# Nuclear Analysis of High-Power LIEBE Molten Target at CERN for the Production of Radioisotopes
## 3 LIEBE Target Model and Conversion  
At present, LIEBE is a prototype liquid metal ion beam target (see Figure 1) aimed at solving issues of accommodating a high-power beam and ensuring adequate extraction of short-lived radioisotopes [2]. Liquid target material circulates through different functional components of the target-irradiation chamber, diffuser and heat exchanger. LIEBE uses a lead-bismuth eutectic (LBE) circulating in a 200 \({}^{\circ}\)C-600 \({}^{\circ}\)C temperature loop. The eutectic is driven by an electromagnetic pump to an irradiation chamber, where it is subjected to the high-power proton beam. The irradiation chamber has a length of 210 mm and a width of 10 mm. The proton beam enters the chamber through the half-cylinder-shaped window. Chamber itself is  
Figure 1: CAD model of the LIEBE target (1—electromagnetic pump, 2—irradiation chamber, 3—diffusion chamber, 4—heat-exchanger, the arrow shows the beam direction). separated into three parts by two internal feeder grids. These two intermediate grids are devised to improve profiles of LBE flow velocities. They should develop a more uniform flow evacuation-velocity distribution at the chamber exit. Irradiated eutectic then falls through a grid separating irradiation and diffusion chambers. This grid is intended for the shower formation--it should fragment falling LBE into 0.4 mm diameter droplets, which would then fall along the height of the diffusion chamber. The diffusion chamber is designed to accommodate the fast extraction of radioisotopes from falling metal droplets. Such a design is needed to enable the extraction time of short-lived isotopes faster than their half-lives. A high-power proton beam will deposit a large amount of excess heat to the circulating eutectic. To remove the excess heat, eutectic will flow to the water-cooled heat exchanger from the diffusion chamber. The LIEBE device, presented in Figure 1 is encapsulated inside a container with an argon atmosphere, to prevent air exposition and oxidation of the liquid LBE [3]. The first milestone of the study was the creation of a calculation model. To achieve this, a recent CAD model of the LIEBE target was used. Therefore, the production of the MCNP input file required the conversion of the CAD model to a 3D description of the MCNP geometry. This was achieved in the SALOME environment [10] using the McCAD [11] conversion tool, which is a Monte Carlo CAD-based modeling program used to convert CAD drawings to the geometries of MCNP, TRIPOLI [12] and Geant4 [13] codes. With the help of the code, the available CAD model was decomposed, i.e., divided by all geometry surfaces and converted to MCNP format. Due to the complex and detailed nature of the existing CAD model, automated conversion was hardly possible, requiring individual manual modification of many components. The conversion process involved several challenges. These are caused by the fact that certain parts of the CAD model do not have an MCNP counterpart in the geometry description. In Figure 2, the detected problem areas of the CAD model are presented, i.e. spline (surfaces defined by control points) and torus surfaces whose axes of revolution are not perpendicular to any of the \(x\), \(y\) or \(z\) axes. The problematic areas had to be converted into basic surfaces: cylinders, planes and perpendicular to \(x\), \(y\) and \(z\) planes tori. The conversion was achieved using the SALOME software McCAD module. Since the CAD model of the LIEBE target was complex and detailed, many elements of the model also needed to be manually simplified. These modifications were primarily spline and torus surface approximations with cylinders and planes (as in Figure 3). Figure 2: Problematic areas (red and orange colors) of LIEBE target CAD model. The most complex LIEBE component was the heat exchanger and its component tubes (see Figure 4), which was approximated by a rectangular prism of a water-steel mixture.