NUMERICAL ANALYSIS OF MYRRHA CONTROL ROD SYSTEM DYNAMICS

This paper focuses on the CFD simulation of the MYRRHA Control Rod (CR) transient behaviour in a flowing LBE environment during a SCRAM emergency insertion. During normal operation the control rods are inserted in the LBE, below the active core. The high density of the liquid metal coolant allows buoyancy to be the driving force for the emergency insertion of the control rods during SCRAM, which must be performed in less than 1s. In the numerical model, the original geometry of the fluid path and the absorber pins bundle is modelled with high fidelity for the steady state simulations, while some simplifications are made for the moving component in the transient simulations. The adopted moving mesh techniques initially use automatic volume mesh adaptation with re-meshing of the underlying geometry and evolve naturally to the use of the more versatile overlapping grids. The overset mesh method applies well to complex flow paths, once the ability of handling small or zero gaps is acquired. The method is applied to reproduce the CR displacement as in the COMPLOT experiment, with several preliminary simplifications and gradually increased geometrical accuracy. Issues like the non-conservation of the mass flow and related oscillations in the calculated pressure and force fields are addressed. At first, the displacement is imposed, according to SCK•CEN theoretical calculations. Then it should be inferred by Newton’s law from the force balance on the CR. In this paper, the imposed displacement and its numerical handling are illustrated. The numerical methodology and results will in the future be validated against the COMPLOT experimental tests and will be used further to support the MYRRHA design.

@InProceedings{PMK15a,
  author       = {Profir, M. and Moreau, V. and Kennedy, G.},
  title        = {NUMERICAL ANALYSIS OF MYRRHA CONTROL ROD SYSTEM DYNAMICS},
  booktitle    = {16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16)},
  year         = {2015},
  keywords     = {MYRRHA, liquid lead, safety rod systems, dynamic mesh},
  url          = {https://publications.crs4.it/pubdocs/2015/PMK15a},
}