Preliminary Physical Design And Optimization Of Burnup For Small Natural Circulation Lead Cooled Fast Reactor(SNCLFR-100)

SNCLFR-100(Small Natural Circulation Lead Cooled Fast Reactor with 100MWth),proposed by University of Science and Technology of China(USTC)based on practical technology,is a typical modular fast reactor with an array of heterogeneous square fuel assemblies using MOX as the main fuel located in the core,and a preliminary conceptual design has been presented.For the reactor,the economics of its operation has a great relationship with its one through fuel cycle.In general,extending one through fuel cycle of the core could improve the reactor's economic effects.Firstly,in this paper,we calculated the physical parameters of the existing SNCLFR-100 core design scheme,including the power distribution of the core and the neutron flux distribution and other steady-state parameters,and reactivity coefficients and other transient parameters,as well as the prompt neutron lifetime and delayed neutron fraction and other dynamic parameters.The scheme meet design criteria and constraints.And we got the result that the core could run for 4 years without refueling in this design scheme.Based on this calculation result,this paper proposes a physical design optimization goal that extending the one through running time of SNCLFR-100 from 4 years to over 10 years.Secondly,this paper presents a series of design criteria and constraint constraints that need to be followed in optimization.As the thermodynamic hydraulic design has been coupled,we have determined that,give priority to other parameters to optimize the physical design without changing the size of the core structure as far as possible.And we took reducing the core neutron loss and increasing the core residual reactivity as the two directions for optimal design.The full power operating time of the core was extended to over 10 years without refueling through optimizations,including changing compositions of the fuel,adjusting the relative portion of Pu and U,and changing the type of structure material in the core.Finally,after the optimization scheme was determined,the fine modeling of the core was reestablished,and the physical parameters were recalculated.Compared to the original design,the neutron flux distribution became flatter,and the power peak factor of the core dropped from 1.40 to 1.37.And at the same time,from the result of negative reactivity coefficient,its neutronics,relevant design parameters accord with safety design requirements,which proved that the optimization was feasible.And the one through fuel cycle of this design was over ten years.The SNCLFR-100 core physical design optimization work in this paper could provide a reference for further optimization analysis or reactor design optimization under similar conditions.