Lessons learned on pool-systems simulation by CFD tools

In the framework of several European projects, CRS4 has given a large contribution and has gained an important expertise in the modeling and numerical support of various experimental facilities developed for the LMFRs design. The CFD models are more and more reliable and can be successfully used to support the experimental activities while being validated through the comparison with the databases generated in the experiments. The validation of the CFD modeling techniques to simulate complex 3D flow behavior in LMFRs is one of the driving purposes of the Euratom program. One aspect of major relevance in the numerical simulation is the thermal radiation modeling. In time, we became aware of its impact in the cooling of the facilities and it is important to carefully take it into account. The progressive implementation of the thermal radiations in the CFD simulations will be illustrated in the frame of the various numerical models built at CRS4 in past and present European projects. The implementation of the ray tracing for thermal radiations greatly increases the requirement of computational resource. Moreover, the confidence toward the possibility to include it in the GEN IV HLM context was acquired only recently. For these reasons, different equivalent techniques have initially been employed. Successively, the thermal radiation model embedded in the CFD software was implemented in the numerical models, wherever relevant. The overwhelming relevance of radiation modeling came out during the SESAME project, in which lead solidification and re-melting experiments and CFD modeling in a pool were performed. The modeling was quite sensitive to physical parameters like the external thermal conditions and the vessel wall emissivity. It was found out that radiation losses were responsible for half the total heat losses and this aspect should not be neglected at all. Details about the modeling of the thermal radiation will be given. In the MYRTHE project, in the CFD modeling of the CIRCE-HERO facility, the radiative heat flux from the LBE free surface through the cover gas was taken into account by setting a heat sink at the LBE/gas interface. At that moment, the thermal conditions at the top of the facility were not really known and at best educated guesses were used. In the ongoing PATRICIA project, for the CFD modeling of the CIRCE-THETIS facility, the radiative heat fluxes from the gas insulation of the various internal components are modeled by means of an increased thermal conductivity. The thermal radiation model is implemented in the cover gas and in the reactor vessel air cooling system (RVACS). The treatment of the thermal boundary conditions of the computational model which includes the vessel insulation layer is still currently under examination and its progress status will be presented.

@Misc{PM22c,
  author       = {Profir, M. and Moreau, V.},
  title        = {Lessons learned on pool-systems simulation by CFD tools },
  month        = {november},
  year         = {2022},
  keywords     = {CFD simulation, LMFR, LBE, CIRCE },
  url          = {https://publications.crs4.it/pubdocs/2022/PM22c},
}