A heavy ion accelerator uses a liquid lithium film as a charge trap to increase the acceleration efficiency of uranium. Uranium ions with a charge of 33+–34+ become uranium ions with a charge of 79+, passing through the liquid lithium film with a thickness of 22 µm. The liquid lithium thin film is developed by collisions between a liquid lithium jet and a flat deflector.
The analysis was carried out to optimize the charge stripper device using simulation and water jet experiment in the aspect of liquid lithium film thickness. The MHD circulation system is adopted to circulate liquid lithium because it has mechanical safety and precise pressure control. The liquid lithium film experiment was carried out with analyzed results and manufactured MHD circulation system.
The lithium charge harvester device is optimized by controlling the position of the deflector and adjusting the input current.
Introduction
The MHD circulator that converts the electromagnetic force into the Lorentz force amplifies the defects of liquid lithium. The liquid film of lithium that removes the charge from the uranium is made by a jet system. Electrons are removed from the thin film of liquid lithium as the uranium bundle flows from left to right as shown in Fig.
The lithium charge stripper with MHD circulator can continuously strip the charge without worrying about corrosion problems compared to a solid fossil system [8, 9]. The required specification of liquid lithium film thickness can be calculated as thickness divided by the density of liquid lithium. Therefore, charge harvester optimization was made to create liquid lithium film thickness of 22 µm adjusted with the deflector geometry, nozzle diameter, nozzle angle and input current of the MHD circulator.
Literature survey
Types of MHD circulator
Induction MHD circulators can be distinguished by the method by which they create a magnetic field. They are divided into moving magnet induction MHD circulators, which produce an advancing magnetic field in the form of a moving permanent magnet, and stationary magnet induction MHD circulators, which use a fixed electromagnet. Stationary magnetic induction MHD circulators are further divided into three-phase and single-phase induction MHD circulators depending on the number of phases of the input current [10, 14].
MHD circulator development history
The direction of Lorentz's force is the vector product of the current and magnetic field [29]. The component of the electric field was ignored due to the symmetry of the helical-type MHD circulation system. The magnetic flux density in the flow channel was analyzed by applying the magnetic coercivity of the permanent magnet (Sm2Co17) and magnetic permeability of the ferromagnet using finite element method (FEM).
The water nozzle experiment was used to cover the limitation of the liquid lithium experiment as shown in Fig. In the case of an internal ferromagnet, the increase in the magnetic flux density was less than 110 mm as shown in Fig. The average magnetic flux density of the MHD circulator was 0.6 T when the ferromagnet was added to the magnet as shown in Fig.
The thickness of the thin film was proportional to the flow rate shown in Fig.
State-of-the-art lithium charge stripper
Methods
Simulation method
- Finite element method
- Equivalent circuit equation
The divergence of the total magnetic flux density was zero, and that of the external magnetic flux density from the permanent magnet was zero. The current density in the θ direction was zero because the electric field in the θ direction and the vector product of the velocity and the magnetic flux density in the θ direction were zero. M⃗ = χ The total magnetic flux density in the helical MHD circulator system was calculated using Eq. 3.1.31) by considering the permanent magnetic field and the independent local magnetic field with the relative permeability (μ.
0 (3.1.34) The tangential component of the magnetic field intensity (Ht) and the normal component of the magnetic flux density (Bn) between high- (low carbon steel) and low-magnetic permeability materials air, stainless steel 316L, C103, and Sm2Co17) at the interface was applied to solve the magnetic flux density and flux line in the helical-type MHD circulator system using the ANSYS electromagnetic code simulation. The vector product of the current density in the z direction and magnetic flux density in the r direction can be ignored in contrast to the current density in the r direction and magnetic flux density in the z direction. The induced magnetic flux density in the r and z directions could be ignored because the electric field in the r direction was negligible.
Therefore, the pressure gradient in the Navier–Stokes equation can be expressed as the current density multiplied by the magnetic flux density.
