Experiments on the MHD effect on the drainage of a LiPb channel and supporting numerical computations with the level set method

To analyse the impact of Magneto Hydro Dynamic effect on the drainage of LiPb channel in the WCLL BB (Water-Cooled Lithium-Lead Breeding Blanket) in case of fast-draining, it was carried out an experimental and numerical analysis with the support of the experimental facility IELLLO (Integrated European Lead Lithium LOop). IELLLO was designed and installed at ENEA Brasimone Research Centre, Italy, aiming to support the design of the WCLL and HCLL (Helium Cooled Lithium Lead) Breeding Blanket of the European DEMO fusion reactor. The Lithium-Lead Eutectic (LLE) aims to be used in the breeding blanket with the function of tritium breeder, neutron multiplier and tritium carrier. The interaction between the magnetic field and the liquid metal hinders the flow to be correctly described by classic Navier-Stokes equations. The electrically conducting liquid metal interacts with the transverse magnetic field generating a Lorentz force which strongly modifies the hydrodynamic profile of the flow. This principle is used also to pump the LLE; in particular, a Permanent Magnet Pump (PMP) was installed in IELLLO loop to realize the liquid metal circulation in the loop. In this frame, a model of the draining of the internal channel of the PMP pump, developed with COMSOL Multiphysics, is presented, and compared with a classical CFD solution. In this way, it was possible to evaluate the LLE velocity, the pressure field and the electric potential, in both the configurations, and to estimate the time gain due to the action of the magnetic field. The MHD discharge has been modelled implementing the Level Set Method (LSM) in order to describe the transient behaviour of the turbulent MHD flow under low-Re approximation, taking into account a finite wall electrical conductivity. The turbulence has been described by an SST model coupled with modified Navier-Stokes and Maxwell equations. The developed code has then been compared over the experimental results, where the time needed to fully drain the pump channel was measured. The case study presented can be considered as the first step in code validation for what regards transient and turbulent MHD flows.