# Neutronic Activity for Development of the Promising Alternative Water-Cooled DEMO Concepts
## 3 WLCB Blanket Study
### Results of the Neutronic Simulations for the WLCB DEMO  
The MCNP calculations were carried out for the WLCB DEMO in the same way as for the WCLL-db one. Because the WLCB blanket project development is at an early beginning step, the first nuclear response required for the design maturity assessment is its tritium breeding performance, TBR. For the initial blanket configuration, Figure 9, the very low TBR was calculated, TBR = 1.05. To find the direction for further geometry modifications, the size of the smallest tubes with the breeder ceramic in the front part of the breeder zone was increased from R = 6 mm to R = 16 mm, Figure 10. For this modification, the tritium breeding performance of the WLCB blanket is still low compared to the TBRreq, TBR = 1.08. The arrangement of the additional poloidal breeder tubes in the rear part of the breeder zone does not contribute noticeably to the TBR. Figure 8: Poloidal segmentation of the breeder blanket (**left**) and a vertical cut of the MCNP model on the OB side. Figure 9: Horizontal cuts of the WLCB MCNP model in the IB (**left**) and OB (**right**) sides. The insufficient tritium breeding capability of the WLCB blanket can be improved within the optimization procedure used to achieve a reasonable TBR value. The variation technique can be applied not only to the geometry dimensions but also to the general layout of the breeder zone, assuming either the poloidal or radial arrangement of the breeder-containing cells. The former one is suitable for the vertical Pb flow stimulated by gravitational force, and the latter one provides similar irradiation conditions for the breeder ceramic enclosed in the cells from the same toroidal row. Presented in Table 3 are the horizontal and, when necessary, vertical cuts of the outboard blanket for different BZ layouts: two WLCB geometry layouts with poloidal, two ones with radial arrangements of the breeder tubes, and the one case with the breeder ceramic enclosed in the vertical plates. In all cases, pressurized water with 155 bar is used for the FW and breeder zone cooling. Case #1 assumes three rows of the small poloidal tubes (\(\mathcal{O}\)18 mm) in the front region of the BZ and 11 rows of the bigger tubes (\(\mathcal{O}\)26 mm) in the rear part of the BZ. A 3 cm thick stiffening plate behind the breeder tubes separates the BZ into two parts, and it ensures the integrity of the blanket. The rear part of the BZ behind the separating stiffening plate is filled with a 2 cm neutron graphite layer and massive breeder ceramic blocks. This structure is placed between two vertical cooling plates of 7 mm thickness (50% water/50% steel), and it is repeated in the toroidal direction with the 123 mm step. The vertical disposition of the breeder tubes is also adopted in case #2, Table 3. For the same dimensions as the BZ unit, the breeder tubes have two annular regions: inner (\(\mathcal{O}\)40 mm, 1 mm steel wall) with water coolant and outer (\(\mathcal{O}\)83 mm, 1.5 mm steel wall) with breeder ceramic. The cooling plate is similar to case #1. In the rear part of the BZ (35 cm), liquid lead is replaced with graphite filler. The tritium breeding capability of the WLCB in the #1 and #2 cases TBR\({}_{90}\) = 1.12 and 1.11, respectively. An index of 90 in the TBR\({}_{90}\) indicates 90% enrichment of \({}^{6}\)Li in the breeder ceramic. The radial integration of the breeder pins in the BZ is presented in cases #3 and #4, Table 3. For these variants, both radial and vertical cuts of the OB blanket are shown in the table. The BZ units have the same toroidal size, 123 mm, similar to cases #1 and #2. The breeder pins are arranged in horizontal rows with a pitch of 31 and 38 mm in cases #3 and #4, respectively. The pins have the central He purge gas channel (\(\mathcal{O}\)4 mm in case #3 and \(\mathcal{O}\)8 mm in case #4) and the annular breeder ceramic layer (\(\mathcal{O}\)26 mm in case #3 and \(\mathcal{O}\)38 mm in case #4). The 7 mm thick steel/water stiffening plate protects a toroidal deformation of the FW.