Lab Exercise - Determination of Plutonium and Americium from Sediment Sample

Developed By

Laboratory of Radiochemistry
Department of Chemistry
University of Helsinki
Finland

Learning Goals

Here the learning goals and purpose of the exercise should be presented in a reasonable way.

Explanation and Exercise Guide

Theory

^239,240Pu, ²³⁸Pu and ²⁴¹Am in the environment originate mainly from atmospheric nuclear weapons tests in the 1950-1960’s. ²⁴¹Am is a daughter nuclide of ²⁴¹Pu, and its amount increases constantly in the environment due to decay of the parent.

Extraction chromatography combines efficiency and selectivity of solvent extraction and convenience of chromatographic resin. Water solution is the mobile phase and the stationary phase is organic solvent that is attached to an inert support polymer. Benefits of extraction chromatography compared to ion exchange are smaller waste amounts (acid solutions) and faster analysis.

Eichrom/Triskem's UTEVA resin is designed for separation of uranium and tetravalent actinides. TRU resin is used to separate transuranium nuclides.

Experimental Procedure

Sediment pretreatment

• 0.25 g of sediment sample is weighed into a beaker
• ²⁴³Am and ²⁴²Pu yield determinant tracers are added (2-3 dpm)
• 15 mL of concentrated HNO₃ and 5 mL of concentrated HCl is added and the mixture is gently heated on a hot plate for 2 h
• The solution is filtered through a glass fibre filter and the solution is evaporated to dryness

Separation of Pu and Am from U and Th

• The evaporation residue is dissolved in 10 mL of 3 M HNO₃ + 1.0 M Al(NO₃)₃
• 2 mL of 0.6 M ferrous sulfamate is added and the solution is stirred (reduces Pu)
• 200 mg of ascorbic acid is added under stirring (Fe stays as Fe²⁺), waiting for 10 min., filtering if any solid matter
• UTEVA column is pretreated with 5 mL of 3 M HNO₃
• The sample is loaded into the UTEVA column and the Pu and Am containing eluate is collected
• Rinse the beaker with 2x5 mL of 3 M HNO₃ and pour the rinses to the column and collect the eluate in the beaker where the eluate above was collected

Separation of Plutonium and Americium from each other

• TRU column is pretreated with 5 mL of 2 M HNO₃
• The sample collected from previous separation (UTEVA) is loaded into the TRU column
• The beaker is rinsed with 5 mL of 2 M HNO₃ and added to the column
• The column is treated with 5 mL of 2 M HNO₃ + 0.1 M NaNO₂ (Pu is oxidized)
• The column is rinsed with 5 mL of 0.5 M HNO₃
• Am is elute first with 3 mL of 9 M HCl and then with 20 mL of 4 M HCl
• The column is rinsed with 25 mL of 4 M HCl + 0.1 M HF
• Pu is eluted with 10 mL of 0.02 M TiCl₃ + 4 M HCl into Daniel tube

Co-precipitations for counting source preparations

• Am-bearing eluate is evaporated into dryness and again twice heated to dryness after addition of 3 mL of HCl + 1 mL of HNO₃ to destroy residues of resin (heat aqua regia carefully!)
• Two additional heating to dryness will be made with a few milliliters of with concentrated HNO₃. Am is then dissolved into 3 mL of 1 M HNO₃ and poured in a Daniel tube, the beaker is rinsed with 2 mL of 1 M HNO₃ and the rinses is added to the Daniel tube
• 0.5 mL of NdCl₃ solution (0.1 g/L) carrier (50 µg of Nd) is added to Pu and Am solutions
• 0.6 (Am) and 1.0 (Pu) mL of concentrated HF is added to samples
• Samples are kept in a cold place at least for 30 min
• The Pu and Am -bearing NdF₃ precipitate is filtered on 0.1µm filters in the following way:
  

1. 1. first 5 mL of water is added through the filter (to observe possible leakage of the filtering system)
   2. then 2 x 5 mL of NdCl₃ solution (0.1 g/L) is added
   3. then the sample solution is added
   4. then the precipitation tubes are rinsed with 2 x 5 mL of water and poured onto the precipitate
   5. The filters are dried at room temperature for 0.5-1 hour and glued onto a plastic disc.
   6. The filters are measured for their Pu and Am activities with alpha spectrometry

Other

Reporting

• Describe in detail the whole separation procedure and explain why each step was made. Draw a separation procedure scheme.
• Calculate the chemical yields of Pu and Am separations.
• Calculate the activity concentrations of Pu and Am in the sediment and their uncertainties.

Safety Aspects

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Equipment

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Preparation for the lab Supervisor

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Feedback from Users and Supervisors

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