Some thermal hydraulic challenges in sodium cooled fast reactors

Sodium cooled fast reactors have been developed in France for nearly 50 years with successively Rapsodie, Phenix and Superphenix plants. Thermal hydraulic challenges have progressively increased with the power and the size of the reactors. After Superphenix stop in 1997, the thermal hydraulic activity on sodium cooled fast reactors was drastically reduced for about 10 years. Nowadays, the so-called Astrid prototype developed in France in the frame of Generation IV deployment requires thermal hydraulic inputs to support the design and safety studies. This paper aims at summarizing the main thermal hydraulic challenges in sodium cooled fast reactors, on the basis of the past experience. Numerical and experimental tools used in the French Atomic Energy Commission (CEA) are briefly presented. The improvement on numerical simulation is emphasized with some examples of recent computations. Of course, this review is not a comprehensive one as it is mainly based on the author experience. The items covered in this paper are the subassembly, the core, the upper plenum, the lower plenum, the decay heat removal, the gas entrainment and the piping. Heat exchanger thermal hydraulics is also briefly mentioned. Several experimental and computed results are presented as simple illustrations without quantitative information on the data.