Research On M~2LFR-1000 Transient Thermal Safety Characteristics Based On Multi-Scale Coupling Methodology

The lead-cooled fast reactor has good neutronic,thermal-hydraulic characteristics and inherent safety,and is a fourth-generation reactor with great development potential.Since most of lead-cooled fast reactors feature a pool-type primary cooling system,there are some complicated coolant flow field and three-dimensional phenomena in the reactor,such as local flow mixing and thermal stratification.These phenomena can affect the evolution of safety-relevant parameters;and in turn,these local three-dimensional phenomena are directly dependent on the boundary conditions determined by the system scale.The traditional best-estimate system thermal-hydraulic code uses the one-dimensional model,which cannot accurately simulate the three-dimensional phenomena in the pool-type reactors.Due to computer limitations,the CFD program is temporarily unable to perform simulations at the entire reactor system level.To overcome these difficulties,the 1D-3D coupled thermal-hydraulic code ATHLET-OpenFOAM was developed.Based on this coupled code,this paper uses the medium-modular lead-cooled fast reactor M2LFR-1000 as the research object,and carries out the multi-scale transient thermal-hydraulic safety research on the primary coolant system of the pool-type lead-cooled fast reactor.(1)The design scheme of M2LFR-1000 was briefly introduced,including the overall system of the reactor and the important core components design.And the coupled code ATHLET-OpenFOAM for multi-scale transient thermal safety research was briefly introduced,which laid a foundation for the study of multi-scale transient thermal-hydraulic safety characteristics of lead-cooled fast reactor.(2)The coupled code ATHLET-OpenFOAM was then validated,including a simple lead open loop,a simple lead closed loop and a complex closed loop.The verification results showed that the coupling parameters in the coupled code were well and fully converged,and revealed the capability of the coupling method to predict better the dynamic response of transients influenced by local three-dimensional phenomena,which can be used for the multi-scale transient thermal safety characteristics of the M2LFR-1000 main cooling system.(3)Based on the multi-scale coupled code ATHLET-OpenFOAM,the transient thermal safety analysis of the M2LFR-1000 primary cooling system was carried out.The variation of the main thermal parameters of the M'LFR-1000 primary cooling system and the complex three-dimensional phenomena of the hot plenum under the protected loss of flow(PLOF)and the unprotected loss of flow(ULOF)were studied in detail.The results showed that the complex three-dimensional effect of the hot plenum would have an effect on the thermal parameters of the cooling system during the accident,but M2LFR-1000 still has sufficient safety margin.This paper realizes the more accurate transient thermal safety characteristics of the primary coolant system of the pool-type lead-cooled fast reactor,and reveals the typical three-dimensional thermal phenomenon of the pool type lead-cooled fast reactor in the event of loss of flow.Related research results have further enriched the research methods of transient thermal safety characteristics of lead-cooled fast reactors,which is of great significance.