Experimental Investigations of the Thermohydraulic Parameters of the Flow Section of a Liquid-Metal Target with a Window for a Proton Beam from an Accelerator

The results of computational and experimental investigations of the thermohydraulic characteristics of a liquid-metal target with a tight-fitting stopper, whose shape ensures a constant energy-release volume in the stopper material, are examined. The investigations on water circulation stands included flow visualization and measurement of the velocity and pressure distributions in the flow part of the target structure. The investigations on the liquid-metal circulation stand with lead-bismuth coolant were performed with coolant working temperature 300°C and maximum flow rate up to 7 m³/h. The temperature and the temperature pulsations in the coolant and in the material of the tight-fitting stopper were determined.     

Thermal Experiments on a Model of a Target for an Accelerator-Driven System

The results of experiments performed on a model of a window target of an accelerator-driven system are presented. The model, the special features of the structure, and the measurement systems and methodological approaches are briefly described. A eutectic sodium–potassium alloy is used to simulate the lead–bismuth eutectic alloy. The following characteristics were measured directly in the experiments or obtained by analyzing the experimental data: coolant flow rate, power, absolute coolant temperature as a function of distance from the target membrane, the absolute temperature of the membrane surface as a function of the distance from the membrane center, the standard deviations of the indicated quantities and the pulsations of the coolant and membrane temperatures. The measurements showed that large temperature pulsations are observed on the membrane surface; these must be taken into account when analyzing the strength characteristics of a real target setup.     

Experimental study on the Reynolds number dependence of turbulent mixing in a rod bundle

An experimental study for Reynolds number dependence of the turbulent mixing between fuel-bundle subchannels, was performed. The measurements were done on a triangular array bundle with a 1.20 pitch to diameter relation and 10 mm rod diameter, in a low-pressure water loop, at Reynolds numbers between 1.4 × 10³ and 1.3 × 10⁵.The high accuracy of the results was obtained by improving a thermal tracing technique recently developed. The Reynolds exponent on the mixing rate correlation was obtained with two-digit accuracy for Reynolds numbers greater than 3 × 10³. It was also found a marked increase in the mixing rate for lower Reynolds numbers.The weak theoretical base of the accepted Reynolds dependence was pointed out in light of the later findings, as well as its ambiguous supporting experimental data.The present results also provide indirect information about dominant large scale flow pulsations at different flow regimes.     

Determination of the distribution of air and water in porous media by electrical impedance tomography and magneto-electrical imaging

Monitoring the distribution of water content is essential for understanding hydrological processes in the lithosphere and the pedosphere. The movement of water in unsaturated rock formations and in the vadose zone is influenced by different processes (mainly infiltration, evaporation, percolation and capillary flow) which may be rate determining depending on the actual conditions. The interdependence of these processes also strongly influences the transport and distribution of solutes in the pore space. In order to gain a better understanding of the movement and distribution of water in unsaturated media, systematic investigations with non-invasive or minimal invasive methods appear to be most suitable. Studies on the distribution of electrical conductivity can improve risk analysis concerning waste disposals in general and nuclear waste repositories in particular. Induced polarization and magnetic flux density determined with two highly sensitive accessories yield additional information and may allow for better discrimination of coupled flow processes. Electrical impedance tomography (EIT) with 20 current injection and 48 voltage electrodes was used here to monitor the evaporation of tap water from a container filled with sand under laboratory conditions at 20 °C. The results are compared with data obtained by determining spectral induced polarization (SIP) of sand during desaturation in a multi-step outflow equipment. Infiltration processes and evaporation from sand saturated with 0.01 M CaCl₂ were determined by magneto-electrical resistivity imaging technique (MERIT). The results were obtained from a long-term experiment under controlled conditions.     

Simulation of flow pulsations in a twin rectangular sub-channel geometry using unsteady Reynolds Averaged Navier-Stokes modelling

