This paper present the core optimization of the 1000 MW (electric) French commercial Sodium Fast Reactor, aimed at selecting few optimal configurations with respect to both core safety and reactor cost criteria. The Generation-IV reactor core design process must conciliate multiple goals (e.g. highest reactor safety levels in any situation, easy exploitability, affordable cost), which are sometimes opposed. The optimization of the core design is usually realized on the basis of expert advices and local parametric studies, which require a strong knowledge of physical phenomena. However there is no guarantee to obtain the most reliable design since the parametric space is not fully explored.
To overcome this limitation EDF has developed for more than 10 years a method for global multi-objective optimization of SFR cores: the SHADOC-based Design Development System (SDDS). The SDDS methodology relies on a multi-physics tool, including neutronics (ERANOS code), thermal-mechanics (GERMINAL code) and thermal-hydraulics (in house code) modelling. It ensures an exhaustive scan of the available design options within a given range of variation of the main reactor parameters (e.g. pin/cladding size, height and volume of the core, fertile plate height and position, etc.) by exploiting surrogate models built on a reduced number of multi-physics evaluations.
With the objective of reducing the reactor cost of the future French commercial Sodium Fast Reactor (SFR), a CEA/FRAMATOME/EDF Working Group was commissioned to work on the first specifications to be retained for a 1000 MW (electrical) commercial SFR. Reduction of the vessel and the core diameters were identified among the possible options to improve the competitiveness of SFRs. Thus, in the last two years, several studies have been carried out by EDF, leading to the definition of optimized cores by means of the SDDS multi-objective optimization tool.
Amongst all the core designs exhibiting a favorable behavior in both CRW (Control Rod Withdrawal Accident) and ULOSSP (Unprotected Loss of Station Service Power) unprotected transients, two compact low-Sodium Void Reactivity Effect cores were selected for their reduced fissile core diameters :
- The first one is based on a 12-fuel subassembly rows design, which perfectly meets the core size criteria (arbitrarily set to a fissile core diameter lower than 4 m),
- The second one, based on a 13-fuel subassembly rows design, although slightly wider, exhibits a better behavior for the two unprotected accidents considered (ULOSSP and CRW).
Their characteristics and performances will be detailed in the paper.
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