Analysis Of Thorium-Uranium Fuel Breeding Base On A Spectra Zoning Molten Salt Reactor

Molten salt reactor?MSR?,as the only one of liquid fuel reactor among the six candidate reactors chosen by the Generation IV International Forum?GIF?,shows great promise of high thermal-electric conversion efficiency and inherent safety because of its running at high temperature and atmospheric pressure.Comparing to the traditional solid fuel reactor,the outstanding feature of MSR is on-line reprocessing of fission products?FPs?and refueling of fissile,which is beneficial to the decrease of neutron absorption of FPs and the saving of fissile for criticality.Furthermore,fuel breeding can be realized in both thermal and fast spectrum reactors with Th-U fuel cycle,which can make use of the abundant resource of thorium and is of low production on long-life radioactive transuranium nuclides compared to U-Pu fuel cycle.Taking into account of on-line reprocessing,a module of MSR Reprocessing Sequence?MSR-RS?was developed particularly for the burn-up simulation.It is based on SCALE6.1 and the previos work of the Th-U group.The module is verified with the benchmark of the Thorium Molten Salt Breeding Reactor?MSBR?and the Molten Salt Fast Recator?MSFR?in France from the aspects of breeding ratio?BR?,double time?DT?,and the evolution of main nuclides.The results show that the MSR-RS is suitable for the burn-up calctultion of MSR with on-line reprocessing.Then,in order to combine the advantages of high BR in fast spectrum and low fissile inventory for criticality in thermal spectrum,a single-fluid double-zone thorium-based molten salt reactor?SD-TMSR?core configuration is proposed.First,assemblies in both the inner and the outer zones are optimized by adjusting the ratios of molten salt and graphite with consideration of BR,²³³U inventory,DT,and temperature coefficient of reactivity?TCR?at the startup time.The results indicate that DT has the optimum value when the ratios of the molten salt and the graphite in the inner zone and the outer zone are 0.357 and 1.162,respectively.And the TCR can be improved to-2 pcm/K when the side length of the graphite hexagonal prism is 7.5 cm.Based on the optimized geometry,burn-up calculation with a series of on-line reprocessing rates is carried out with MSRRS.The results show that the SD-TMSR has a relatively excellent Th-U breeding performance with an initial ²³³U inventory of 1.27 t.When the reprocessing rate is 5 m3/d,only 16 years is needed for ²³³U doubling.When the reprocessing rate is 200 l/d,iso-breeding can be achieved.The results also show that TCR remains negative and inherent safety is satisfied during all the operation time.In addition,the Th-U breeding capacity of MSFR is analyzed,and the results shows that the neutron absorption of alloy is relatively large and the efficiency of fertile salt is low.So the fertile salt in the axil direction is added to improve the Th-U breeding performance and the graphite reflector is considered for fertile saving.Then based on the Improved MSFR?IMSFR?,burn-up calculation is carried out with MSR-RS.The results show that newly added axial fertile salt improves the BR obviously,while about half inventory of thorium can be saved with graphite reflector.BR above 1.10 can be achieved for more than 80 years,corresponding to the ²³³U production of 130 kg per year and DT of 36 years.Finally,the influences of 7Li enrichment on ThU breeding performance are studied for the 7Li enrichment of 99.9995% brings great challenge for the technique and economic cost.Parameters are explored including BR,²³³U production,DT,spectrum,neutron absorption,as well as the tritium production.The results show that there is no obvious decrease for Th-U fuel breeding with the 7Li enrichment of 99.95% compared to that with 99.9995%.So the 7Li enrichment of 99.95% is recommend for the molten salt fast reactor.