An unsteady Reynolds Averaged Navier-Stokes (URANS) based turbulence model, the Spalart-Allmaras (SA) model, was used to investigate the flow pulsation phenomena in compound rectangular channels for isothermal flows. The studied geometry was composed of two rectangular sub-channels connected by a gap, on which experiments were conducted by Meyer and Rehme (1994) and were used for the validation of numerical results. Two case studies were selected to study the effect of the advection scheme. The results from the first order upwind advection scheme had clear symmetry and periodicity. The frequency of flow pulsations was under predicted by almost a factor of two. Due to inevitable numerical diffusion of the first order upwind scheme, a second order accurate in space advection scheme was also considered. The span-wise velocity contours, velocity vector plots, and time traces of the velocity components showed the expected cross-flow mixing between the sub-channels through the gap. The predicted kinetic energy in the unsteady velocity fluctuations showed two clear peaks at the edges of the gap. The dynamics of the flow pulsations were quantitatively described through temporal auto-correlations and power spectral functions. The numerical predictions were in agreement with the experiments. Studies on the effect of the Reynolds number and the computational length of the domain were also performed. The numerical results reproduced the relationship between the Reynolds number and the frequency of the flow pulsations. The impact of the channel length was tested by simulating a longer channel with respect to the base case. It was found that the channel length did not significantly affect the numerical predictions. Simulations were also performed using the standard k-? model. While the flow pulsations were predicted with this model, the frequency of the pulsation was in poor agreement with the experimentally measured value.     

Prediction of temperature and water level in a spent fuel pit during loss of all AC power supplies

A prediction method for water temperature in a spent fuel pit of a pressurized water reactor (PWR) has been developed to calculate the increase in water temperature during the shutdown of cooling systems. In this study, the prediction method was extended to calculate the water level in a spent fuel pit during loss of all AC power supplies, and predicted results were compared with measured values of spent fuel pools in the Fukushima Daiichi Nuclear Power Station. The calculations gave reasonable results, but overestimated the decreasing rate of the water level and the water temperature. This indicated that decay heat was overestimated and evaporation heat transfer from the water surface was underestimated. Results of calculations with 80% decay heat and 155% (Unit 4 pool) or 230% (Unit 2 pool) evaporation heat flux were in good agreement with measured values. The data-fitted evaporation heat fluxes agreed rather well with the evaporation heat transfer correlation proposed by Fujii et al.     

Manufacturing and testing of a HETS module for DEMO divertor

The development of a divertor concept for fusion power plants that is able to grant efficient recovery and conversion of the considerable fraction (～15%) of the total fusion thermal power incident is deemed to be an urgent task to meet in the EU Fast Track scenario. The He-cooled conceptual divertor design is one of the possible candidates. Helium cooling offers several advantages including chemical and neutronic inertness and the ability to operate at higher temperatures and lower pressures than those required for water cooling. The HETS (high-efficiency thermal shield) concept, initially developed by ENEA for water, has been adapted for use with He as coolant. This DEMO divertor concept is based on elements joined in series and protected by a hemispheric dome; it allows an increase of thermal exchange coefficient both for high speed of gas and for “jet impingement” effects of gas coming out from the internal side of hemispheric dome. It has been calculated to be capable of sustaining an incident heat flux of 10 MW/m² when operating at 10 MPa, an inlet He temperature of 600 °C, and an outlet temperature of 800 °C. The presented activity, performed in the frame of EFDA-TW5TRP-001 task, was focused on the manufacturing of a single HETS module and on its thermal–hydraulic testing. The materials used for the HETS module manufacturing were all DEMO-compatible: W for the armor material and the hemispherical-dome, DENSIMET for the exchanger body. The testing is performed by connecting the module to HEFUS3 He loop system that is a facility able to supply the He flow to the required testing conditions: 400 °C, 4–8 MPa and 20–40 g/s. The needed incident heat flux is obtained by RF inducting equipment coupled to an inductor coil installed just over the HETS module. A CFD analysis by ANSYS-CFX was performed in order to predict the thermal–mechanical behavior of the module and a final comparison with the experimental data is required to validate the CFD results. All parameters are monitored and recorded by data acquisition system.     

中性束注入器水流热量计系统优化分析

介绍了用于计算中性束注入实验中束流功率沉积的水流热量计系统优化及优化后的测试结果。前期的水流热量计系统利用串口传输和分散式牛顿模块采集,采样率低、传输速度慢、抗干扰能力差、无法满足实验要求;优化后的系统基于虚拟仪器,采用TCP\IP协议传输和虚拟仪器技术,提高了系统的采样率和精度、优化了数据传输速度及抗干扰能力。优化后的系统经测试可以准确监测中性束注入器装置上各热承载部件冷却水的温升及流量,并分析得到中性束注入时束流在各热承载部件上的功率沉积。实验结果表明优化后的系统工作稳定,使用灵活,数据准确,满足实验要求。     

