Challenges in the CFD modeling of MYRRHA Primary System

In the recent years, CFD has benefitted from the increase of computational power and the good scalability of parallel computing. In the meantime, many CFD software have greatly extended the range of physical phenomena accessible through integration with their fluid-dynamics core. This results in the opportunity to investigate in an integrated framework larger and more complex systems. In the framework of the SEARCH WP5 project, the objective is to assess the behavior of fuel redistribution under fuel pin failure conditions. In this paper we will present the challenges faced to construct the CFD modeling of the entire MYRRHA primary system. Such construction is in fact a pre-requisite to the final objective. To enforce the necessary redundancy and diversification required for nuclear safety, the CFD modeling has been developed in parallel by two institutes, VKI and CRS4, following two complementary approaches. On one-hand, VKI has investigated a single-phase steady model both with ANSYS Fluent and with OPEN-FOAM. On the other-hand, CRS4 has focused on a transient two- phase flow approach based on the Volume of fluid (VOF) method in Starccm+ to capture the upper free-surface dynamics. The two models will reunite on the final objective by using a Lagrangian particle tracking approach with one-way coupling, best suited for long term small rate release. We will look into the pro, the con and the complementarity of the solutions taken by both institute to face the challenging issues encountered. The first large issue encountered is the loss of geometrical symmetries with the evolution of the MYRRHA design versions. The second large issue has been to understand the implications of some buoyancy related thermal features of the flow, resulting in the incorporation of the structural part, thermally coupled to the fluid domain, and implications in the time scales involved. The computational power availability, while large, is still limited and compromises must be found. There are repercussions on the description of the core, the heat exchangers, the pumps, and other passive complex structures. We review and compare the solutions adopted, showing also how the physical interpretation serves to understand some criticalities. We conclude by showing how the redundancy and diversification approach has allowed a secure reaching of the SEARCH WP5 objective.

@Proceedings{MBPK14,
  editor       = {Moreau, V. and Buckingham, S. and Planquart, P. and Koloszar, L.},
  title        = {Challenges in the CFD modeling of MYRRHA Primary System},
  series       = {Proceedings of the SEARCH/MAXSIMA 2014 International Workshop},
  month        = {october},
  year         = {2014},
  address      = {Karlsruhe, Germany},
  keywords     = {SEARCH, MYRRHA, CFD},
  url          = {https://publications.crs4.it/pubdocs/2014/MBPK14},
}