Simulation And Study Of Fracture In Nuclear Graphite Used In Molten Salt Reactor

After the study of more than fifty years,in 2000,the molten salt reactor is assigned as one of the candidate reactors in the fourth generation reactor international forum.In 2011,Chinese academy of sciences launched “Advanced Fission Energy Program” within the framework of the Strategic Priority Research Program.Thorium molten salt reactor nuclear energy system(TMSR)as one part of this program,is committed to research and development in the fourth generation advanced nuclear energy system.Nuclear graphite with its high temperature resistance,irradiation resistance,stable chemical properties and small neutrons absorption,is an important structural material for the nuclear reactors.In molten salt reactor,nuclear graphite is used as the moderator,reflector and structural material as well.So the integrity of the nuclear graphite component will affect the actual service life of the reactor.Therefore the fracture analysis of nuclear graphite is necessary.In this thesis,based on the finite element analysis,two numerical studies of nuclear graphite have been carried out.The first study is about the tensile strength of nuclear graphite.The tensile strength is important in nuclear graphite assessment,it is because the tensile strength is the smallest in all the material strengths of graphite.The Brazilian disc test is a common method to measure the tensile strength of brittle materials.However the original Brazilian disc test can't be applied to graphite.In order to make the Brazilian disc test can be applied to the nuclear graphite,several new anvil designs for the test have been developed in this thesis.All the new designs have been analysed by the finite element method.The numerical results showed that an anvil with an arc and an extended section adjacent the arc is the most effective design for the nuclear graphite.The second study is about the effect of keyway root radius on graphite structures.The keyway is a common structure in the graphite component.It is important to understand the effect of keyway root radius on failure stress of graphite structures.In this section,a series of four-point bending test has been performed.The failure stresses of graphite samples with different chamfering radius have been measured.In order to find a fracture model which can predict crack initiation and crack propagation in graphite,several different failure models have been analysed and compared with experimental results.The extended finite element method has been used in the analyses.The predicted failure stresses from the numerical results are within 5% of experimental results.So the extended finite element method can be used to simulate the crack propagation of nuclear graphite,which lays a foundation of simulation of the experiments that are more complicated or difficult to implement in the future.