CFD SIMULATION OF NATURAL CONVECTION COOLING AFTER A LOSS-OF-FLOW TRANSIENT

摘要

Natural convection cooling is of ever-increasing importance in nuclear reactor safety, particularly for long transients. One relevant accident scenario is the Protected Loss-of-Flow (PLOF) transient, which relies on natural convection cooling for decay heat removal in many pool-type and integral-vessel reactors. A reference design investigated here is the Prototype Gen-Ⅳ Sodium Fast Reactor (PGSFR), a pool-type design with 150 MWe output power. Whole-vessel steady-state Computational Fluid Dynamics (CFD) simulations of a reference PGSFR design were performed in STAR-CCM+ to assess the long-term cooling capability of the Decay Heat Removal Heat Exchangers (DHXs) for a PLOF scenario. A porous media approach was employed for a number of internal structures to make the problem tenable. It was found that a segregated flow method with an additional dissipation term for pressure yielded results comparable to those of the recommended coupled flow solver, but with greater solver robustness and faster convergence. CFD results were compared with 1-D SAS4A/SASSYS-1 system code simulations, which showed reasonable agreement. These simulations provide evidence that placement of the DHXs in the cold pool is appropriate, and that effective long-term cooling of the core decay heat could be feasibly achieved for the PLOF transient.