uranium isotopic ratio determinations in uranium - … · uranium isotopic ratio determinations in...

Uranium Isotopic Ratio Determinations in Uranium Salts and

Pitchblende

David Urban

Investigation Objectives • Characterise uranium contained in samples in

terms of isotopic abundance and ratios

• Focusing on the isotopes 234U, 235U, 238U are the results from the method sufficiently accurate and reproducible?

• Is it possible to differentiate between samples?

• How can we use this information?

• Opportunity to assess the effectiveness of different digestion methods for pitchblende

2

Analysis - Digestion • 6 uranium salt samples and 1 sample of

pitchblende

• Uranium salt samples digested using conc. HNO3

• Pitchblende sample digested using a range of procedures

1. Conc. HNO3

2. 1:3 mixture of conc. HNO3 and HCl respectively

3. Temperature controlled microwave digestion using a 2:1 mixture of conc. HNO3 and HCl respectively

4. Temperature controlled microwave digestion using 1.5 mL concentrated HF, 5 mL of concentrated HCl and 8 mL of HNO3

3

Analysis - Calculations

• Final source to be analysed by AS contained approximately 0.3 Bq of uranium activity - Measurable activity with good resolution and acceptable

uncertainty

- Mass of salt to be digested for desired activity calculated based on an assumption of 100% activity due to 238U – specific activity conversion

4

Analysis - Sample Purification • After digestion sample purification by extraction

chromatography • Digestion residues dissolved in 3 M HNO3-1 M

Al(NO3)3 and passed through columns containing UTEVA® resin

• Sequential rinses to elute possible impurities - 3 M HNO3 (Po removal) - 9 M HCl (resin conversion) - 5 M HCl-0.05 M oxalic acid (Th removal)

• Remaining uranium was eluted using 0.01 M HCl and collected

5

Analysis – Electrodeposition and Alpha Spectrometry

• Eluent pre-treatment - conc. HNO3 → evaporate (organic matter removal)

- 5% NaHSO4 in 9 M H2SO4 → evaporate (nitric acid removal)

- Electrolyte (NH4SO4 ) added

• Electrodeposition onto stainless steel disks - 1 Amp for 1.5 hours

• Alpha counting - Tracerless method (ratios)

- 24 hour count (low activity)

- Detection efficiency independent of alpha energies

6

Quality Control

• All samples analysed in triplicate to determine repeatability

• Pitchblende as quality control - Are the results accurate when compared to published values?

- How effective are the digestion methods in extracting the uranium from the ore? Recoveries of uranium from pitchblende determined as a ratio of the measured activity to the calculated activity in the mass of ore digested

7

0

50

100

150

200

250

300

350

400

450

3900 4000 4100 4200 4300 4400 4500 4600 4700 4800 4900 5000

Co

un

ts

Energy (keV)

Alpha Spectrum for a Uranium in Pitcheblende

238U

235U

235U

234U

235U α-energy region of interest Probability 10.9%

238U

235U

235U

234U

238U

235U

235U

234U

235U α-energy region of interest Probability 74.8%

Results – uncertainty minimisation • Tailing of 234U

peak interfering with 235U region of interest (ROI)

• Positive bias to 235U activity

• Solution: discard ROI for 235U between 4445 KeV and 4645 KeV in activity determination - easier than applying tailing correction

8

Sample ID mass/mass isotopic percentage

234U 235U 238U

uranyl acetate 1 0.002501 0.509 99.489

Uncertainty (k=2) 0.000099 0.018 0.018

uranyl acetate 2 0.002253 0.492 99.506

Uncertainty (k=2) 0.000041 0.054 0.054

uranyl nitrate 1 0.002441 0.470 99.527

Uncertainty (k=2) 0.000040 0.031 0.031

uranyl nitrate 2 0.000653 0.2576 99.7418

Uncertainty (k=2) 0.000017 0.0078 0.0078

uranyl nitrate 3 0.002280 0.501 99.4969

Uncertainty (k=2) 0.000060 0.026 0.0257

uranium oxide 0.0020528 0.505 99.493

Uncertainty (k=2) 0.0000077 0.067 0.067

0.527% U3O8 Pitchblende 0.00523 0.740 99.255

Uncertainty (k=2) 0.00012 0.036 0.036

Results – Mass percentages • Good overall

reproducibility • Uncertainties

- highest for 235U (some greater than 10%) and;

- low for 234U - lowest for 238U

• Reasons - 235U activity lowest and small

relative mass percentage - 238U activity high with very

large relative mass percentage - 234U activity high with very

small relative mass percentage

• Translated to lower uncertainties in 234U/238U ratio than 235U/238U

9

Results – Comparisons with Pitchblende • All isotopic mass

percentages were in agreement with published values

• Statistical analysis

showed no significant difference between the literature and experimental results

10

Condition Probability Status

u < 1.64 Greater than 0.1 The reported result does not differ significantly from the expected value

1.95 > u < 1.64 Between 0.1 and 0.05

The reported result probably does not differ significantly from the expected value

2.58 > u < 1.95 Between 0.05 and 0.01

It is not clear whether the reported result does not differ significantly from the expected value

3.29 > u < 2.58 Between 0.01 and 0.001

The reported result is probably significantly different from the expected value

u > 3.29 Less than 0.001 The reported result is significantly different from the expected value

