Proof-of-principle of the control rod emergency insertion in the MYRRHA nuclear facility from a combined numerical-experimental campaign

This paper presents the combined numerical-experimental investigation campaign of the buoyancy driven MYRRHA control rod (CR) insertion during an emergency SCRAM, aimed to demonstrate its proof-of-principle. A full-scale mock-up test section of the MYRRHA CR was constructed to test the hydrodynamics in Lead Bismuth Eutectic over a wide range of operating conditions providing experimental data for the qualification of the CR system. A numerical CFD model of the CR test section was also setup in STAR-CCM+ for pre-test and post-test analysis. Numerically, the CFD model requires the application of the overset mesh method in an extremely constrained domain. The CR acceleration arises from Newton's law but also strongly affects the surrounding flow pressure, requiring a two-way coupled solution of the CR motion and the fluid dynamics. The CR dynamics are also controlled by distant boundary conditions which requires the inclusion of several free surfaces. The COMPLOT test section is described together with its numerical counterpart. The procedure and the methods used to reach the CR numerical two-way coupling motion are explained. The numerical results are compared with the experimental results. (authors)