## 2 Geometry of Technological Solution  
Water treatment requires low-energy, high-power accelerators. The lower the electron beam energy, the lower the penetration of the wastewater stream that sets the technological requirements regarding the low liquid thickness [31]. Therefore, different geometry technological solutions and special injection nozzles are applied to ensure the appropriate thickness of the irradiated layer and the effective and homogeneous irradiation of the wastewater stream (Figure 1). The first kind of wastewater stream configuration (Figure 1A) is the most common as the solution characterized with perfect displacement. A continuous wastewater jet with the width adjusted to the scanning width of the accelerator is formed by a nozzle injector. After irradiation by a transverse electron beam, wastewater is collected below in a tray. The thickness of the irradiated layer of wastewater is correlated with the penetration of accelerated electrons which depends on accelerator energy [32]. Irradiation of either falling film or up-flow mode or injected wastewater stream ensures the most efficient EB utilization [16]. Thus, in case of water and wastewater treatment plants equipped with EB accelerators selected parameters of the electron beam, energy of electrons and beam power, for the water or wastewater treatment influence design of pre-treatment steps, under beam system, shielding of irradiation chamber and also economical reliability of installation. In the presented study, it was estimated that the optimal parameters of the beam, reducing investment and operating costs, and at the same time providing sufficient penetration of electrons in treated medium at the required dose rate, will be reached using the transformer  
Figure 1: Different geometry of stream configuration for wastewater irradiation: (**A**) jet injection, (**B**) two opposite jets injection, (**C**) sprayer, (**D**) up-flow system with air bubbling, (**E**) natural flow. accelerator characterized with 50 kW beam power and electron energy level 800 keV. A very important step in the construction of the installation of the wastewater EB treatment plant is the design of an irradiation chamber to house the electron accelerator. The geometry and weight of the shielding play key roles in this design. The need of design guidance in shielding construction that allows to determine the minimum shielding requirements and reduce the cost of the whole installation has been signalized [16]. The wastewater treatment EB plants previously tested and operated [33; 34] have been constructed on land and shields were made of heavy concrete (magnetite admixture) or steel-reinforced concrete. No special attention was paid to the construction of the under beam system, which led to high intensity X-ray radiation. This phenomenon is called Bremsstrahlung, an electromagnetic radiation produced by the deceleration of a charged particle when deflected by another charged particle, typically an electron by an atomic nucleus, which yield is increasing with the energy of electrons and the atomic number of material hit by electrons.. The dose rate in the electron beam process chamber is extremely high compared to the natural background. Industrial accelerators are capable of delivering a dose rate of several kGy per second, while tolerable background radiation can be as low as 0.1 uGy/h. For this reason, an irradiation shield is required to attenuate radiation by a factor of 10-12 (bremsstrahlung) in order to protect personnel and the environment [34]. Another factor is the cost of such a shielded room applied, which represents 1.5-2 million USD [35]. It must be taken into account that not each EB installation can be shielded and using different concrete shielding materials can also be applied. In case of limited space, steel can be used, and with its density of about 7.8 g/cm\({}^{3}\) it can significantly reduce the thickness of constructed shielding.