Natural convection has been an area of intense research since it was discovered over 100 years ago. However, a phenomenological explanation for the onset of natural convection is still not available. The role of surface roughness in various thermal hydraulic phenomena is widely accepted; however, the scale of roughness is missing from Rayleigh number (Ra) which is commonly used to predict the onset of natural convection. Using the mass-spring analogy, an analytical derivation is presented to accurately characterize the thermal system and the interplay of gravity, viscosity and scale of roughness responsible for the onset of natural convection. The necessary conditions for the onset of natural convection are given in terms of a new dimensionless number β g Δ T ε H 2 α 2 which captures the effect of surface roughness. Using the mass-springs analogy, the natural frequency of the convection system is shown to depend on thermal and kinematic property of the fluid and the scale of roughness. These results are applicable to many natural system and engineering designs.

Hydrogen is adopted as coolant for regenerative cooling nozzle and reactor reflector in nuclear thermal propulsion (NTP), which may be a promising technology for human space exploration in the near future due to its large thrust and high specific impulse. During the cooling processes, the hydrogen experiences the transition from subcritical state to supercritical state, which influences the heat transfer severely. This paper is intended to study the characteristic of convective heat transfer to supercritical hydrogen in a straight tube under high heat flux through numerical simulation, which is a common phenomenon in NTP operation. The thermophysical properties and transport properties including the equation of state, specific heat capacity, viscosity and thermal conductivity of hydrogen are evaluated firstly by compared with the data from National Institute of Standards and Technology (NIST). Then, the flow and heat transfer process is investigated using Reynolds Averaged Naiver-Stokes (RANS) model, and the approach is validated by the successfully predicted behavior called local heat transfer deterioration. Moreover, the mechanism of heat transfer deterioration is analyzed briefly according to the detailed information of flow field. This work herein contributes to the further NTP design and research.

Firstly, using Fluent laminar model simulate volumetric flow rate and pressure differential. second, using Hagen Poiseuille formula calculate coefficient of dynamic viscosity. Then we can calculate laminar flow numerical simulation error of fluent by contrasting the difference of coefficient of dynamic viscosity between laminar simulative results of Fluent and calculated results of Hagen Poiseuille formula. Geometric model is Circular pipe. Fluid medium is water. The study found three conclusions. Fluent model relies on simplified mathematical formula, which can not accurately describe real flow situation, so Fluent simulation results is not accurate; When inlet velocity is at the range of 0.06m/s to 0.15m/s, Given coefficient of dynamic viscosity by Fluent model is always smaller than calculated coefficient of dynamic viscosity by Hagen Poiseuille formula; Laminar flow numerical simulation error of Fluent in circular tube gradually increase along with the increase of inlet velocity at the range of 0.06m/s to 0.15m/s.

Experimental study on resistance of air-water two-phase flow in a vertical 3 × 3 rod bundle was carried out under normal temperature and pressure. The rod diameter and pitch were 8 mm and 11 mm, respectively. The ranges of gas and liquid superficial velocity were 0.013∼3.763 m/s and 0.076∼1.792 m/s, respectively. The result indicated that the existing correlations for calculating frictional coefficient in the rod bundle and local resistance coefficient could not give favorable predictions on the single-phase experimental data. For the case of two-phase flow, eight correlations for calculating two-phase equivalent viscosity poorly predicted the frictional pressure drop, with the mean absolute errors around 60%. Meanwhile, the eight classical two-phase viscosity formulae were evaluated against the local pressure drop at spacer grid. It is shown that Dukler model predicted the experimental data well in the range of Re l <9000 while McAdams correlation was the best for Re l ⩾9000. For all the experimental data, Dukler model provided the best prediction with MRE of 29.03%. Furthermore, approaches to calculate two-phase frictional pressure drop and local resistance were proposed by considering mass quality, two-phase Reynolds number and densities in homogenous flow model, resulting in a good agreement with the experimental data.

During the severe accident, the core melt could leak out of the reactor pressure vessel through the broken instrument tubes of the RPV lower head. Thus, the melt freezing behavior in an instrument tube is a key factor that concerns the failure of the reactor pressure boundary. In this study, the Moving Particle Semi-implicit (MPS) method was adopted to analyze the melt penetration and solidification behaviors in a tube. The change of melt viscosity with temperature was taken into account in the present MPS method. The influence of surface tension on the melt penetration behavior was also considered. The numerical results had been compared with the upward melt injection experiments. The comparative results showed that the melt penetration lengths were in good agreement with the experiments. The typical melt freezing behaviors were successfully reproduced by MPS method. The crust formed on the surface of the tube increased the melt flowing resistance. The melt velocity also decreased due to the increase of its viscosity. The present results indicate that MPS method has the capacity to analyze the melt freezing behavior in the lower head penetration tubes.

