## 2 WCLL BB Layout  
The design of the breeding blanket is strongly influenced by the DEMO reactor layout. The current DEMO configuration [5] includes 16 TFCs that basically divide the whole machine into 16 sectors of 22.5\({}^{\circ}\). Each sector is further split in five BB segments, two in the inboard region--namely left and right inboard blanket segments (LIB and RIB, respectively)--and three in the outboard region--namely left, central, and right outboard blanket segments (LOB, COB, and ROB, respectively).  
The WCLL BB architecture experienced a deep revision process during Horizon 2020 or European Framework Program 8 (FP8) [6]. The original design was mainly based on an ITER-like concept, namely a blanket segmented in several \"small\" modules whose dimensions were roughly 2 m in the poloidal direction, 1 m in the radial direction and 1.5 m in the toroidal direction [7; 8; 9; 10; 11]. This concept is better known as multi-module segment (MMS). Consequently, following the adoption of a new DEMO architecture in 2017 [5; 12; 13], the reference BB design moved from the MMS to the single-module segment (SMS) concept. Indeed, this layout allows one to: (i) optimize the shielding performance and increase the tritium breeding ratio (TBR) thanks to the absence of gaps between the different modules in the poloidal direction, (ii) increase the robustness of the segment against high electromagnetic (EM) loads derived from possible plasma disruptions [14], and (iii) simplify the distribution of both the breeder and coolant to the different regions of the blanket.  
A generic WCLL-BB segment can be considered to be composed of five main regions: (i) the First Wall-Side Wall (FW-SW), a U-shaped and actively cooled plate mainly used to face the plasma; (ii) the breeding zone (BZ), the area where breeding reactions take place; (iii) the manifolds, a region where the process fluids are distributed and re-collected; (iv) the back supporting structure (BSS), a backbone structure with the main duty of withstanding mechanical loads and assuring the BB's connection with the VV; and (v) the caps, two actively cooled plates that close the segment in the poloidal direction. An \"exploded\" view of the COB segment is shown in Figure 1.  
Concerning the process fluids, three independent loops are needed: one is used to circulate the PbLi eutectic alloy and two are used to route the water coolant. Indeed, the FW-SW structure and the BZ are cooled by water flowing into two separate systems at the same thermo-dynamic conditions. In particular, water coolant circuits are at set to a pressure of 15.5 MPa, with the water temperature ranging from 295 to 328 \({}^{\circ}\)C. Concerning the PbLi, it is assumed to that it does not remove any thermal power, remaining isothermal at a temperature of about 330 \({}^{\circ}\)C. An average pressure of 0.5 MPa occurs, though it considerably varies along the poloidal abscissa of the segment due to the non-negligible liquid metal. Fluids are delivered to and removed from the BB by means of feeding pipes routed through both the lower and upper ports. Lead-lithium is fed through the lower port and extracted from the upper one, whereas cooling water is fed and extracted from the upper port.