## 3 WCLB BB Performance
### Neutronic Performance  
In order to assess the neutronic performance of the WCLL BB, three-dimensional coupled neutron and gamma transport simulations have been performed [16] by means of the MCNP5v1.6 Monte Carlo code and the Joint Evaluated Fusion File JEFF 3.3 nuclear data libraries, according to guidelines on neutronic studies. The analyses, carried out while adopting a fully heterogeneous model of the DEMO WCLL BB, mainly concerned the assessment of the TBR and shielding performance. According to the latest recommendations, the total TBR should be at least 1.15 [23]. This design target was set to guarantee the necessary tritium generation to sustain a reactor while considering the impact of the in-vessel components that reduce its generation (e.g., penetrations for diagnostic or plasma heating systems) and losses due to the radioactive decay of tritium, as well to provide the start-up inventory for a follow-up D-T power plant. On the other hand, the blanket should ensure that the damage on VV steel, accumulated over the lifetime of DEMO (equivalent to 6 FPY), is below 2.75 dpa. Furthermore, the He concentration should be below 1 appm in re-weldable zones. The protection of the superconductive TFC is one of the most critical issues in the design of the BB: an evaluation of the fast neutron flux on the superconductor coils (design target: \(<\)10\({}^{9}\) n/cm\({}^{2}\)/s) and the estimation of the nuclear heating due to neutrons and gammas deposited on the winding pack (design target: \(<\)5 \(\times\) 10\({}^{-5}\) W/cm\({}^{3}\)) can provide a reliable verification of the WCLL BB's shielding efficiency [24]. The MCNP DEMO model integrating the WCLL blanket was used to assess the nuclear performance of the WCLL DEMO BB, and results were normalized to 1998 MW fusion power (neutron yield: 7.095 \(\times\) 10\({}^{20}\) n/s). The poloidal distribution of the neutron wall loading (NWL) was estimated for the inboard and outboard segments; maximum values were reached in the outboard and inboard equatorial zones (1.33 and 1.1 MW/m\({}^{2}\), respectively), while the poloidal average was 0.93 MW/m\({}^{2}\). The verification of the tritium self-sufficiency for the WCLL DEMO reactor was carried out through the assessment of the total TBR by means of track-length (F4 tally) with proper tally multipliers (FM card) for each component of the BB that contributes to tritium generation while considering both neutron capture reactions on \({}^{6}\)Li and \({}^{7}\)Li isotopes. The resulting total TBR for this configuration was found to be 1.15, so the design target for tritium self-sufficiency was satisfied: 69.7% of the tritium was produced in the outboard sector, while 30.3% was generated in the inboard. A breakdown of the nuclear power deposition due to neutrons and secondary gammas in the WCLL blanket components is provided in Table 1. The total nuclear power deposited in the BB system was 1716 MW: in particular, about 78.2% was found to be deposited in the BZ, manifolds, BSS, and caps; about 18% was deposited in the FW and side-walls; and about 3.8% was deposited in the W armour. Moreover, most of the power (70.3%) was deposited in the outboard region. Finally, it has to be considered that this nuclear heating value had to be normalized to the required TBR (TBR\({}_{\text{req}}\)), which is presently equal to 1.05 [23]. Indeed, since the current neutronic model does not consider penetrations due to auxiliary systems, the tentative requirement for the TBR design target (TBR\({}_{\text{tar}}\)) was increased up to 1.15, where it stands currently [23]. Considering these assumptions, the effective nuclear heating value deposited within the BB was found to be equal to 1566.12 MW (1716 MW \({}^{*}\) TBR\({}_{\text{req}}\)/TBR\({}_{\text{des}}\)). Obviously this evaluation needs to be assessed in detail in future neutronic analyses that adopt a detailed model of the in-vessel components (BB, divertor, and auxiliaries).