Li Jet Research Articles

Wave period of free-surface waves on high-speed liquid lithium jet for IFMIF target

Wave period of free-surface waves on a high-speed liquid lithium (Li) jet has been experimentally studied for validation of a Li target of the International Fusion Materials Irradiation Facility (IFMIF), since stability of the jet is of crucial importance for generating high neutron fluence and for the safety of IFMIF itself. The experiments were conducted at a Li loop in Osaka University. In this loop, a plane Li wall jet of 70 mm in width and 10 mm in depth simulating the IFMIF Li target can be tested at the velocities of up to 15 m/s at the operation temperature of 573 K. In measurement of the wave period, the contact type liquid level sensor was used. As a result, probability density distribution of the wave period was found to be very similar to the log-normal distribution. From our previous and the present results, it is concluded that random wave property developed for the ocean waves can apply to the free-surface waves on the Li jet, irrespective of difference in the materials properties of Li and water.

ICONE19-43608 DIAGNOSTICS OF HIGH-SPEED LIQUID LITHIUM JET FOR IFMIF/EVEDA LITHIUM TEST LOOP

Regarding R&Ds on the International Fusion Materials Irradiation Facility (IFMIF), hydraulic stability of the liquid Li jet simulating the IFMIF Li target is planned to be validated using EVEDA Li Test Loop (ELTL). IFMIF is an accelerator-based deuteron-lithium (Li) neutron source for research and development of fusion reactor materials. The stable Li target is required in IFMIF to maintain the quality of the neutron fluence and integrity of the Li target itself. This paper presents diagnostics of the Li jet to be implemented in validation tests of the jet stability in ELTL, and those specifications and methodologies are introduced. In the tests, the following physical parameters need to be measured; thickness of the jet; surface structure (height, length/width and frequency of free-surface waves); local flow velocity at the free surface; and Li evaporation rate. With regard to measurement of jet thickness and the surface wave height, a contact-type liquid level sensor is to be used. As for measurement of wave velocity and visual understanding of detailed free-surface structure, a high-speed video camera is to be leveraged. With respect to Li evaporation measurement, weight change of specimens installed near the free surface and frequency change of a crystal quartz are utilized.

Hydraulics and heat transfer in the IFMIF liquid lithium target: CFD calculations

CFD (Computational fluid dynamics) calculation turns out to be a good approximation to the real behavior of the lithium (Li) flow of the target of the international fusion materials irradiation facility (IFMIF). A three-dimensional (3D) modelling of the IFMIF design Li target assembly, made with the CFD commercial code ANSYS-FLUENT has been carried out. The simulation by a structural mesh is focused on the thermal-hydraulic analysis inside the Li jet flow. For, this purpose, the two deuteron beams energy deposition profile is modelled as an energy source term inside the volume of liquid affected. Turbulence is estimated using the RNG k– ɛ model, and a surface-tracking technique applied to a fixed Eulerian mesh called volume of fluid (VOF) is used to determine the position of the free surface. Calculations varying the jet velocity from a range of 10–20 m/s, show that maximum calculated temperatures are still below the lithium's boiling point, due to the increase of the pressure induced by centrifugal force.

Status of engineering design of liquid lithium target in IFMIF-EVEDA

In International Fusion Materials Irradiation Facility (IFMIF), intense neutron flux (4.5 × 10 17 n/m 2 s) with a peak energy of 14 MeV are produced by means of two deuteron beams with a total current of 250 mA and maximum energy of 40 MeV that strike a liquid Li target circulating in a Li loop. Major design requirement is to provide a stable Li jet at a speed of 10–20 m/s with a surface wave amplitude on the Li flow less than 1 mm for handling of an averaged heat flux of 1 GW/m 2 under a continuous 10 MW deuterium beam deposition. The target system consists of a target assembly, a replaceable back-plate, a Li main loop and a Li purification loop. In July 2007, Engineering Validation and Engineering Design Activities (EVEDA) started under Broader Approach. In this paper, status of the engineering design of the IFMIF Li target system performed in 2007/2008 is described. The future EVEDA tasks to develop the target system are also summarized.

Latest design of liquid lithium target in IFMIF

This paper describes the latest design of liquid lithium (Li) target system in International Fusion Materials Irradiation Facility (IFMIF). IFMIF is an accelerator-driven intense neutron source for fusion reactor materials testing. Two 40 MeV deuteron beams with a total current of 250 mA strikes a liquid Li target circulating in a Li loop. The Li target is to provide a stable Li jet at a speed of 10–20 m/s to handle an averaged heat flux of 1 GW/m 2. A concaved Li flow is applied to avoid Li boiling. A cold trap and two kinds of hot trap are applied to control impurities (T, 7Be, C, O, N) below permissible levels. A back wall made of RAFM is located in the most severe region of neutron irradiation (50 dpa/year). System availability requires more than 95% during plant lifetime. EVEDA tasks including Li loop are now being performed under the Broader Approach.