Definition of u-test Conditions (Shakhashiro, IAEA, 2005)

Uranium Isotopic Mass Percentages in Pitchblende Sample

234U 235U 238U

Published data (Firestone, 1999) 0.0055 0.7200 99.2745

Uncertainty (k=2) 0.0005 0.0012 0.0060

Experimental results 0.00523 0.740 99.255

Uncertainty (k=2) 0.00012 0.036 0.036

u-test 1.03 1.13 1.10

0.00E+00

1.00E-05

2.00E-05

3.00E-05

4.00E-05

5.00E-05

6.00E-05

7.00E-05

23

4U

/23

8U

Uranium Isotope Ratios (234U/238U)

uranyl acetate 2

uranyl nitrate 1

uranyl nitrate 2

uranyl acetate 1

uranyl nitrate 3

uranium oxide

0.527% U3o8 pitchblende

Published Natural

Results – 234U/238U • Experimental

uncertainties very low

• Results for pitchblende agree with published values and fall well within the published uncertainties

• Differentiation is certain between some salt samples

• Differentiation is probable in between some salt samples

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u-test comparison between uranium salts for 234U/238U

uranyl acetate 1 uranyl acetate 2 uranyl nitrate 1 uranyl nitrate 2 uranyl nitrate 3 uranium oxide

uranyl acetate 2 2.32

uranyl nitrate 1 0.57 3.23

uranyl nitrate 2 18.49 35.35 40.91

uranyl nitrate 3 1.77 0.60 1.98 26.20

uranium oxide 4.72 5.13 9.95 4.30 4.30

pitchblende 35.30 46.97 44.23 75.53 43.80 53.26

Results – 234U/238U Statistical Analysis • Two uranium salt

samples could be differentiated from the salts analysed (u≥3.29)

• There was a probable difference between two salts (3.29˂u˃ 2.58)

• The pitchblende sample could be distinguished from all of the salt samples (u≥3.29)

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1.95 > u < 1.64 Between 0.1 and 0.05 The reported result probably does not differ significantly from the expected value

2.58 > u < 1.95 Between 0.05 and 0.01


3.29 > u < 2.58 Between 0.01 and 0.001 The reported result is probably significantly different from the expected value



0.00E+00

1.00E-03

2.00E-03

3.00E-03

4.00E-03

5.00E-03

6.00E-03

7.00E-03

8.00E-03

9.00E-03

23

4U

/23

8U

Uranium Isotope Ratios (235U/238U)

uranyl acetate 2

uranyl nitrate 1

uranyl nitrate 2

uranyl acetate 1

uranyl nitrate 3

uranium oxide

0.527% U3o8 pitchblende

Published natural

Results – 235U/238U • Experimental

uncertainties much higher

• Results for pitchblende agree with published values BUT in this case the published value falls within the larger experimental uncertainty

• Differentiation is possible with only one salt sample

13

u-test comparison between uranium salts for 235U/238U

uranyl acetate 1 uranyl acetate 2 uranyl nitrate 1 uranyl nitrate 2 uranyl nitrate 3 uranium oxide

uranyl acetate 2 0.30

uranyl nitrate 1 1.06 0.34

uranyl nitrate 2 12.61 4.31 6.61

uranyl nitrate 3 0.32 0.11 0.69 8.95

uranium oxide 0.40 0.41 0.77 4.00 0.40

pitchblende 11.51 7.70 11.36 26.21 10.96 5.62

Results – 235U/238U Statistical Analysis • Only one

uranium salt sample could be differentiated from the salts analysed (u≥3.29)

• The pitchblende sample could be distinguished from all of the salt samples (u≥3.29)

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1.95 > u < 1.64 Between 0.1 and 0.05 The reported result probably does not differ significantly from the expected value

2.58 > u < 1.95 Between 0.05 and 0.01


3.29 > u < 2.58 Between 0.01 and 0.001 The reported result is probably significantly different from the expected value



Results - Digestions

• Acid Digestions - High yields

- Low uncertainties

• Microwave Digestions - Total extraction of

uranium from ore

- Lower uncertainties

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0.527% U3O8 Pitchblende Digestion Yields (% mass/mass)

Digestion Method 1 Mean 94.3

HNO3 Uncertainty (k=2) 3.1


HNO3 and HCl Uncertainty (k=2) 5.2


Microwave HNO3 and HCl Uncertainty (k=2) 1.3


Microwave HF, HNO3 and HCl Uncertainty (k=2) 2.8

Conclusions • The experimental results were both accurate and

repeatable/reproducible • 234U/238U was better than 235U/238U for differentiating

between salt samples • Discrimination was reliant on there being sufficient

difference between the ratios • All the digestion procedures used were effective in

extracting high yields of uranium from the pitchblende ore

• Temperature controlled microwave digestion resulted in total extraction of the uranium in the ore

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CONTACT ARPANSA

Email: [email protected] Website: www.arpansa.gov.au Telephone: +61 3 9433 2211 Freecall 1800 022 333 General Fax: +61 3 9432 1835 A technical report supporting this presentation can be found on the ARPANSA Website http://www.arpansa.gov.au/Publications/technicalreports/index.cfm

THANK YOU

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