Analysis Of Physical Characteristic For An Accelerator-driven Subcritical Molten Salt Transmutation Reactor

Accelerator-driven subcritical molten salt reactor?ADS-MSR?has many unique advantages and features for advanced nuclear fuel utilization.Benefitting from the subcritical characteristics,the safety of ADS is higher than traditional critical reactors.The higher safety performance allows for a higher MA loading,making the accelerator-driven subcritical system be very flexible for spent fuel incinerating.Compared to traditional solid fuel reactors,the application of molten salt fuel enables a relatively easy online fuel processing,subsequently achieving significantly high neutron economics and fuel utilization.Basing on the existing research achievements of ADS and molten salt reactor,this study aims to analyze the neutronics performance of ADS-MSR.The impacts of molten salt fuel,on-line reprocessing,on-line refueling,subcriticality and Minor Actinides?MA?loading on the Th-U breeding and MA transmutation capability were analyzed.Finally,a conceptual design for the accelerator-driven subcritical molten salt transmutation reactor?ADS-MSTR?was developed.Based on the neutron transport program MCNP5,the burnup program ORIGEN–2 and the coupling program MOCBurnup,a fuel processing sequence which can be used for the on-line reprocessing and refueling in an accelerator driven subcritical molten salt reactor was developed.In order to study the influence of molten salt fuel in ADS,the spallation neutron yield,the neutron spectrum and the Th-U breeding capability in an accelerator driven subcritical molten salt reactor were analyzed.Results show that the effective neutron yield of molten salt fuel target is more than 50%lower than that of traditional heavy metal spallation target,limited by the mole ratio of heavy metal nuclides in molten salt fuel.Heavy metal materials were selected for spallation target in this work.In the reactor core,the fuel salt enhances the moderation to spallation neutrons and fission neutrons and the moderating effect reduces the Th-U breeding capability at the beginning of burnup,the CR of FLi,FLiBe and oxide fuel were 1.023,1.062 and1.068 respectively.On the other side,with on-line refueling and fuel processing,the CR of FLi and FLiBe salt become higher than oxide fuel in the first year and 3rd year of the burnup,and can stabilize around 1.06 and 1.00 for a long period of time,respectively.In order to analyze the Th-U breeding and MA transmutation capability of an accelerator-driven subcritical molten salt reactor,a primary design of Th-U fuel cycle ADS-MSR simulation model based on MSFR was developed.Breeding capacities including conversion ratio and net ²³³U production for various subcriticality and different minor actinides?MA?loadings are analyzed for an ADS-MSR.The results show that subcriticality of the core has a considerable impact on the Th-U breeding.A high subcriticality is favorable to improve the conversion ratio,increase the net ²³³U production and reduce the doubling time.Specifically,the doubling time for k_effff of0.99 is larger than 80 years while the counterpart for k_effff of 0.93 is only about 22 years.On the other side,in an ADS-MSR with a high initial MA loading,MA leads to the nonnegligible ²³³U depletion in the first two decades while increases the net ²³³U production compared to the reactor without MA loading.During the 50 years of operation,for the subcritical reactor(k_eff=0.97)with MA fraction increasing from 1%to 14%,the net ²³³U production rises from 3.94 t to 8.24 t.A concept design of accelerator-driven subcritical molten salt transmutation reactor?ADS-MSTR?was developed in terms of nuclear fuel selection,core structure design,carrier salt selection,fuel HN composition and fuel management,etc.The whole operation cycle can be divided into three stages:start-up phase,equilibrium phase and shut-down phase,according to feeding mode,reactivity control and fuel composition.The design of the ADS-MSTR ultimately achieved the following objectives:?1?Shut-down refuelling is no longer necessary throughout the reactor designed life?2?Excellent MA transmutation capability during the operation of reactor?3?Minimize MA discharge mass at the end of the reactor life.During the start-up and the equilibrium phase,the mass of TRU burned is basically equal to the feeding mass of MA and Pu during this period.The transmutation mass ratio of MA and Pu is about 9:1.The average annual incineration mass of MA is about 335.81 kg.During shut-down phase,the reactor will burn more Pu and the average annual transmutation mass of MA will drop to 207.88 kg,due to the gradual decline of HN mole share and MA/Pu mass ratio in fuel salt.The mass of residual MA in the core decreased from 3302.68 kg to 974.42 kg,which greatly reduced the difficulty of residual MA reprocessing.