MAXSIMA Deliverable D3.9 CFD simulation of the safety/control rod system in the MYRRHA configuration

In the framework of the MAXSIMA project, the dynamics of the MYRRHA Control Rod (CR) system is simulated, in the conditions of the COMPLOT experimental facility upgraded to the MYRRHA configuration by including the free surfaces. The model was upgraded with the inclusion of the free surfaces in the buffer tank, representative of the cold plenum, and in the guide tube, representative of the hot plenum. The transient behavior of the full scale control rod in a flowing Liquid Bismuth Eutectic (LBE) environment is simulated by CFD means. The insertion must be performed in less than 1s, under the influence of the buoyancy and of the rising flow. The CR is slowed down by means of a damper which forces the fluid through a series of discharge slots. The original geometry of the fluid path is modeled with high fidelity, while some simplifications are made for the moving component. The 3D-CAD geometrical model was constructed autonomously according to the definitive COMPLOT design, including the 19-pin bundle, the main part of the moving component and the most demanding in terms of computational costs. Suitable boundary conditions for the steady state and transient simulations are determined. The overset mesh methodology implemented in STAR-CCM+ reached sufficient maturity and allowed the entire CR displacement to be simulated. The method is applied to reproduce the CR motion, with several preliminary simplifications and gradual increased geometrical accuracy. In phase of testing and improvement of the various numerical tools, the displacement is imposed, according to 1D theoretical calculations. More representative two-way coupling motion simulations, with the displacement inferred by Newton law from the force balance on the CR, have been performed. The numerical methodology and the results are illustrated and discussed; the comparisons with the experimental test results show good prediction of the time insertion and behavior of the control rod.

@TechReport{PM16,
  author       = {Profir, M. and Moreau, V.},
  title        = {MAXSIMA Deliverable D3.9 CFD simulation of the safety/control rod system in the MYRRHA configuration},
  institution  = {CRS4},
  month        = {november},
  year         = {2016},
  type         = {European project Deliverable},
  keywords     = {Numerical simulation, nuclear safety, free surface, control rod, overset mesh},
  url          = {https://publications.crs4.it/pubdocs/2016/PM16},
}