Experimental method and setup
- Water nozzle experiment
- MHD circulator experiment
- Thickness measurement
The lithium storage tank stores lithium when the system is not operating, and the charging stripper ejects liquid lithium from a thin nozzle by driving the MHD circulator installed in the circulation system. Previous technology measured the thickness of thin liquid lithium film with an electron gun, but using such a gun requires radiation licenses. Two lasers are installed to measure the distance between the laser and the film; they make it possible to measure the thickness of the film by distance differences.
It has the drawback of a short range problem; to overcome this, changing the geometry of the load remover was carried out as shown in Fig. Holding the load stripper was a sight to observe the status of the liquid lithium film, the deflector and nozzle helped to create the liquid lithium film, the level gauge the flow rate of the MHD circulator, the equivalent line helped to ensure the pressure of equal to the storage tank and quartz was used to measure the laser system.
Results and discussion
MHD circulator
- Feature analysis
- Newly designed MHD circulator
- Experimental characterization
The magnetic flux density is maintained constant and increases when a z-direction magnetizing magnet is added due to the perpendicular direction of the magnetic flux in the z-direction magnetizing magnet. However, its decrease was recorded after 110 mm due to the increase of the distance with magnets. The magnetic flux density according to the thickness and height of the outer ferromagnet converged to 40 mm and 440 mm, respectively, due to the limited magnetic shielding as shown in Fig.
There are three pressure mechanisms of the MHD circulation that generate pressure due to the Lorentz force and pressure loss from the electromotive force and hydraulic friction. The changing geometry of the magnet and channel was carried out for maintenance, as shown in figure. The drawing of the new MHD circulator includes an electrode for delivering current, a bracket for mounting, channel, magnet and core as shown in figure.
The flow channel structure of the MHD circulator can be easily replaced when unexpected circumstances arise. The oxidized surface of the lithium ingot floats when the feed tank is heated as shown in fig. The lithium feed tank has a sight opening that allows observation of the lithium melt situation and is connected to the loop system on a 3/8-inch pipe as shown in fig.
The test vessel consists of an inspection port to check the operation of the MHD circulation pump and a level gauge attached to check the system flow as shown in the figure. A control panel is added to the loop system to control the reservoir temperature and flow path as shown in Fig.
Charge stripper
- Water experiment prediction
- Design and Fabrication
- Liquid lithium experiment
The short length is unstable with respect to the displacement of the uranium beam at an angle below 30° shown in Figure 4.2.5, and the film was not formed horizontally and at an unstable angle above 38° shown in Figure 4.2.6. The obtained length of the lithium film was stable between 30° and 38°, so the average value of the angle was determined to be 34°. In order to know the characteristics according to the geometry of the deflector, the deflector was designed and manufactured as shown in fig.
The greater the curvature, the fewer points interfere with film formation, so the 50 mm size radius was determined as shown in Fig. Finally, the deflection of the deflector was 50 mm to avoid contamination at the lithium spot and the nozzle design was angled at 34° with a diameter of 0.7 mm to make a stable film of 22 µm thickness. The components of the charge stripper were nozzle, deflector, view port, laser quartz, level meter and argon equivalent line as shown in Fig.
The nozzle and deflector create the liquid lithium film by collision, and the viewport is used to control the conditions of the liquid lithium film. The laser passes through the quartz section and the level meter is used to monitor the flow rate of the system. The liquid lithium sprayed through the nozzle collided with the deflector and formed a thin film.
Consequently, an input current of 107 A was required to achieve a liquid lithium film thickness of 22 µm with a standard deviation of 4.3 µm to achieve an energy of 200 MeV/U.
Conclusion
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FRIB successfully circulates liquid lithium in charge stripper unattended for more than seven days.https://frib.msu.edu/news/2019/circulates-lithium-unattended.html. Magnetohydrodynamics approach to active decay heat removal system in future generation IV reactor. International Journal of Energy Research.
