Preparation and Properties of Novel B4C/CF/PI/AA6061 Hybrid Composite Laminates for Spent Fuel Storage

Author:Fu Xue Long

Supervisor:tao jie


Degree Year:2018





As a clean energy,nuclear energy can effectively reduce carbon emissions,mitigate the impact of greenhouse effect and make the foundation for solving the energy problem of green and sustainable development.However,nuclear energy generates highly radioactive spent nuclear fuel(SNF)that emits alpha rays,beta rays,gamma rays,protons and secondary gamma rays,accompanying with massive amounts of heat and high-energy neutron spillage and threatening the environment and the safety of operators.With the rapid development of new nuclear reactors(Light Water Reactors--Fast Reactors--Fusion Reactors),the requirements for spent fuel storage are getting higher.Therefore,it is urgent to develop a novel spent fuel storage material with sufficient radiation resistance,to solve the problem of safe storage of spent nuclear fuel.Based on the theories mentioned above,we prepared a novel B4C/CF/PI/AA6061 hybrid composite laminates(composed of stacking layers of AA6061aluminum alloy plates,neutron shielding composite(blends of boron carbide(B4C)particles and PMR polyimide(PI)resin)and carbon fibre reinforced polyimide prepregs(CFRP))using hot molding process,and investigated its thermal stability and mechanical properties,neutron shielding performance and its mechanism,and radiation resistance systematically,to explore the potential application in the field of spent fuel storage.The main results and conclusions were summarized as follows:(1)Hot molding process of B4C/CF/PI/AA6061 hybrid composite laminates were analyzed.Anodic oxidation process of AA6061 aluminum alloy,preparation process of carbon fiber reinforced polyimide prepregs(CFRP)and B4C/PI resin neutron shielding composite were also performed.The effects of silane coupling agent on the interface between B4C particles and PI resin were emphatically discussed.The results demonstrated that the addition of silane coupling agent was conducive to improve the wettability between B4C particles and PI resin,the reason lies in that the inclusion of-Si-O-Si-and hydroxyl bonds on the surface of B4C particles enhances the interfacial adhesion between B4C particles and PI resin.The explicit curing process of novel B4C/CF/PI/AA6061 hybrid composite laminates was 80°C for 1 h,120°C for 1 h,160°C for 1 h,200°C for 1 h,280°C for 1/2h,and 320°C for 2 h.(2)The effects of various layups on the tensile,flexural and peel properties of B4C/CF/PI/AA6061 hybrid composite laminates were analyzed.Besides,the effects of experimental temperature on the tensile and interlaminar shear properties of hybrid composite laminates,as well as their thermal stability and thermal conductivity,were also investigated.Moreover,single-lap-shear(SLS)properties of neutron shielding composite(composed of B4C particles and PI resin at various weight ratios)/AA6061 aluminum alloy were tested.The testing results illustrated that the tensile strength,elastic modulus,flexural strength and flexural modulus moderately increased with the multilayer configuration ranging from 2/1 to 5/4.The delamination of flexural testing specimens aggravated,resulting in the increasing probability of fracture and delamination of outermost neutron shielding layer.Multi-layer hybrid composite laminates with 5/4 configuration exhibited the superior bearing capacity.Glass transition temperature(Tg)and effective thermal conductivity of hybrid composite laminates increased with B4C content owing to the physical cross-linking structure between B4C particles and PI resin.Tensile strength of hybrid composite laminates decreased with the increase of experimental temperature.The interlaminar shear strength hit a high point for hybrid composite laminates with 30 wt%of B4C particles,and the specimens still kept good interlaminar shear strength even at 300°C.Besides,single-lap-shear strength of the specimens firstly increased and then decreased with the increasing of B4C content,with the maximum value appeared at 30 wt%of B4C particles.If further increasing the content of B4C powder,SLS strength decreased correspondingly.(3)Thermal stability and thermal conductivity of novel B4C/CF/PI/AA6061 hybrid composite laminates with different layups were tested and analyzed.The results showed that hybrid composite laminates maintained good thermal stability with almost no loss of quality when the test temperature was lower than 300℃.But when the temperature exceeded 450℃,thermogravimetric(TG)curve presented a significant weight loss.As the testing temperature approached to 650℃,the mass of hybrid composite laminates were about 85.87%,87.75%,92.21%,93.39%and 94.43%of the initial weight,respectively.When compared with neat PI resin,glass transition temperature of hybrid composite laminates increased with B4C content.If the experimental temperature exceeds the glass transition temperature of PI resin,hybrid composite laminates will lose its support.Therefore,the usage temperature of hybrid composite laminates should be limited below 300°C or less.Thermal conductivity of hybrid composite laminates reached up to 0.55 W/(m·K).(4)Neutron shielding performance of B4C/CF/PI/AA6061 hybrid composite laminates was conducted with the combination of neutron shielding experiment and numerical simulation,and the parameters such as layup configuration and B4C content were taken into consideration.In addition,the effect of carbon fibers on the neutron shielding performance of hybrid composite laminates was further analyzed,and neutron shielding mechanism was also explored.The results indicated that neutron transmission of hybrid composite laminates decreased obviously with the increasing of the layups,owing to the increase of 10B areal density.Neutron transmission varied from 85.2%to 23.1%,when the layup configuration of hybrid composite laminates varied from 2/1 to 5/4.Moreover,carbon fibres acting as a neutron moderator had a direct effect on the neutron shielding performance of hybrid composite laminates,which can effectively increase the collision probability between neutrons and atoms,and promote the absorption of thermal neutrons.Numerical simulation results suggested that neutron transmission of hybrid composite laminates decreased exponentially with the increase of layups,which is consistent with the neutron transmission law.However,the proportion of high energy neutrons and secondaryγ-ray spectra was significantly reduced,and secondaryγ-ray energy was concentrated on 0.5 MeV.(5)The effects of different dosages of 60Co-γray irradiation on the microstructure,chemical structure,thermal stability and surface elemental distribution of B4C/CF/PI/AA6061 hybrid composite laminates were studied,and the irradiation mechanism was analyzed.Besides,the effect of low energy helium ion irradiation on the microstructure of hybrid composite laminates was also explored,as well as its radiation damage mechanism.The results illustrated that chemical stability of hybrid composite laminates remained stable even irradiated with 60Co-γray irradiation with a total dose of1000 kGy.The materials maintained good thermal stability below 400℃,while thermal stability of the specimens would be the best with the irradiation dose of 750 kGy.With the increasing ofγ-ray irradiation dose,the relative intensity of C=O bond in C1s spectra decreased gradually and the partial oxygen functional group C=O was decomposed by 60Co-γray irradiation.When the implantation dose of helium ion was 1.62×10166 ions·cm-2,the surface roughness of irradiated aluminum alloy increased,and bubbles and clusters were generated on the surface of AA6061 aluminum alloy gradually.