| On the premise of meeting the power output and safe operation of nuclear power plant,in order to reduce the unit electricity cost of nuclear power plants,a reasonable fuel management scheme needs to be established.In 2011,Shanghai Institute of Applied Physics of Chinese Academy of Sciences leads the TMSR project which aims at developing Molten Salt Reactors(MSRs),mainly studying liquid molten salt reactor(LMSR)with graphite moderation and fluorine salt cooled pebble bed high temperature reactor(PB-FHR)with spherical components.The fuel of liquid molten salt reactor is dissolved in molten salt in the form of liquid state,the nuclide concentration of fuel salt is uniformly mixed in the primary circuit,and the fuel is continuously reprocessed on-line;The fuel pebbles of fluorine salt cooled pebble bed high temperature reactor have double heterogeneity,move continuously in the core and pass through the core many times until reaching the discharging burnup.These characteristics bring new challenges to fuel management calculation.Therefore,the research on fuel management of molten salt reactor has important academic significance and pratical value for MSR design and optimization.Firstly,according to the properties of uniform fuel mixing and continuous reprocessing,a fuel management analysis code LMSR is developed and verified,and homogenization,continuous post-processing and fuel feeding search are studied.Specifically,it includes: 1)Suitable homogenization method is developed based on the geometry characteristics of LF1.Integral reactivity value of different control rod groups,power distribution of the core and the temperature reactivity coefficient are calculated by applying 7 few group constants.2)The homogenization and burnup of liquid molten salt reactor with hexagonal module are calculated.Evolution of effective multiplication factor with burnup is calculated by using equivalent energy spectrum.3)The conditions of continuous removal of fission gas and continuous addition of fuel in molten salt reactor are calculated and validated by modifying the burn up module of the original DRAGON.4)In order to conserve the molar mass fraction of heavy metals in the core and maintain the effective multiplication factor between(1.0,1.005),the feeding search module of liquid molten salt was developed,which can search the mass of Th-232 and U-233 in batch post-processing or continuous post-processing mode.Based on the code LMSR,the neutronics performance of 150 MWth small modular molten salt reactor(SMMSR)was calculated.3)the utilization of thorium increased rapidly to 43% in the first two periods,then decreased slowly to 38%,and finally reached 45% from the fifth cycle;4)the temperature reactivity coefficient was negative in the whole 60 years of life,and the negative value was large when the reactor was started,and then gradually increased and stabilized at about-3pcm / K.Secondly,according to the properties of fuel balls moving continuously and passing through the core many times in the pebble bed fluoride salt cooled high temperature reactor(PB-FHR),a fuel management analysis code PBMSR is developed and verified,and homogenization and fuel ball movement are studied.Specifically,it includes: 1)In order to solve the problem of leakage effect in homogenization process and calculate the molten salt group constant of lower chamber,the three-step homogenization process is applied.2)Based on the PBMSR,the burnup performance of PB-FHR without refuelling is calculated and verified.3)The continuous moving model of the fuel pebble in different flow channels and the management model of fuel pebble is established.Considering that the fuel management mode of high temperature gas reactor(HTGR)is similar to the PB-FHR,PBFHR is used to calculate the burnup and axial power distribution of HTGR under one pass and multiple pass fuel management mode.The results show that the PBMSR is in good agreement with literature,which verifies the correctness of pb-msr.Based on the code PBMSR,the fuel management scheme of 1GWth PB-FHR was calculated.Considering that the deepest burnup of the discharged core depends on the parameters of a single fuel ball,the optimization of a single fuel ball is carried out first.The optimization parameters are divided into two categories,geometric parameters and material parameters.The geometric parameters include: 1)the diameter of the fuel ball,including four diameters of 3,4,5 and 6cm;2)the volume filling ratio of triso in the fuel ball;3)the geometric form of the kernel in triso,including the uniform mixing of Th-232 and U-233,Th-232 in the inner layer,and U-233 in the inner layer.The material parameters are the mole enrichment of U-233 in heavy metals.The results show that: 1)according to the requirement that the buoyancy of the fuel ball is greater than the gravity,the triso volume filling ratio is less than 13%;2)according to the requirement that the temperature reactivity coefficient is negative,the U-233 molar concentration is 14%-20%;3)according to the performance of the burnup,the U-233 molar concentration is 14% and the Th-232 and U-233 uniformly mixed kernel structure is selected;4)according to the capability of the fuel ball burnup detection device,a 6cm diameter fuel ball is selected 5)considering the uniformity of the axial power distribution,the fuel management scheme that the fuel ball circulates in the core 31 times and then discharged from core is selected.Finally,in order to calculate the economic performance of molten salt reactor,the theoretical model and cost unit price are studied,an economic analysis code MSR-ECONS for molten salt reactor is established and verified.The theoretical model includes: 1)adding the calculation model of small modular reactor;2)developing the corresponding calculation model of fuel cost according to the fuel cycle mode of liquid molten salt reactor.The cost unit price includes: 1)according to the special fuel cycle front end and back end of liquid molten salt reactor,the more accurate cost unit price is given through investigation and analysis.In order to verify the correctness of msr-econs,it is compared with G4-ECONS,which is an economic analysis program developed by the fourth-generation reactor forum.The results show that the two programs are in good agreement,thus verifying the correctness of msr-econs.Based on the code MSR-ECONS,the unit electricity cost of the nuclear power system of 150 MWth SMMSR and 1GWth PB-FHR is analyzed.The results show that: 1)the unit electricity cost of SMMSR is $48.44/MWh;2)the unit electricity cost of PB-FHR is $53.12/mwh.The higher cost of the more mature PWR($47.97 / MWh)is due to the higher cost of fuel U-233 used in both operations.However,SMMSR can effectively reduce the demand of U-233 in the front channel of fuel cycle through fuel reprocessing,so the unit electricity cost is lower than that of PB-FHR.In short,research on the fuel management methods are performed for LMSR and PBMSR,and the codes of LMSR and PBMSR are developed and verified.In order to calculate the unit electricity cost of the above two types of reactor,the economic analysis code MSR-ECONS was developed and verified.On this basis,the corresponding analysis is carried out for 150 mwth SMMSR and 1gwth PB-FHR.The conclusions that obtained provide reference for molten salt reactor,and the LMSR,PBMSR,MSR-ECONS codes can be also used for the fuel management optimization of MSR. |
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