In order to conform to the new regulatory standard in Japan, seawater is regarded as the alternative water source both for BWRs (Boiling water reactors) and PWRs (Pressurized water reactors). For preventing further accident evolutions occurred in Fukushima Daiichi nuclear power plants, seawater was injected into the reactors for more than one week. With long-term seawater injection, sea salt compositions are condensed and many of them will precipitate when saturated concentrations are exceeded. Unlike corrosion issues, impacts of sea salt precipitation on the heat removal has not been studied widely in the past because it has not been regarded as the alternative water source before Fukushima Daiichi nuclear power plants accident. The existent knowledge base of boric acid precipitation under LOCA conditions was studied. Based on the existent study on impacts of boric acid precipitation under LOCA conditions, the experimental project of seawater consisting of four experiments was proposed. The existent database of physical properties, such as viscosity, of seawater is rather poor under severe accident conditions. In addition, it is likely that boric acid will be injected with water or seawater to prevent re-criticality. It is known that physical properties of boric acid vary widely under high temperature conditions. Measurement of viscosity of the seawater-boric acid mixture was conducted in high temperature using a rotational viscometer. Under conditions equivalent to the estimated bulk coolant conditions under a long-term cooling phase of severe accidents. In this range, no obvious change of viscosity is expected. Then a detailed structure of seawater precipitates was observed using a mockup fuel bundle with 5×5 in the square lattice and 500 mm in the length. Images of precipitates were taken using the X-ray CT. The water level, the concentration of sea salt and the heat flux are employed as experimental parameters. The heat flux, bubble stirring in downstream of spacers and heat loss by a non-heated channel box were identified as influential factors to local and overall precipitates in fuel bundles.

This paper describes the results of ultrasonic examination of molten glass in the glass melter for the vitrification process of high-level radioactive liquid waste (HLW). The propagation and the attenuation of ultrasound in the molten glass were measured to study feasibility of detecting noble metal precipitates and the viscosity measurement of glass melter. The ultrasonic propagation experiment at 2.25MHz were carried out in a simulant fluid (glycerin) at room temperature and the molten glass at 1000°C using ultrasonic wave guide rods. The wave guide rod materials used in this research are a nickel-based heat resistant alloy 690 and a high density isotropic graphite T-6 (Ibiden Co., Ltd.) with a corrosion resistant coating. Although the nickel-based alloy 690 has a favorable property such as superior structural integrity or corrosion resistant against molten glass at high temperatures, the ultrasonic attenuation was quite large thereby not suited for the wave guide rod. On the other hand, the wave guide rod made of high density isotropic graphite showed good capabilities of ultrasonic propagation both in glycerin and the molten glass at 1000°C. The changes in ultrasonic intensity of reflecting echoes vs. distance were measured both in glycerin and the molten glass to obtain attenuation coefficient of ultrasound. Then, the viscosity of glycerin and molten glass was calculated from the result of ultrasonic attenuation measurement. The viscosity of glycerin and molten glass thus obtained showed good agreement with those obtained by ordinary viscous test.

A computational study of a thermal striping in the upper plenum of the PGSFR (Prototype Generation-IV Sodium-cooled Fast Reactor) being developed at KAERI (Korea Atomic Energy Research Institute) is presented. First, previous experimental and numerical studies on the thermal striping are briefly discussed. Both RANS (Reynolds-Averaged Navier-Stokes) and LES (Large Eddy Simulation) approaches are employed for the simulation of thermal striping in the upper plenum of the PGSFR. For the RANS approach, the conventional k – ε turbulence model is employed and the LES is performed using the WALE (Wall-Adapting Local Eddy-viscosity) model. More than 11.8 million unstructured elements are generated in the upper plenum region of the PGSFR using the ICEM commercial code. From the RANS results, the time-averaged velocity components and temperature field in the complicated upper plenum of PGSFR are calculated. In the LES results, the time history of temperature fluctuation at the several locations of solid walls of UIS (Upper Internal Structure) and IHX (Intermediate Heat Exchanger) are additionally stored. Comparisons of the predicted time-averaged velocity components and temperature between the two methods are also presented. From the temporal variation of temperature at the solid walls, one can find the locations where the thermal stress is large and assess whether the solid structures can endure the thermal stress during the reactor life time.