Sodium fast reactors offer the most promising type of reactors to achieve such Generation IV goals at a reasonable time scale given the experience accumulated over the years. However, it is recognised that new regulations and safety rules as they exist worldwide are requiring improved safety performance. In particular, one of the foremost Generation IV International Forum (GIF) objectives is to design cores that can passively avoid core damage when the control rods fail to scram in response to postulated accident initiators (e.g. inadvertent reactivity insertion or loss of coolant flow). The analysis of such unprotected transients depends primarily on the physical properties of the fuel and the reactivity feedback coefficients of the core. Under the auspices of the Working Party on Scientific Issues of Reactor Systems (WPRS), an Expert Group Task Force was formed to investigate Sodium Fast Reactor core Feed-back and Transient response (SFRFT) in order to identify recent progress in this field. The work was focused on a shared analysis of the feedback and transient behaviour of the next generation SFR concepts.
In order to achieve these goals, it was decided to start with a series of benchmarks on which the different participants could compare their abilities to calculate the nominal performance characteristics and the global safety parameters. The work concentrated on two different core sizes: two large size cores (3600 MW thermal) and two medium size cores (1000 MW thermal) and three types of fuel: oxide, carbide and metal. The “expert group” provided initial core descriptions for both size cores  in September 2011. The comparative study concentrated on the following items:
The present report summarises the results obtained by the Working Party on Scientific Issues of Reactor Systems (WPRS) for the benchmark exercise.