Pulsational characteristics of two-cassette model of boiling-water reactor

Conclusions On a large-scale two-cassette model of the natural-circulation loop of a reactor with vertical dimensions and reduced hydraulic-drag coefficients of the basic loop elements that are close to the full-scale values, an experimental investigation has been conducted, with the following conclusions:With design parameters of the heat carrier, the specific thermal stress of the fuel elements, and the discrepancy coefficients of the pile power, the zone of hydrodynamic instability is characterized by the values ; liquidation of total-loop pulsations of the heat-carrier flow rate entails vapor condensation under the water level in the reactor; total liquidation of the pulsations requires, in addition, the introduction of disks at the input to each pile; the reduced hydraulic-drag coefficient _re of the disk must be no less than 0.8 of the sum of _re for the pile and the ITS.Translated from Atomnaya Énergiya, Vol. 69, No. 2, pp. 87–92, August, 1990.     

New thermal optimization scheme of power module in solid-state amplifier

The new 1 kW power module for ADS project needs the optimization of cooling design including water flow and tunnel layout, and the water flow of three tons per hour was chosen to be a goal for a 20 kW power source.According to analysis from the insertion and integrated loss, about 24 modules were integrated into the rated power. Thus, every module has a cooling flow of 2.1 L/min for RF heat load and power supply loss, which is very hard to achieve if no special consideration and techniques. A new thermal simulation method was introduced for thermal analysis of cooling plate through CST multi-physics suite,especially for temperature of power LDMOS transistor.Some specific measures carried out for the higher heat transfer were also presented in this paper.     

Thermal-hydraulic design of water-cooled pressure tube blanket for a fusion driven subcritical reactor

A Water-cooled Pressure Tube Energy production blanket (WPTE) for fusion driven subcritical reactor has been designed to achieve 3000 MW thermal power with self-sustaining tritium cycle. Pressurized water has great advantages in energy production; however the high pressure may cause some severe structural design issues. This paper proposes a new concept of water-cooled blanket. To solve the problem of the high pressure of the coolant, the pressure tube was adopted in the design and in the meantime, the thickness of the first wall can be significantly reduced as result of adopting pressure tube. The numerically simulating and calculating of temperature, stress distribution and flow analyses were carried out and the feasibility of using water as coolant was discussed. The results demonstrated the engineering feasibility of the water-cooled fusion–fission hybrid reactor blanket module.     

Measurement of the Characteristics of the Ventilation Pipe of the Filtration System for the Steam-Gas Medium of a Nuclear Power Plant

The dependence of the heat power of a pipe (air–air heat exchanger) on the flow rate and the temperature of the heating air is investigated experimentally. The temperature fields along the height of the pipe are measured. In the experimental velocity range 1.2–9.5 m/sec and heating-air temperature range 120–280°C, the heat power depends strongly on the temperature and negligibly on the flow rate of the heating air. Increasing the cold-air flow rate increases the thermal power in direct proportion.     

Transient behaviors of heavy water reflector system during postulated initiating events (PIEs)

This study investigates the transient thermal-hydraulic behaviors of a heavy water reflector system during various postulated initiating events (PIEs). The following events are considered in the analysis: (1) loss of heavy water system (HWS) flow, (2) heavy water leakage, (3) loss of secondary cooling flow, and (4) dilution of heavy water. The sequence of each event is described, and thermal-hydraulic parameters such as the heavy water temperature, system pressure, flow rate, and heavy water level are monitored. To regulate the HWS, the heavy water temperature at the outlet of the heavy water vessel, the heavy water level in the expansion tank, and the flow rate in the HWS are used as the reactor regulating system (RRS) setbacks. In the event of loss of HWS flow, the standby pump kicks off to recover it, and none of the RRS setback signals are triggered. In the event of heavy water leakage, a low-level RRS setback signal trips the reactor, and the temperature rise in the HWS is not significant. The total amount of heavy water leakage with a break at the outlet of the heat exchanger is approximately 550 L. In the event of loss of secondary cooling flow, a high-temperature RRS setback signal trips the reactor. In the event of heavy water dilution, a low-level RRS setback signal trips the reactor. In the case of a pipe rupture at the highest point in the HWS inside the pool, the RRS setback signal is triggered at 83.9 s from the initiation. At the instant of the reactor trip, the reactor power increases to 150% of full power because of the degraded purity of the heavy water––95.7%. For the event of heavy water dilution, a reactor protection system (RPS) setback such as the reactor power difference between a neutron detector and a gamma detector should be used to trip the reactor.     

