Thermal-hydraulic analyzes of a slow loss of flow accident in the IEA-R1 Nuclear Reactor using RELAP and CFD codes

Abstract

Among the most critical accidents for the IEA-R1, there is the Loss of Flow Accident (LOFA) in which a sudden and abrupt stop of the primary pump causes the loss of flow. Traditionally, this kind of accident is analyzed by thermal-hydraulic system codes. However, they can overestimate the fluid and fuel temperature along the transient by up to 20%. Moreover, thermal-hydraulic system codes can face difficulties to capture three-dimension phenomenon, such as the natural convection. Meanwhile, Computational Fluid Dynamics (CFD) analysis has shown good results when analyzing open-pool research reactor accidents even dealing with flow inversion. This work presents a thermal-hydraulic analysis of a Slow Loss of Flow Accident (SLOFA) in the IEA-R1 using the RELAP5 code and the commercial CFD code Ansys CFX®. The objective is to combine the advantages of both approaches. The system code was used to find the transient boundary conditions for a CFD model. The CFD software solved the detailed flow pattern in a quarter of a fuel channel. The numerical results showed good agreement with the benchmark data. The peak temperatures were overestimated in only 1.8 °C in the fluid and 3 °C in the cladding.