# Neutronic Activity for Development of the Promising Alternative Water-Cooled DEMO Concepts
###### Abstract
Liquid lead being used as a neutron multiplier is widespread and not expensive. Weak points in the WCLL blanket concept are corrosion between PbLi eutectic and steel structure, a tritium permeation from PbLi through steel walls in the water coolant, and an immature tritium extraction technology. These technological issues are out of the scope of this work, and they are not addressed in the paper. A solid breeder used in the HCPB blanket provides efficient tritium generation, and its extraction from the helium purge gas is technologically feasible and industrially scalable. The main disadvantages of the HCPB blanket are the cost of the neutron multiplier (Be\({}_{12}\)Ti) and a high-pressure (80 bar) helium primary cooling loop that assumes a ramified pipe system and big heat exchangers. The research efforts in the WCLL blanket developments are concentrated on alternative solutions to improve its efficiency, safety, and reliability. This assumes the development of new schemes of the blankets layouts using basically the same materials but leading to more efficient tritium generation and also to the higher energy deposition in the blankets. To this end, an alternative and promising design was proposed and elaborated for the WCLL concept enabling it to meet the requirements for the efficient blanket design discussed above. This concept, WCLL-db (WCLL-double bundle) [5], can potentially provide a more rational use of the blanket volume for tritium generation compared to the reference WCLL design. A promising solution for the blanket design could also be potentially gained as a combination of the benefits of the driver blankets concepts: (1) the use of the solid breeder for the tritium generation, (2) the liquid lead neutron multiplier, and (3) pressurized water coolant. This WLCB (Water-cooled liquid Lead Ceramic Breeder) concept represents a trial to replace a very expensive Be\({}_{12}\)Ti neutron multiplier used in the HCPB breeder blanket concept with the less effective but much cheaper Pb one to solve a problem with a Be supply for DEMO needs. Such breeder blankets would have the potential to operate in two modes: with and without liquid lead circulation. The former is similar to the operation scenario of the reference WCLL DEMO blanket, and the latter assumes the blanket without liquid metal circulation in the external loop. The second option is much more attractive from the DEMO design point of view: it saves reactor space and makes the whole project significantly cheaper. However, a choice between these options could be made only after detailed nuclear, thermal, and safety analyses. This paper presents an assessment of the main nuclear responses of the WCLL-db and WLCB breeder blankets necessary to support R&D work aimed at a consolidated blanket design. Such activity assumes the implementation of several work steps with a final goal of developing a suitable geometry model of the DEMO with breeder blankets arranged in the plasma chamber and carrying out numerical simulations. This procedure is well-established and implies a logical sequence of the developments and research activities providing robust geometry models that ensure high-fidelity results of the neutronic simulations. The workflow has several milestones: development of the CAD geometry model for the blankets, conversion of these models into an MCNP geometry representation, elaboration of the MCNP input deck, MCNP simulations, and analysis of the results.