Natural circulation experiments in a non-uniform diameter lead bismuth loop and validation of LeBENC code

Experimental studies are carried out on natural circulation in a Lead Bismuth Eutectic (LBE) loop. The loop mainly consists of a heated section, air heat exchanger, valves, various tanks and argon gas control system. All the components and piping are made of SS316L. The dissolved oxygen in the LBE is monitored online by an Yttria Stabilised Zirconia (YSZ) oxygen sensor and controlled during the operation of the loop. In this paper the details of the loop and experimental studies carried out with heater power levels varying from 900 W to 5000 W are described. The temperature range of LBE during the experiments was 200 °C–500 °C. The maximum heat loss in the piping is kept less than 20% of the main heater power. Steady state experimental studies are carried out at different power levels and the LBE flow rate was found to be varying from 0.095 kg/s to 0.135 kg/s. The analysis and results of the performance of the heat exchanger with air and water as the secondary coolants are also discussed in the paper. Transient studies were carried out to simulate various events like heat sink loss, step power change and secondary side coolant flow rate change and reported in the paper. In the start up experiments, where the flow is started from stagnant condition of LBE, the time required for starting of natural circulation is found to be 600 s, 400 s and 240 s with power level of 1200 W, 2400 W and 3000 W respectively. The results are compared with available correlation and prediction of computer code LeBENC.     

Outgassing measurement of the waveguide module for a steady state LHCD antenna

An outgassing rate is measured using a waveguide module during a long pulse r.f. injection at 3.7 GHz in order to operate a lower hybrid current drive (LHCD) antenna in steady state. The waveguide module consists of four sub-waveguides which are made of dispersion-strengthened copper and copper-plated stainless steel with cooling channels to control its working temperature between 100 and 500 °C. The waveguide module shows the high power capability of power density up to 200 MW m⁻² after short term conditioning. A low outgassing rate of about 2 × 10⁻⁷ Pa m³ s⁻² m⁻² is obtained during r.f. injection up to 150 MW m⁻² at a working temperature of T=300 °C after 450 °C baking. Long pulse r.f. injection is effective for reduction of the outgassing by about 1/100. Outgassing during r.f. injection depends on the working temperature but is independent of the r.f. power density after sufficient conditioning. The calculation code taking desorption, adsorption and diffusion processes into account can show time behavior of outgassing in the waveguide module. A quasi-constant outgassing of about 10⁻⁷ Pa m³ s⁻¹ m⁻² is observed at a power density of 150 MW m⁻² in 1800 s injection while keeping a saturated temperature at the center of the module below 120 °C by using water cooling. The outgassing properties obtained indicate that steady state operation of an LHCD antenna is feasible without a large pumping system.     

Experimental study on the air/water counter-current flow limitation in a model of the hot leg of a pressurized water reactor

An experimental investigation on the air/water counter-current two-phase flow in a horizontal rectangular channel connected to an inclined riser has been conducted. This test-section representing a model of the hot leg of a pressurized water reactor is mounted between two separators in a pressurized experimental vessel. The cross-section and length of the horizontal part of the test-section are (0.25 m × 0.05 m) and 2.59 m, respectively, whereas the inclination angle of the riser is 50°. The flow was captured by a high-speed camera in the bended region of the hot leg, delivering a detailed view of the stratified interface as well as of dispersed structures like bubbles and droplets. Countercurrent flow limitation (CCFL), or the onset of flooding, was found by analyzing the water levels measured in the separators. The counter-current flow limitation is defined as the maximum air mass flow rate at which the discharged water mass flow rate is equal to the inlet water mass flow rate.From the high-speed observations it was found that the initiation of flooding coincides with the formation of slug flow. Furthermore, a hysteresis was noticed between flooding and deflooding. The CCFL data was compared with similar experiments and empirical correlations available in the literature. Therefore, the Wallis-parameter was calculated for the rectangular cross-sections by using the channel height as length, instead of the diameter. The agreement of the CCFL curve is good, but the zero liquid penetration was found at lower values of the Wallis parameter than in most of the previous work. This deviation can be attributed to the special rectangular geometry of the hot leg model of FZD, since the other investigations were done for pipes.     

Thermal-hydraulic characteristics of a single-phase natural circulation loop with water and Al2O3 nanofluids

A natural circulation system operates on the basis of natural laws like gravity and buoyancy. Although natural circulation is a benign gift of nature for applications to several heat removal systems due to their simplicity in design, elimination of hazards related to pumps, better flow distribution, cost reduction, etc. however, the potential threat of flow instabilities still eludes for its wide applications. Although addition of local losses (orificing) may suppress instabilities, however, it is accompanied by significant flow reduction which is detrimental to the natural circulation heat removal capability. In this paper, we have demonstrated experimentally, with nanofluids, not only the flow instabilities are suppressed but also the natural circulation flow rate is enhanced. The increase in steady natural circulation flow rate due to addition of nanoparticles is found to be a function of its concentration in water. The flow instabilities are found to occur with water alone only during a sudden power addition from cold condition, step increase in power and step decrease in power (step back conditions). With a small concentration of Al₂O₃ nanofluids, these instabilities are found to be suppressed significantly.     

