A new CFD modeling method for flow blockage accident investigations

• Porous-jump treatment is applied to CFD simulation on flow blockages.
• Porous-jump treatment predicts consistent results with direct CFD treatment.
• Relap5 predicts abnormal flow rate profiles in MTR SFA blockage scenario.
• Relap5 fails to simulate annular heat flux in blockage case of annular assembly.
• Porous-jump treatment provides reasonable and generalized CFD results.

Inlet flow blockages in both flat and annular plate-type fuel assemblies are simulated by (Computational Fluid Dynamics) CFD and system analysis methods, with blockage ratio ranging from 60 to 90%. For all the blockage scenarios, mass flow rate of the blocked channel drops dramatically as blockage ratio increases, while mass flow rates of non-blocked channels are almost steady. As a result of over-simplifications, the system code fails to capture details of mass flow rate profiles of non-blocked channels and power redistribution of fuel plates. In order to acquire generalized CFD results, a new blockage modeling method is developed by using the porous-jump condition. For comparisons, direct CFD simulations are conducted toward postulated blockages. For the porous-jump treatment, conservative flow and heat transfer conditions are predicted for the blocked channel, while consistent predictions are obtained for non-blocked channels. Besides, flow fields in the blocked channel, asymmetric power redistributions of fuel plates, and complex heat transfer phenomena in annular fuel assembly are obtained and discussed. The present study indicates that the porous-jump condition is a reasonable blockage modeling method, which predicts generalized CFD results for flow blockages.