液体闪烁法测量退役混合土中^(63)Ni和^(55)Fe

Liquid Scintillation Method for Measuring ^(63)Ni and ^(55)Fe of Mixed Soil in Decommissioning Reactor

为监测退役核设施中的放射性及其排放,将经过400℃灰化4 h后的样品,用浓盐酸、浓硝酸及氢氟酸的混合酸溶解后加热至干燥,用9 mol/L盐酸溶解,处理后用氢氧化钠沉淀、阴离子交换色谱法及镍特效树脂萃取分离纯化^(63)Ni和^(55)Fe,再用液体闪烁法进行测量,建立了一种反应堆退役混合土样品中^(63)Ni和^(55)Fe的分析方法。结果表明,最终稳定Ni、Fe的回收率分别达98.8%和95.8%,对^(63)Ni的最小探测限和最小可探测活度分别为208(计数)和0.041 Bq,对^(55)Fe的最小探测限和最小可探测活度分别为208(计数)和0.144 Bq,实际样品的^(63)Ni、^(55)Fe活度浓度分别为76.9和30.4 Bq/g。采用标准土壤物质进行回收率模拟实验,达到了95%以上的回收率。分别进行了碱沉淀法、阴离子交换色谱法从多种元素中分离Ni、Fe的实验,其中氢氧化钠沉淀法在pH值处于8.7~11.1时便可以有效使Ni、Fe共沉淀,并去除大部分Re、Sr和全部Cs;阴离子交换色谱法洗脱的镍组分中对Co、Fe、Zn的去污因子均在660以上,铁组分中对Co、Eu、Mn、Ni、Sr、Zn、Zr的去污因子均达2000以上。还分别考察了DMG沉淀法和镍特效树脂法对Ni的纯化效果,DMG沉淀法的Ni回收率为87.14%,镍特效树脂法在镍-干扰元素比例达10∶1以上时,Ni的回收率即接近100%,且干扰元素如Ba、Eu、Fe、Mn、Sr的去污效果达到最佳,因此在使用镍树脂前,宜采用其他方法(如碱沉淀法、离子交换树脂法)进行初步分离。建立的方法操作简单,回收率高,能够满足监测退役核设施中^(63)Ni和^(55)Fe的需求。

To monitor radioactivity and its emissions in retired nuclear facilities,this study established an analytical method for^(63)Ni and^(55)Fe in mixed soil samples from a decommissioning reactor.After ashing at 400℃for 4 hours,the sample was dissolved in a mixture of concentrated hydrochloric acid,nitric acid,and hydrofluoric acid,and then heated to dryness and dissolved in 9 mol/L hydrochloric acid.Subsequently,^(63)Ni and^(55)Fe were separated and purified using sodium hydroxide precipitation,anion exchange chromatography,and nickel specific resin extraction,and then measured by the liquid scintillation method.The results showed that the final stable recovery rates of Ni and Fe were 98.8%and 95.8%,respectively.The minimum detection limit and minimum detectable activity for^(63)Ni and^(55)Fe were 208(counting)and 0.041 Bq,208(counting)and 0.144 Bq,respectively.The actual activity concentrations of^(63)Ni and^(55)Fe in the samples were 76.9 Bq/g and 30.4 Bq/g,respectively.The recovery simulation experiment was conducted using standard soil substances,achieving a recovery of over 95%.Experiments were conducted on the separation of Ni and Fe from various elements using alkali precipitation and anion exchange chromatography,respectively.Among them,the sodium hydroxide precipitation method effectively coprecipitated Ni and Fe,and removed most of Re,Sr,and all Cs at pH value between 8.7 and 11.1.The decontamination factors for Co,Fe,and Zn in the nickel fraction of anion exchange chromatography were all above 660,while the decontamination factors for Co,Eu,Mn,Ni,Sr,Zn,and Zr in the iron fraction were all above 2000.This work also investigated the purification effects of DMG precipitation method and nickel specific resin method on Ni,respectively.The recovery of Ni by DMG precipitation method was 87.14%,and the recovery of Ni by nickel resin method was close to 100%when the nickel interference element ratio was above 10∶1.Moreover,the purification effect of interference elements such as Ba,Eu,Fe,Mn,and Sr was the best.Therefore,before using nickel resin,other methods such as alkali precipitation and ion exchange resin should be used for preliminary separation.This method is simple to operate and has a high recovery,which can meet the needs of monitoring^(63)Ni and^(55)Fe in retired nuclear facilities.