Thermal and stability considerations for a supercritical water-cooled fast reactor with downward-flow channels during power-raising phase of plant startup

This paper describes study on the procedure of raising the reactor thermal power and the reactor coolant flow rate during the power-raising phase of plant startup for the supercritical water-cooled fast reactor (SWFR), which is selected as one of the Generation IV reactor concepts. Since part of the seed fuel assemblies and all the blanket fuel assemblies of the SWFR are cooled by downward flow, the feedwater from the reactor vessel inlet nozzle to the mixing plenum located below the core is distributed among these fuel assemblies and the downcomer. The flow rate distribution as the function of both the reactor thermal power and the feedwater flow rate, which are the design parameters for the power-raising phase, is obtained by the thermal hydraulic calculations. Based on the flow rate distribution, thermal analyses and thermal-hydraulic stability analyses are carried out in order to obtain the available region of the reactor thermal power and the feedwater flow rate for the power-raising phase. The criteria for the “available” region are the maximum cladding surface temperature (MCST) and the decay ratio of thermal-hydraulic stability in three “hot” channels; two seed assemblies with upward/downward flow and a blanket assembly. The effects of various heat transfer correlations and axial power distributions are also studied.     

Chemical Tracer Method for Measurement of Flow Rates in Closed Conduits

Thermal output in a nuclear power plant is verified by a calorimetric heat balance on the secondary system of the power plant. The calorimetry involves the precise measurement of the feed water flow rate which should be designed to have ±1:0% of uncertainty. However, the indication of feed water flow rate obtained by a differential pressure measurement across a venturi can be affected by instrument errors, fouling, or a poorly developed velocity profile. These factors can lead to an inaccurate mass flow rate and consequently, an inaccurate estimate of power. The purpose of this study is to develop verification methods with accuracy better than ±0:5% for high-precision flow measurement to be used for measuring feed water flow rate. Such an improvement saves electric power. For a typical Korean nuclear power plant of 1,000MW, 10MW would be potentially saved. This chemical tracer method is a testing process using a tracer, which can be applied to quantify losses in electrical output caused by incorrect measurement of feed water flow rate. This method has a good response to changes in the flow rate. An accuracy better than 0.5% is expected for feed water flow measurement, provided that the feed water system is stabilized during the test.     

Erratum to “Experimental study on the air/water counter-current flow limitation in a model of the hot leg of a pressurized water reactor”

This paper replaces the paper published in the journal by Deendarlianto et al. (2008). Because of an error in the implementation of the air flow meter some of the data given by Deendarlianto et al. (2008) are wrong. They are corrected within the present paper. The general results and conclusions remain unchanged.An experimental investigation on the air/water counter-current two-phase flow in a horizontal rectangular channel connected to an inclined riser has been conducted. This test-section representing a model of the hot leg of a pressurized water reactor is mounted between two separators in a pressurized experimental vessel. The cross-section and length of the horizontal part of the test-section are (0.25 m × 0.05 m) and 2.59 m, respectively, whereas the inclination angle of the riser is 50°. The flow was captured by a high speed camera in the bended region of the hot leg, delivering a detailed view of the stratified interface as well as of dispersed structures like bubbles and droplets. Counter-current flow limitation (CCFL), or the onset of flooding, was found by analyzing the water levels measured in the separators. The counter-current flow limitation is defined as the maximum air mass flow rate at which the discharged water mass flow rate is equal to the inlet water mass flow rate.From the high-speed observations it was found that the initiation of flooding coincides with the formation of slug flow. Furthermore, a slight hysteresis was noticed between flooding and deflooding. The CCFL data was compared with similar experiments and empirical correlations available in the literature. Therefore, the Wallis-parameter was calculated for the rectangular cross-sections by using the channel height as length, instead of the diameter. The agreement of the CCFL curve is good, but the zero liquid penetration was found at lower values of the Wallis parameter than in most of the previous work. This deviation can be attributed to the special rectangular geometry of the hot leg model of HZDR, since the other investigations were done for pipes.