Magneto-Convective Analyses of the PbLi Flow for the EU-WCLL Fusion Breeding Blanket

The Water Cooled Lithium Lead (WCLL) breeding blanket is one of the driver blanket concepts under development for the European Demonstration Reactor (DEMO). The majority of the blanket volume is occupied by flowing PbLi at eutectic composition. This liquid metal flow is subdued to high fluxes of particles coming from the plasma which are translated into a high non-homogeneous heat volumetric source inside the fluid. The heat is removed from the PbLi thanks to several water tubes immersed in the metal. The dynamics of the PbLi is heavily affected by the heat source and by the position of the tubes. Moreover, the conducting fluid is electrically coupled with the intense magnetic field used for the plasma confinement. As a result, the PbLi flow is strongly affected by the Magnetohydrodynamics (MHD) forces. In the WCLL, the MHD and convective interactions are expected to be comparable. Therefore, the PbLi dynamics and consequently the heat transfer between the liquid metal and the water coolant will be ruled by the magneto-convective phenomenon. This work presents 3D computational analyses of the PbLi flow in the frontal region of the WCLL design. The simulations include the combined effect of MHD forces caused by the magnetic field and the buoyancy interaction created by the temperature distribution. The latter is determined by the PbLi dynamics, the volumetric heat source and the position of the water tubes. Simulations have allowed computing the heat transfer between the PbLi and the water tubes. Nusselt and Grashof numbers have been obtained in the different regions of the system.

Fusion breeding as an approach to sustainable energy

This article examines an approach for sustainable energy called fusion breeding. This is the use of 14 meV fusion neutrons to breed fuel for thermal nuclear reactors. Currently thermal nuclear reactors use for fuel, only the isotope of uranium, 235U, which is 0.7% of the total resource. In order for nuclear power to be sustainable, it is necessary to breed nuclear fuel (233U or 239Pu) from fertile material (238U or 232Th). This resource could supply tens of terawatts for thousands of years. By any reasonable criterion, it both sustainable and carbon free. While most efforts at breeding envision fission reactors of one type or another, fusion is also a possible approach to breeding. Not only that, fusion has many advantages as a route for breeding that fission simply does not have. This article makes the case for fusion breeding.