Abstract:"Thorium-based Molten-Salt Reactor(TMSR) nuclear energy system" is one of the "Strategic Priority Research Program" of CAS.With the mission to research and develop fission energy system of the fourth generation,the TMSR project intends to construct 2MW Thorium-based molten-salt reactors,form up R&D capability concerning techniques that support the evolution of TMSR nuclear energy system by 2020,then solve major technological challenges in Th-U fuel cycle as well as Thorium-based molten-salt reactor,build pilot TMSR of industrial scale,and achieve effective utilization of Thorium resource as well as composite utilization of nuclear energy.Th-based fuel has several advantages: a high transfer ratio of 232Th/233U,able to breed in thermal reactor,a less production of highly toxic radioactive nuclides,and a good non-proliferation.However,challenges still remain in fuel fabrication,strong gamma radiation from daughter nuclide of 232U which brings trouble in re-processing and re-fabrication,intermediate nuclide 233Pa in Th-U transfer chain absorb neutron in the core.Nuclear fuel can be used in open cycle,modified opencycle,and closed cycle.Being one of the six candidate Gen-IV reactors,MSR is very suitable for Th-U fuel.MSR combined with online dry reprocessing method is quite promising to achieve fully closed cycle of Th-U fuel.Proposed in the beginning of this century,FHRs use fluoride salt as coolant and TRISO fuel.Pebble-bed FHR can achieve modified open cycle of Th-U fuel.The feature of high temperature output makes MSR one of the major candidates for non-electricity application of nuclear energy.The high temperature output can be used directly in exploitation of shale oil,hydrogen production etc.