Hideki Kamide

Experimental Study on Gas Entrainment at Free Surface in Reactor Vessel of a Compact Sodium-Cooled Fast Reactor

An innovative sodium-cooled fast reactor has been investigated as part of the fast reactor cycle technology development (FaCT) project. In the reactor, a compact reactor vessel (R/V) with increased sodium flow velocity was designedto reduce the construction cost. One of the thermal hydraulic problems associated with this design is gas entrainment at the free surface in the R/V. Horizontal plates are set below the free surface in order to prevent the gas entrainment. A water experiment was performed using a partial model built to 1/1.8 scale. The objective was to investigate the occurrence of gas entrainment under certain conditions and the mechanism of the gas entrainment. It was found that there were two types of gas entrainment phenomenon, and the conditions for their occurrence were far different from the rated condition in the reactor. One type of gas entrainment occurred at the wake region of flow around the cold leg pipe created due to the larger horizontal velocity in the R/V. The other type of gas entrainment occurred at the region between the hot leg pipe and the R/V wall when the coolant level was low and the downward velocity was large. The mechanisms of the gas entrainment at the two regions were clarified by the detailed measurement of transient flow velocity field.

Transient Behavior of Gas Entrainment Caused by Surface Vortex

A compact sodium-cooled reactor is an important candidate as a fast breeder reactor (FBR) and has been investigated in the feasibility study of FBR cycle. Due to the compact sizing of the reactor vessel, gas entrainment at the free surface of sodium coolant becomes one of the significant issues for reactor design, and it is required to clarify the criterion of gas entrainment at free surface and the tolerance. In the present study, some visualization experiments were performed in a water-air system focusing on the gas entrainment due to surface vortex and its transient phenomena. Influences of horizontal velocity were clarified by the visualization. The gas entrainment due to the surface vortex occurs intermittently. Time trends of circulation and length of gas core for the intermittent surface vortices were measured by the particle image velocimetry and visualization. It was found that the gas core length extends with time delay to the increase of circulation around the vortex.

Large Eddy Simulation of Highly Fluctuational Temperature and Velocity Fields Observed in a Mixing-Tee Experiment

Abstract The WATLON water experiment about fluid mixing in a tee pipe is calculated with a finite element volume method and a large eddy simulation (LES) approach, with the TRIO-U code. Its unstructured tetrahedron grids do not lead to the same noteworthy disagreements previously mentioned with Cartesian grids. Branch and main pipe inlet velocity fluctuations due to turbulence are simulated with the use of “periodic boxes.” These more realistic inlet fluctuations allow physical instabilities to develop, improving the predictions. When an elbow is added upstream of the injection, the influence of the secondary flow on temperature-averaged values and fluctuations is underlined.

A high-precision calculation method for interface normal and curvature on an unstructured grid

In the volume-of-fluid algorithm, the calculations of the interface normal and curvature are crucially important for accurately simulating interfacial flows. However, few methods have been proposed for the high-precision interface calculation on an unstructured grid. In this paper, the authors develop a height function method that works appropriately on an unstructured grid. In the process, the definition of the height function is discussed, and the high-precision calculation method of the interface normal is developed to meet the necessary condition for a second-order method. This new method has highly reduced computational cost compared with a conventional high-precision method because the interface normal calculation is completed by solving relatively simple algebraic equations. The curvature calculation method is also discussed and the approximated quadric curve of an interface is employed to calculate the curvature. Following a basic verification, the developed height function method is shown to successfully provide superior calculation accuracy and highly reduced computational cost compared with conventional calculation methods in terms of the interface normal and curvature. In addition, the height function method succeeds in calculating accurately the slotted-disk revolution problem and the oscillating drop on unstructured grids. Therefore, the developed height function method is confirmed to be an efficient technique for the high-precision numerical simulation of interfacial flows on an unstructured grid.

Effect of Experimental Conditions on Gas Core Length and Downward Velocity of Free Surface Vortex in Cylindrical Vessel

This paper deals with characteristics of surface vortex in a cylindrical vessel. One of the characteristics is a gas core length, which is important to estimate the onset condition of the gas entrainment but influenced easily by the experimental condition. In the experiment using water, the effects of the water temperature, water level, and the surface tension on the gas core length were investigated. The onset condition of the gas entrainment is sometimes estimated by using the Burgers vortex model but the real flow in the vessel is different from the model. The velocity fields were measured by particle image velocimetry (PIV) and the velocity gradient of the downward flow was discussed. The proper flow conditions for the Burgers vortex model are a high water level and a high flow rate.

