Thermal–hydraulic analysis of the HCLL DEMO blanket

The present design of the helium-cooled lithium-lead (HCLL) blanket foresees the successive cooling of three sub-components (the first wall, the stiffening grid, and the breeder cooling plates) by parallel He-cooling channels. The optimisation of the coolant flow is complicated by the fact that the heat recovered by the cooling elements depends on the coolant parameters (temperature, velocity, heat exchange coefficient). Since all these parameters are intrinsically related, the classical approach of obtaining the coolant temperature distribution by enthalpy balance and using this distribution as an input for finite element analyses cannot be used. In this paper we present new finite elements models of the blanket that allow to obtain the temperature distribution in the coolant on the basis of the detailed power density distribution in the surrounding structures. At the same time, the models allow to improve the description of the heat transfer between the solid walls and the coolant. A review of the most used correlations available in literature to estimate the heat transfer coefficient has then been performed and the most appropriate one has been selected. The new models have been used to carry out a thermal–hydraulic analysis of the cooling system of the HCLL breeding blanket. Moreover, an estimation of the pressure drops in the different cooling elements has been made. The obtained results are discussed in terms of differences with those obtained in previous analyses and of the consequences on the blanket design.