Abstract: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, concentrated nitric acid, and hydrofluoric acid. It was then heated to dryness and dissolved in 9M hydrochloric acid. After treatment, ₆₃^{Ni and ₅₅}Fe were separated and purified using sodium hydroxide precipitation, anion exchange chromatography, and nickel specific resin extraction. The measurement was then performed using liquid scintillation method. The measurement results show that the final stable recovery rates of Ni and Fe are 98.8% and 95.8%, respectively. The minimum detection limit and minimum detectable activity for ₆₃^{Ni are 208 (counting) and 0.041} Bq, respectively. The minimum detection limit and minimum detectable activity for ₅₅^{Fe are 208 (counting) and 0.144} Bq, respectively. The actual activity concentrations of ₆₃^{Ni and} ₅₅^{Fe in the samples are 76.9} Bq/g and 30.4 Bq/g, respectively. The recovery rate simulation experiment was conducted using standard soil substances, achieving a recovery rate 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 can effectively coprecipitate Ni and Fe and remove most of Re, Sr, and all Cs at pH between 8.7 and 11.1; The decontamination factors for Co, Fe, and Zn in the nickel fraction of anion exchange chromatography are all above 660, while the decontamination factors for Co, Eu, Mn, Ni, Sr, Zn, and Zr in the iron fraction are all above 2000. This work also studied the purification effects of DMG precipitation method and nickel specific resin method on Ni, respectively. The recovery rate of Ni by DMG precipitation method was 87.14%, and the recovery rate 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 method and ion exchange resin method should be used for preliminary separation.The method established in this work is simple to operate, has a high recovery rate, and can meet the needs of monitoring ₆₃^{Ni and} ₅₅^{Fe in retired nuclear facilities.}