Numerical analysis of free surface instabilities in the IFMIF lithium target

The International Fusion Materials Irradiation Facility (IFMIF) uses a high speed (10–20 m/s) lithium (Li)-jet flow as a target for two 40 MeV/125 mA deuteron beams. The major function of the Li target is to provide a stable Li jet for the production of an intense neutron flux. Different hydrodynamic instability mechanisms are possible in the Li-jet flow. The main objective of this study is to provide a detailed numerical analysis of instabilities in the Li-jet flow caused by separation of the flow near the nozzle outlet. Experimental observations have shown that the change of the nozzle geometry at the outlet or nozzle edge defects causes the flow separation and occurrence of longitudinal periodic structures on the free surface. Target surface fluctuations of large magnitude can lead to the penetration of the deuteron beam in the target structure and cause the local overheating of the back plate. This work is focused on the validation the CFD code Star-CD and choice of the suitable simulation technique for further calculations of lithium target flow. Two simulation methods, Large Eddy Simulation (LES) and Reynolds Averaged Navier–Stokes method using the Shear Stress Transport (SST) turbulence model have been validated against the experimental data. Two experimental cases with two different kinds of instability sources were used to test the suitability of turbulence models to predict waves generated near the nozzle edge. While in the first case the instability source is a stationary located obstacle at the nozzle edge, in the second one the position of the instability sources is influenced from turbulent fluctuations in the boundary layer near the nozzle edge. LES has a reasonable agreement with experimental data. SST turbulence model is not able to predict the local flow separations at the nozzle edge caused by turbulence fluctuations and to reproduce instabilities of small magnitudes.

Investigation of free-surface fluctuations of liquid lithium flow for IFMIF lithium target by using an electro-contact probe

In the international fusion materials irradiation facility (IFMIF), 14 MeV neutrons will be generated by 40 MeV deuteron beam injection into a high-speed liquid lithium (Li) plane jet, flowing along a vertical concave wall in vacuum. The Li jet has to be stable to produce a stable neutron field, while a free surface flow is anticipated to be unstable. In order to ensure a reliable operation, a detailed knowledge of the Li flow is of conical importance. The experiment on the Li flow is conducted using the Li loop facility to qualify the magnitude of the surface oscillation. The test section of this loop, which is a 1/2.5 scale of the IFMIF design, produces a flat plane jet of 10 mm in depth and 70 mm in width with a free surface in the velocity range of up to 15 m/s. In the present study, a surface-detection apparatus called electro-contact probe, is employed. This apparatus allows us to measure the surface oscillation directly. By means of the electro-contact probe, the magnitude of the surface oscillation in this configuration was found to be in the range from 2.2 to 2.9 mm at the position of 175 mm downstream from the nozzle exit at a mean velocity of 15 m/s. This is the first time it was measured in detail. These values are considered to be improved in the case of the actual target of IFMIF. Estimation shows the present data of 2.9 mm could be transformed to be much smaller value, if the flow is free from the effect of surface wakes.

Activities on IFMIF lithium target at ENEA

The status of R&D activity ongoing at ENEA on the lithium target system of the international fusion materials irradiation facility (IFMIF) is reported. The activity has been launched in year 2000 in the frame of IFMIF key element technology phase in order to reduce the key technology risk factors and to guarantee the required availability and reliability of the IFMIF liquid Li target system. The items discussed in the paper are related to the Li jet flow stability numerical analysis, water flow simulation experiment, backplate remote handling simulation and Li target safety analysis.

Liquid lithium target under steady state ultra high heat load of 1 GW/m 2 range for International Fusion Materials Irradiation Facility (IFMIF)

International Fusion Materials Irradiation Facility is an accelerator-based neutron source using the D–Li stripping reaction to provide high intensity neutron field with energy of 14 MeV and damage dose rate of around 20 dpa/year for fusion materials development. To handle the intense deuterium beam power up to 10 MW which corresponds to ultra high heat flux of 1 GW/m 2, the liquid Li jet flow with a maximum velocity of 20 m/s and a concave flow configuration is necessary. According to thermal–hydraulic analysis, an induced centrifugal force with a radius of concave back wall (25 cm) realized that the Li temperature is lower than the Li boiling point. To confirm the hydraulic characteristics of Li flow, water jet simulation experiment has been done. Moreover, validation experiment in Li loop is under way in Osaka University. In addition, a permissible heat load of the Li flow under a surface heat deposition has been discussed.

Neutron irradiation characteristics in international fusion materials irradiation facility

Neutron field and damage parameters for the planned international fusion materials irradiation facility (IFMIF) were estimated for use in developing an irradiation configuration plan using this facility. The facility generates fusion-like neutrons using d—Li reactions with 30–40 MeV and two 125 mA deuteron beams with an angle of 10°, and with a Li jet target with a square beam spot of 50 mm × 200 mm in typical size. The analysis was performed for four standard sample loading models, consisting of Fe or SiC for test materials and NaK or He for coolant. The calculation was carried out by the Monte Carlo code GMVP with the HILO/86-J3 library with the external source obtained from an analytical model. The flux—volume relation was obtained together with the relation of the dpa rate—volume. The dpa—He gas production ratio and nuclear heating were also estimated inside the standard samples.