A new methodology for enhanced natural safety GEN-IV SFR core design: application to a carbide-fueled core

In France, Sodium cooled Fast Reactor (SFR) is the leading candidate for a GEN IV prototype, to be operated as early as 2020. Compared to earlier reactor generations (Phenix, Super-Phenix), GEN IV SFR requires attractive economics while meeting safety and non-proliferation criteria. Mixed oxide fuels (U,Pu)O2 are considered as the reference fuels for the core of the SFR prototype due to their important and satisfactory feedback experience. However carbide fuels are considered as innovative fuels for a prospective SFR fleet since carbide-fueled SFRs can offer a different type of optimization which might overpass oxide fuel technology. The METRO methodology (Mathematical Estimation of Transients for Reactor design Orientation) is developed with the objective of taking into account accidental transient performance at an early stage of the core-design process. Loss-of-flow, loss-of-heat-sink and over-power transients are taken into account. A carbide-fueled SFR of 1500 MW(e) called CAR4, described in this paper, is designed with this METRO methodology. The METEOR fuel thermomechanics code is used to assess the irradiated carbide fuel behavior in nominal conditions. Because of the large carbide fuel swelling leading to pellet cladding mechanical interaction, the core-averaged fuel burnup is unlikely to significantly exceed 100 GWd/MT for an optimized Na-bonded pin design with relevant cladding (avoiding risks of failure). (authors)