Development of an evaluation methodology for the natural circulation decay heat removal system in a sodium cooled fast reactor

A natural circulation evaluation methodology has been developed to ensure the safety of a sodium-cooled fast reactor (SFR) of 1500 MW adopting the natural circulation decay heat removal system (NC-DHRS). The methodology consists of a one-dimensional safety analysis which can evaluate the core hot spot temperature taking into account the temperature flattening effect in the core, a three-dimensional fluid flow analysis which can evaluate the thermal-hydraulics for local convections and thermal stratifications in the primary system and DHRS, and a statistical safety evaluation method for the hot spot temperature in the core. The safety analysis method and the three-dimensional analysis method have been validated using results of a 1/10 scaled water test simulating the primary system of the SFR and a sodium test simulating a part of the primary system and the DHRS with about a 1/7 scale, and the applicability of the safety analysis for the SFR has been confirmed by comparing with the three-dimensional analysis adopting the turbulence model. Finally, a statistical safety evaluation has been performed for the SFR using the safety analysis method.

Study on Thermal Striping at UIS of Advanced Loop Type Fast Reactor: Water Experiment Using a 1/3 Scale 60 Degree Sector Model

An advanced loop type sodium cooled fast reactor, JSFR, has been investigated in the frame work of Fast Reactor Cycle Technology Development Project (FaCT). As the temperatures difference between the control rod channels and the core fuel subassemblies is around 100 °C, temperature fluctuation due to the fluid mixing at the core outlet may cause high cycle thermal fatigue at the bottom of Upper Internal Structure (UIS). Then, a water experiment was conducted using an 1/3 scale 60 degree sector model. Temperature and its fluctuation intensity distributions around the control rod were measured and an effect of the improved structure against the thermal fatigue was examined.© 2009 ASME

An experimental study on natural circulation decay heat removal system for a loop type fast reactor

ABSTRACT A fully natural circulation-based system is adopted in the decay heat removal system (DHRS) of an advanced loop type fast reactor. Decay heat removal by natural circulation is a significant passive safety measure against station blackout. As a representative of the advanced loop type fast reactor, DHRS of the sodium fast reactor of 1500 MWe being designed in Japan comprises a direct reactor auxiliary cooling system (DRACS), which has a dipped heat exchanger in the reactor vessel, and two units of primary reactor auxiliary cooling system (PRACS), which has a heat exchanger in the primary-side inlet plenum of an intermediate heat exchanger in each loop. The thermal-hydraulic phenomena in the plant under natural circulation conditions need to be understood for establishing a reliable natural circulation driven DHRS. In this study, sodium experiments were conducted using a plant dynamic test loop to understand the thermal-hydraulic phenomena considering natural circulation in the plant under a broad range of plant operation conditions. The sodium experiments simulating the scram transient confirmed that PRACS started up smoothly under natural circulation, and the simulated core was stably cooled after the scram. Moreover, they were conducted by varying the pressure loss coefficients of the loop as the experimental parameters. These experiments confirmed robustness of the PRACS, which the increasing of pressure loss coefficient did not affect the heat removal capacity very much due to the feedback effect of natural circulation.

Investigation on Slit Jet through Upper Internal Structure (UIS) in Highly Compact Vessel of Sodium-Cooled Fast Reactor

An advanced loop-type sodium-cooled fast reactor has been developed by the Japan Atomic Energy Agency. The upper internal structure (UIS) above the core is a key component where control rod guide tubes are housed. A radial slit is set in the UIS to simplify the fuel-handling system and to reduce the reactor vessel diameter. A high-velocity upward flow is formed in the UIS slit. This slit jet influences thermal hydraulic issues in the reactor vessel. A water experiment was carried out to understand the flow field in the UIS, which is composed of the control rod guide tubes and several horizontal perforated plates with a slit. A refractive index matching method was applied to visualize the flow in such a complex geometry. Velocity measurement using particle image velocimetry showed that the velocity in the UIS slit was accelerated by the multiple slits and kept at a high value at the mid-height of the reactor upper plenum. A numerical simulation was carried out for this complex geometry of the UIS to obtain an adequate simulation method. A comparison between the experimental and analytical velocity profiles showed that the numerical simulation is highly applicable.

Experimental Study on Gas Entrainment Due to Nonstationary Vortex in a Sodium Cooled Fast Reactor—Comparison of Onset Conditions Between Sodium and Water

An innovative sodium cooled fast reactor has been investigated as part of the fast reactor cycle technology development project. In the reactor, a compact reactor vessel (R/V) with increased sodium flow velocity was designed to reduce the construction cost. One of the thermal hydraulic problems in this design is gas entrainment at the free surface in the R/V. In most of past studies, water experiments were performed to investigate the gas entrainment in the reactor. It is necessary to evaluate an influence of fluid physical property on the gas entrainment phenomena. In this study, sodium experiments were carried out to clarify the onset criteria of the gas entrainment due to a free surface vortex. Water experiments using a test section in which geometry is the same as that in the sodium tests were also performed. The gas entrainment in water slightly tended to take place in comparison with that in sodium under low velocity conditions. Overall, the onset condition map on the lateral and downward flow velocities in the sodium and water experiments were in good agreement.