Influence Of Acidity On Extraction Of Zirconium And Ruthenium In PUREX Process Co-decontamination Unit

With the development of nuclear energy,the disposal of spent fuel has been paid more attention.At present,China is preparing to build large-scale spent fuel reprocessing plants.The Purex process is the only widely used spent fuel reprocessing process in the world,but countries have improved it according to their own circumstances.The COEX process of our country is mainly improved according to the process of Ager plant.Mainly to prevent nuclear proliferation and not to produce pure plutonium products.For this process,1AF use 4.5mol/L nitric acid in feed,and 1AS use 2mol/L nitric acid in scrubbing.However,zirconium can be easily extracted in the extraction section under these conditions.In the washing section,the acidity is low and it is easily extracted into the aqueous phase,which may cause the zirconium to circulate in the 1A process.In this paper,for the co-decontamination process of Purex process,the main process of spent fuel reprocessing plant,the influence of acidity change on the extraction of zirconium and ruthenium was studied.The main conclusions are as follows:(1)The effect of acidity on the decontamination of zirconium and ruthenium under the condition of uranium free and high saturated uranium was investigated by batch experiment.The results show that under the condition of uranium free and high saturated uranium the increase of acidity is disadvantageous to the decontamination of zirconium,but the increase of acidity is conducive to ruthenium decontamination.However,the extraction efficiency of zirconium and ruthenium by TBP is greatly reduced under the condition of high saturated uranium,and the change under the influence of acidity is much smaller than that under the condition of no uranium.(2)A multi-stage extraction bench test was carried out in mixer-settler.The effect of 1AF feed acid and 1AS washing acid on the extraction of zirconium and ruthenium was investigated.The results show that the increase of acidity of1 AF is favorable to the extraction of zirconium by TBP,and unfavorable to the separation of uranium and zirconium,resulting in poor zirconium decontamination.The increase of acidity of 1Af is not conducive to the extraction of Ru by TBP and the separation of Ru and Uranium,but the change of acidity is less than that of Zirconium.When the acidity of 1AS increases from2.5 to 3mol/L,not conducive to TBP extraction of zirconium and ruthenium,but it can enhance the washing of water relative to zirconium and ruthenium in washing section and is helpful to remove zirconium and ruthenium in organic phase.(3)After the end of the bench test operation,samples of each stage in the mixed clarifying tank were sampled and analyzed.The results show that the increase of 1AF acidity will increase the accumulation of zirconium in aqueous phase in mixer-settler,especially at levels 6-8.The change of 1AS washing acid has little effect on the accumulation of zirconium.A small amount of ruthenium was also accumulated in the aqueous phase of the extraction section in mixer-settler.Acids also accumulate in the aqueous phase of the extraction section in mixer-settler.Uranium did not accumulate in the aqueous phase in the extraction stage,because TBP extracted uranium thoroughly,leaving little residue in the aqueous phase.