Tritium-breeding self-sufficiency of DEMO reactors with a water-cooled Pb17Li blanket

In the frame of the studies developed for DEMO breeding blankets, a type of blanket with Pb17Li as breeder and water as coolant has been developed at the JRC-Ispra. It deals with breeder circular modules, intemally cooled by water in U-type tubes and arranged poloidally according to rows inside boxes, named segments. A 3-D neutronic analysis of the DEMO reactor with this blanket configuration has been performed, to verify if tritium breeding self-sufficiency could be achieved without the need of additional multipliers. The DEMONET specifications have been applied, and the MCNP-3B Monte-Carlo code has been used. A careful modelling of the compIicated blanket Iayout has been carried out, avoiding where possible homogenization procedures. A total Tntium Breeding Ratio (TBR) of 1.152 is obtained as a final result of the MCNP run. If the presence of the ports is considered, a net TBR of 1.09 is achieved. It is therefore verified that this blanket permits to achieve self-sufficiency without any additional multiplier. The results of this analysis are critically compared with previous ones, which used 1-D models and approximated expressions to estimate the net TBR. A good agreement between the two studies is found out.