Preliminary safety comparison of lead-cooled fast reactors with advanced fuels in unprotected transients

The lead-cooled fast reactor (LFR) is an important component of Generation-IV reactors, with many advantages and flexible applications. The evaluation and improvement of safety features have received special attention, especially when it comes to the application of new fuel types. The paper investigates the safety performance of LFRs with MOX, carbide, nitride, and metallic fuel in unprotected transient UTOP, ULOF and ULOHS. The core neutronics model is based on Monte-Carlo code OpenMC, by which the elementary reactivity feedback coefficients are calculated. The safety analysis model of the reactor primary circuit without scram transient is based on the one-dimensional point kinetic system code ASYST. The OpenMC-ASYST results are verified by the benchmark results of the ALFRED safety analysis. By learning from the state-of-the-art LFR designs with different advanced fuels, the core designs with MOX, carbide, nitride, and metallic fuel are separately proposed. The outcomes show that nitride and carbide fuel feature a higher potential safety margin over MOX fuel under unprotected transient scenarios. The safety potentials of metallic fuel vary in different transients. A sensitive analysis is applied to key parameters of different transients. The model and simulation results in this paper provide a reference for further design and research of lead-cooled fast reactors.