| As efficient clean energy,nuclear energy occupies an irreplaceable position in the future energy structure.To ensure the sustainable development of nuclear energy,it is necessary to reprocess spent fuel to recover useful nuclides,improve the utilization of uranium,plutonium and other resources,and ensure the reasonable disposal of radioactive waste at the same time.In the reprocessing of spent fuel,a large amount of radioactive waste liquid was inevitably produced.To avoid potential harm to human health and the environment,it is necessary to dispose of the radioactive wastewater properly.Here,evaporative concentration occupies an important position.It is mainly used to reduce the volume of radioactive wastewater,ensure the recycling of nitric acid and water,and increase the concentration of metal ions.However,during this process,there may be a risk of"red oil"explosion;meanwhile,problems such as large energy consumption,low heat conversion efficiency and severe equipment corrosion exist when using this method.Three-dimensional graphene,a kind of bulk material with a three-dimensional network structure,composed of graphene sheets as basic structural units.It has low density,large specific surface area,high porosity,good chemical stability and irradiation stability,and shows broad application prospects in the field of radioactive wastewater treatment.This thesis is mainly based on the advantages of the graphene material,through different modification treatment methods,and propose new methods to solve the deficiencies during the evaporation process."Red oil"explosion is an important safety issue in the spent fuel reprocessing and the most efficient method to prevent"red oil"explosion is to capture the organic solvent entrained in the aqueous.Here,a new method was first proposed for removing entrainment in the aqueous phase with the use of graphene materials,and to fundamentally solve the possible"red oil"explosion.First,graphene oxide?GO?precursor was synthesized using improved Hummers',and with HI as a reducing agent and PVDF as a modifier,superhydrophobic graphene/polyvinylidene fluoride composite materials were synthesized under mild conditions GA-PVDF).The preparation conditions of GA-PVDF were optimized,and the materials were characterized by SEM,FTIR,XRD,contact angle,mechanical properties and oil absorption/water absorption capacity.The results show that under optimized conditions,GA-PVDF exhibits the advantages of super-hydrophobicity?contact angle>150°?,strong water resistance,good oil-water separation and strong mechanical properties.Besides,the recyclability of GA-PVDF and adsorption performance for various organics were also studied.The results show that the material has a fast and high adsorption capacity,and at the same time,good recyclability can also reduce the generation of secondary waste.Then,taking the typical extraction equipment centrifugal extractor as an example,the phase entrainment in the post-treatment process was studied,and it was found that under certain harsh or abnormal working conditions,phase entrainment will inevitably occur.Then,the treatment of phase entrainment with GA-PVDF was studied.Batch adsorption and continuous adsorption experiments show that the proposed method can reduce the content of organic phase entrainment to less than 0.1%in a short time,it is proved that GA-PVDF has a good removal effect for phase entrainment.The proposed method may solve the possible"red oil"explosion risk from the"source".As a mature technology,evaporation is the most common method to reduce the volume of radioactive waste.However,the traditional evaporation methods have the problems of high energy consumption,low heat conversion efficiency,and serious equipment corrosion.Based on the good light-to-heat conversion performance of graphene,an efficient method for the evaporation of radioactive wastewater with solar energy was proposed here.Three-dimensional porous frozen tofu is a traditional food,which is prepared by pre-freezing and thawing fresh tofu.Inspired by this,a green and economic approach for hydrophilic modified graphene foam?MGF?synthesis using one-step reduction and air-drying was reported in this article.Using sodium ascorbate as a reducing agent and hydroxyethyl cellulose as a hydrophilic modifier,by controlling the reduction time and precursor concentration,MGF with a little or without volume shrinkage can be obtained after a simple pre-freezing,thawing and air-drying step of the graphene hydrogel.Subsequently,an interface evaporation system using sunlight as a heat source,MGF as a light-to-heat conversion material,and polystyrene foam as a heat-insulating layer was proposed for the evaporation treatment of radioactive waste liquid.The effects of acidity,salinity and radiation intensity on the evaporation performance were studied.The results showed that MGF has good water evaporation performance.Using this interfacial evaporation method,the evaporation efficiency of water is 91.9%under 1sun,and the evaporation rate reaches 1.42 kg·m-2·h-1,which is5 times of pure water(0.28 kg·m-2·h-1)under the same condition.Using this system,the evaporation experiment of simulated radioactive waste liquid was also carried out under natural sunlight.The results show that the method has good purification performance for radioactive wastewater.This evaporation method has the advantages of simple and the temperature of bulk water low.In practical applications,it can effectively solve the problems of high energy consumption and equipment corrosion compared with the traditional evaporation method,and it opens up a new way for the low-cost and efficient treatment of radioactive wastewater. |
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