61st Radiobioassay & Radiochemical Measurements Conference, Iowa City, IA
|Dr. Tabatadze presenting at the RRMC meeting in Iowa City.|
The USTUR's George Tabatadze and Elizabeth Thomas attended the 61st Annual Radiobioassay and Radiochemical Measurements Conference (RRMC) in Iowa City, IA, October 25 - 30. The USTUR laboratory recently analyzed a MAPEP soil sample to validate the Registries' tissue analysis protocol for high-fired plutonium oxide. Dr. Tabatadze presented the results of this effort at the meeting.
Analysis of High-Fired Plutonium Oxide and Other Actinides in MAPEP Soil Samples
George Tabatadze (USTUR), Elizabeth M. Thomas (USTUR), Sergei Y. Tolmachev (USTUR)
Recently, the Radiological and Environmental Sciences Laboratory (RESL) presented results of the Mixed Analyte Performance Evaluation Program (MAPEP) for actinides in soil. In this laboratory evaluation test, substantial number of participants failed on 239Pu analysis. It has been concluded that incomplete sample digestion and analyte dissolution was a primary cause of failure. The United States Transuranium and Uranium Registries (USTUR) performed a study to verify USTUR standard procedures used for actinide analysis in human tissues. MAPEP-11-MaS24 soil was received by the USTUR. This reference soil was certified for 239Pu, 241Am, 234U, and 238U concentrations and plutonium was presented in the form of 'high-fired' 239PuO2. Samples of 0.5, 1.0, and 2.0 g were collected in triplicate and were microwave digested at a control temperature of 200 ºC and monitored pressure of 40 bar for 20 minutes using concentrated HNO3-HCl-HF or HNO3-HCl reagent mixture. After a sample was spiked with tracers, actinide (Pu/U/Am) separation was carried out on TEVA-TRU-DGA extraction chromatographic column consisting of 1-ml cartridges. Following electrodeposition, activities of Pu, U, and Am fractions were measured by α-spectrometry. Regardless of sample size, complete soil digestion was achieved with HNO3-HCl-HF, while HNO3-HCl yielded insoluble residue. The average chemical tracer recoveries were 34.3±6.2%, 100.8±1.7%, and 98.3±4.9% for 243Am, 242Pu, and 232U, respectively. Low 243Am recovery was attributed to the soil matrix effect. Measured average concentrations of 239Pu, 241Am, 234U, and 238U in samples digested with HNO3-HCl-HF were 2.54±0.16, 1.64±0.12, 4.41±0.09, and 4.61±0.11 pCi g-1, respectively. These values were not statistically different from certified 239Pu, 241Am, 234U, and 238U concentrations with negative bias of the mean of 4.0%, 1.3%, 7.2%, and 7.0%, respectively. Using HNO3-HCl, only 5% (0.14±0.01 pCi g-1) of the initial 239Pu was dissolved and recovered from the solution. The remaining residue was digested with HNO3-HCl-HF and 239Pu concentration was calculated to be 2.42±0.10 pCi g-1 resulting in a combined value of 2.56±0.10 pCi g-1 (bias -3.4%). Negative bias of 77.6%, 72.1%, and 71.9% for 241Am, 234U, and 238U, respectively, was also observed with HNO3-HCl. Incomplete dissolution of the analyte using HNO3-HCl results in a low actinide recovery from the sample, while HNO3-HCl-HF allows for complete dissolution of all actinides present in soil, including high-fired plutonium oxide.
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