A semi-passive approach to GFR depressurized decay heat removal accidents

With the advent of the U.S. lead Gen IV initiative to develop an entirely new generation of nuclear reactor plants, there is now the opportunity to revisit the design of the gas-cooled fast reactor (GFR) and enhance the safety case. The GFR safety approach for the passive removal of decay heat in a protected depressurization accident with total loss of electric power needs to be different from that taken for the HTRs. The HTR conduction cooldown to the vessel wall boundary mode for economically attractive core is not feasible in the case of the GFR because the high power densities require decay heat fluxes well beyond those achievable by heat conduction and radiation heat transfer mode. A set of alternative novel design options has been evaluated for potential passive safety mechanisms unique to the GFR. What has been selected for further development under the auspices of the France-US INERI collaboration is the natural convection option with a block/plate type derated core and a combination approach balanced between passive and active means. A guard containment will still be utilized but it will be sized for an LWR containment range of backup pressure.