| The surface radioactive contamination generated in the process of nuclear energy development and nuclear decommissioning is harmful to the environment,human body and other living things.The decontamination of surface radioactive contamination is one of the key problems to be solved in the development and utilization of nuclear energy and the decommissioning of nuclear facilities.The strippable membrane decontamination method is an effective decontamination technology for surface radioactive pollution.However,most of the existing decontamination materials and technologies are used at room temperature,which can not be used in the decontamination of surface radioactive pollution in low temperature areas.In view of the requirements of decontamination of radioactive contamination on the surface,nuclear emergency and protection in low temperature region,the resources abundant and renewable biomass of hydroxypropyl methyl cellulose,bayberry tannin,and polyethylene acetate with good film-forming performance and a large number of active functional groups are used as raw material,two kinds of low temperature detergents with sprayable,film-forming,strippable property and efficient decontamination are prepared through grafting and composite modification technology.The effects of the mass fraction of polyethylene acetate,hydroxypropyl methyl cellulose grafted vinyl acetate copolymer,Bayberry tannin,sodium dodecyl sulfonate,glutamic acid and citric acid,solvent type and concentration,environmental temperature and humidity,pollution time and surface roughness of contaminated materials on the low-temperature spray,fluidity,film-forming and peelability of two detergents were studied.The effects of decontaminant composition and decontamination process conditions on the film formation time and decontamination characteristics of simulated radioactive U(VI)contamination on ceramic,glass,polyethylene,stainless steel and other contaminated plates were also studied at low temperature.The composition of detergent and process conditions were optimized.The synthesis,modification and decontamination mechanism of detergent were analyzed by modern testing technologies such as infrared spectrum,X-ray energy spectrum,scanning electron microscope and thermal analysis.The main research contents and results are as follows:(1)With the increase of the mass fraction of polyethylene acetate,bayberry tannin and sodium dodecyl sulfonate,the decontamination rate of polyethylene acetate based detergents increased to a certain extent,and the film-forming time decreased.With the rise of the relative humidity,the decontamination rate goes up,and the film-forming time also increases gradually.With the rise of the ambient temperature from-10℃ to 0℃,the decontamination rate of the detergents increases,while the film-forming time decreases gradually.The pollution time has no obvious effect on the decontamination rate.The influence of different kinds of pollution board on the decontamination rate of detergents has a great relationship with the roughness of pollution board.The surface roughness of ceramic,glass and stainless steel is relatively small and the decontamination rate is high.However,the surface roughness of polyethylene plastic board is relatively high,and its decontamination rate is low.The maximum decontamination rates on the surfaces of glass,ceramic,plastic and stainless steel are 96.89%,97.12%,90.07% and 95.23% respectively at optimal conditions.There are some pores on the surface of the decontamination membrane which are helpful for the adsorption and decontamination of uranyl ions by the decontamination agent.The decontamination mechanism of polyethylene acetate based decontamination agent is the result of the physical action of adsorption and adhesion of decontamination agent to uranium pollution,and the joint action of the complexation of hydroxyl,carbonyl and sulfonic groups in decontamination agent to radionuclide uranium.(2)The grafting yield was high when the ratio of hydroxypropyl methyl cellulose to vinyl acetate was 2:3 and the grafting time was 6h.Hydroxypropyl methyl cellulose grafted vinyl acetate copolymer formed uniform and transparent sol in ethanol/water(9:1)solvent.When the temperature was more than-20℃,the sol fluidity was fine.The mass concentration of the graft copolymer increased in the range of 5%~40%,and the viscosity of the sol increased from 194.5mPa.S to 384.9mPa.S at the temperature of-5℃.When the mass concentration of the hydroxypropyl methyl cellulose grafted copolymer sol is in the range of 20%~30%,the spray property,film forming and film stripped performance of the graft copolymer sol are all good.The tensile strength of the graft copolymer membrane increased from 6.02 N before modification to 45.5N after modification.(3)The decontamination rate of the detergent increased and the film forming time decreased with the increase of the mass concentration of hydroxypropyl methyl cellulose graft copolymer,the mass fraction of bayberry tannin,sodium dodecyl sulfonate,glutamic acid,citric acid,and the volume fraction of ethanol in the solvent of ethanol/water.In the range of-10℃~-2℃,the decontamination rate increased slightly with the increase of ambient temperature,and the film formation time decreased.With the increase of the relative humidity of the environment in the range of 30% to 80%,the decontamination rate of the detergent increased slightly and the film formation time also increased gradually.The pollution time had little effect on the decontamination rate of the detergent.The surface roughness of glass,stainless steel and ceramic was lower than that of plastic plate.The decontamination rate of detergent on the surface of glass,stainless steel,ceramic plate and plastic plate reached 97.89%,94.56%,92.02% and 90.02% respectively.The film formation time of detergent was within 12 hours.The optimal composition of the detergent was: 20% of mass concentration of hydroxypropyl methyl cellulose graft copolymer,5% of the mass fraction of bayberry tannin,4% of the mass fraction of sodium dodecyl sulfonate,and 5% of the mass fraction of glutamate,and 90% of the volume fraction of ethanol solvent.The maximum peaks of weight loss rate appeared at 350℃ and 308℃.The total weight loss rates of combustion in a nitrogen atmosphere were 81.2% and 70.01%,respectively.In addition to physical adhesion,the decontamination mechanism of hydroxypropyl methyl cellulose graft copolymer detergents for U(VI)pollution also included hydroxyl complexation,carbonyl complexation,sulfonic acid complexation,carboxyl complexation and other complexation,and ion exchange of sodium dodecyl sulfonate. |
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