Research On Key Technologies Of Trace-amount Airborne 14C Compounds Treatment In Nuclear Power Plant

Airborne radionuclide ¹⁴C compound is produced in any kind of nuclear power plant.¹⁴C is weakly?radioactive with 156keV and half-life period of 5730 years,which can cause long term serious radiation damage when it enters human body.Airborne ¹⁴ Ccompound produced in nuclear power plant is currently being released directly into the atmosphere.Although the annual emission amount of ¹⁴C not exceeding the national limit,it is very close to the upper limit of the standard.Some developed countries which have lots of nuclear power plants,such as Canada,America,have carried out a certain research on the treatment technique of airborne¹⁴C compound.However,most of their research is focused on the sampling device.The research on trace-amount airborne ¹⁴C treatment devices,which is compact,modularized,and efficient to meet the requirement of nuclear power plant,is still major difficult task to be resolved.Comprehensively considering of the technical feasibility,capital investment,amount of waste generated and the factor of small-scale,the treatment technique of trace-amount CH₄catalytic oxidation and trace-amount CO₂ absorption are chosen to be studied in this paper.As for trace-amount CO₂ absorption and fixation technique,dry-type absorption,molecular sieve adsorption and wet-type absorption are the research directions.Source analysis in waste gas emission system?TEG?in typical nuclear power plant of pressured water reactor is conducted,result of which is taken as the design input of this paper,in order to ensure the research is practically applicable.In the research of catalytic oxidation technique by organics e.g.CH₄,noble-metal catalysts which have good catalytic performance at low temperature are chosen to perform the research.Based on the existing study result,the formulation of catalyst is adjusted,and three kinds of noble-metal catalysts with Pt&Pd are made and tested to analyze the catalytic oxidation efficiency on trace-amount CH₄ and the influence on the catalytic reaction by different parameters such as concentration,flow speed and temperature of the tested gas.The result shows that CH₄ at ppmv level can be converted entirely with best performance in respect of stability and temperature by catalyst No.2,which takes 600-hole ceramics as carrier,modified alumina,Pt,Pd and Ce-Zr oxygen storage materials as coating.In the research of dry-type absorption technique,three kinds of single-compound absorbents of NaOH,CaO and Na₂CO₃ respectively and multi-compound absorbents of NaOH-Na₂CO₃,CaO-Na₂CO₃,an NaOH-CaO at various ratio are made to study the absorption efficiency on trace-amount CO₂ and the influence on absorption efficiency by different parameters such as humidity and linear speed.The result shows that10%NaOH-90%CaO multi-compound absorbent has the best performance among all the absorbents.The adsorption and desorption treatment on the CO₂ which is not chemically reacted after dry-type adsorption can further increase the absorption efficiency.13X,5A,and activated carbon from coconut shell are chosen to conduct the research of adsorption ability and desorption ability.The experiment result shows that the adsorption ability of 13X molecular sieve is obviously higher than 5A molecular sieve and activated carbon molecular sieve.Therefore,13X is chosen to be the adsorbent used in this research.In the research of wet-type absorption technique,two-step method of NaOH+Ca?OH?₂chemical absorption is determined after the comprehensive consideration of the technical feasibility,capital investment and amount of waste generated.The absorption method of multi-stage absorption tower with bubble absorption and multi-stage spray is finally used after experimental research.Based on the research of the above-mentioned key techniques,trace-amount¹⁴Ctreatment experimental device is finally developed and corresponding experiment is also conducted.The result shows that CH₄ at ppmv level can be oxidized 100%through the catalytic oxidation module and the absorption efficiency of dry-type absorption and wet-type absorption is both higher than 95%.The absorption efficiency of the whole experiment device is higher than 95%...