[en] An external neutron source is required to provide additional neutrons for a proper operation of a sub-critical system. Spallation neutron sources, though very effective in neutron production, are large, expensive and presently would involve certain difficulties in their operation (e.g. beam trips). In this paper we investigate the use of an external neutron source driven by an electron accelerator. The lower performance of the neutron source (compared to spallation based neutrons) could be balanced by a surrounding multiplier core, operating in a slight under-critical regime with k_eff ∼ 0.995 like in the case of a so-called Beta Compensated Reactor. An electron driver is rather cheap and compact machine that might bring many advantages in terms of reliability. An overall comparison between the electron-neutron converter and spallation process is done including a schematic layout for an electron driver coupled to a sub-critical core with some preliminary calculations of the nuclear system parameters (k-effective, neutron fluxes, reactor power, etc...). (authors)

[en] An external neutron source is required to provide additional neutrons for a proper operation of a subcritical system. Spallation neutron sources, though very effective in neutron production, are large, expensive and presently would involve certain difficulties in their operation (e.g. beam trips). In this paper we investigate the use of an external neutron source driven by an electron accelerator. The lower performance of the neutron source (compared to spallation based neutrons) could be balanced by a surrounding multiplier core, operating in a slightly under-critical regime with k_eff ∼ 0.995 like in the case of a so-called Beta Compensated Reactor. An electron driver is rather cheap and compact machine that might bring many advantages in terms of reliability. An overall comparison between the electron-neutron converter and spallation process is done including a schematic layout for an electron driver coupled to nearly critical core with some preliminary calculations of the nuclear system parameters (k-effective, neutron fluxes, reactor power, etc.). (author)

[en] One of the key research goals for Generation IV Sodium-cooled Fast Reactors (SFR) is to improve their safety levels, particularly by ensuring robust core behaviour during accident conditions. A dedicated approach called COCONS has been developed to reach these objectives. This paper discusses this approach which focuses on the design of naturally safe core. It can be broken down into three stages: The first stage involves defining the role of feedback reactivity coefficients applicable during accident transients, such as unprotected reactivity insertion transients (UTOP) or unprotected loss-of-cooling-flow transients (ULOF). The parametric study has revealed the impact of the Doppler effect on UTOP and sodium temperature coefficient which is directly related to the sodium void effect for ULOF. The second stage is to define optimised ranges for these reactivity coefficients to avoid any core damage by fuel meltdown or sodium boiling. Conclusions differ greatly depending on the fuel type, e.g. oxide, metal or carbide. Fuel temperature margins before fuel meltdown and average fuel temperatures play a very important role. The third stage involves recommending several core concepts that are capable of achieving these idealistic ranges. Several new oxide fuel subassembly designs are suggested in view of reducing the maximum fuel temperature and increasing margins to fuel meltdown. Ceramic carbide fuel seems to be a very promising choice from a reactor physics viewpoint. Combined with moderator material in the core or used with the new fuel 'plate' subassembly concept, ceramic carbide fuel seems capable of achieving safe natural behaviour during either a UTOP or ULOF transient. The COCONS approach appears to be a useful tool in terms of recommending new SFR core options and comparing overall performance levels with reactor safety levels. Final optimization will require more general comparisons, taking into account all the main Generation IV goals i.e. economic competitiveness, minimised waste production, resource savings, reduced proliferation risks, and enhanced safety. (author)