Status of new safety measures considered for European Sodium Fast Reactor in the ESFR-SMART project

Following up the previous European projects EFR and CP ESFR, a new EU project, called ESFR-SMART, was launched in September 2017. This project applies the new safety rules taking into account the Fukushima acci-dent in order to increase the safety level of the European Sodium Fast Reactor (ESFR) and reach the highest safety standards by simplifying the design and by using all the positive features of the Sodium Fast Reactors (SFR). The first ideas about the new safety measures proposed to increase the intrinsic safety level of the reactor have been presented at ICAPP 2018. This paper gives more detailed description of the new safety measures proposed for ESFR. The main measures are followings:

• Core design with improved safety parameters: special geometry and composition was designed to significantly decrease the global void reactivity effect and reduce the probabilities of severe accidents. Three types of control rods are considered, including active, i.e. human-activated, and passive, i.e. activated by physical parameters, e.g. by sodium temperature or flowrate.
• Improved primary sodium confinement: The new design of the reactor pit is proposed to be able to confine the primary sodium leaking from the reactor vessel. The level of sodium in the reactor vessel in this case is designed to remain high enough to assure natural convection through the core. A massive metallic roof above the reactor pit is assumed to assure the sodium containment even in the case of the worst severe accidents. A number of other measures are selected to avoid primary sodium leaks out of the reactor pit and the roof.
• Secondary loops design efficient in natural convection: Even in case of loss of feedwater in steam generators and loss of electricity supply for secondary pumps, the measures are taken on the secondary loops to assure an efficient decay heat removal by active or passive ways. These measures will include an optimized geometry of the secondary loops to promote the natural convection of the secondary sodium, the use of fully passive thermal pumps to increase the cooling flow rate, and the use of the steam generators modules to pro-mote the cooling of their external surfaces by the natural convection of atmospheric air.
• Special devices for the decay heat removal systems.

The main drawings of the modified ESFR, including the above-described measures, have been made and the main results are presented in the paper. Using these drawings, several calculations have begun to evaluate these measures and to demonstrate the final compliance of the proposed design to safety requirements. In the next phases of the ESFR-SMART project, the project will also recommend additional R&D needed for implementations of these safety measures in the future.