Innovative core design for generation IV sodium-cooled fast reactors

The design of innovative cores for Generation IV Sodium-cooled Fast Reactors (SFRs) must chiefly focus on an improving safety performance levels and competitiveness, with the aim of achieving all fundamental goals set for Generation IV systems. In this context, one priority is to create a core design such that, in the event of a serious accident, all risks of generalised fuel meltdown are avoided. The core must therefore be optimised to reduce the sodium void reactivity effect whilst acting as a self-converter with respect to the fuel itself. Design options are compared by using the physical sensitivity and parametric studies that were carried out, in order to highlight the most attractive approach for meeting the goals. A very large number of combinations of theses design options are possible. For a high power European Fast Reactor core (1500 MWe) with Oxide fuel (UO2-PuO2), the goals can be met, with the sodium void effects nearly halved, to a value of around 3 to 4 dollars, by selecting options, such as: -) a tight grid assembly design, -) introduction of a sodium plenum in the assembly's upper section, and -) introduction of a moderator material. The use of a denser fuel such as Carbide is shown to be very attractive. Its higher density means that a near-zero Internal Breeding Gain can be achieved. Most importantly, its thermal conductivity, which is significantly higher than that of the oxide fuel allows for optimisation options. Either the overall core volume can be reduced by increasing linear power density, or the margin between fuel operating temperature and melting point can be increased. (authors)