Numerical analysis of a dissymmetric transient in the pool-type facility E-SCAPE through coupled system thermal-hydraulic and CFD codes

Modeling and numerical simulation of transient thermal-hydraulic phenomena in pool-type systems, such as the LBE-cooled research reactor MYRRHA under development at the Belgian Nuclear Research Centre - SCK•CEN, is challenging due to the three-dimensional nature of the coolant flow field in the primary system. Phenomena such as flow mixing and thermal stratification can impact the plant dynamic response to accidental transients, and pose limitations to the application of 1D system thermal-hydraulic codes. An improvement of the current simulation techniques through the combined use of CFD and system codes is addressed in this paper, which presents a domain decomposition computational method that couples the RELAP5-3D system code with the CFD code FLUENT. Numerical stability issues, typical of domain decomposition coupling techniques, are tackled through the implementation of a novel implicit coupling algorithm based on the Quasi-Newton method. The validation of the computational method is currently carried out within the framework of the European project MYRTE (MYRRHA Research and Transmutation Endeavour), on the basis of the experimental tests planned in the facility E-SCAPE, a scaled model of the reactor primary system. The paper discusses the development of the coupled model, and presents preliminary results of a pre-test simulation of a partial loss of flow (PLOF) transient. The proof-of-principle simulation proved the validity of the coupling approach, and its capability to predict plant-scale transients involving complex tree-dimensional flow fields.