Actinide Analysis from Large-Volume Seawater Samples

Bill Burnett & Guebuem KimDepartment of Oceanography

Florida State Universityand

Phil HorwitzPG Research Foundation

Acknowledgments

Pavel Povinic, Jerry LaRosaIAEA Marine Environment Laboratory,

Monaco

PG Research Foundation

3

Marine Environment LaboratoryMonaco

Need for Large Volumes

Activities of fallout Pu in the open sea very low — on order of 0.01 mBq/kg!

To obtain good precision with reasonable count times (~1 week) requires volumes on the order of 100-400 liters!

How can we preconcentrate/separate actinides efficiently from such a large volume?

MnO2 Co-precipitation

• Seawater, 100-400 liters• Acidify to pH 2, add Pu/Am tracers, stir/hold• For 100L sample, add 35 mL sat KMnO4 (~2.1g);

Pu-->Pu(VI), org oxid, purple color• Adjust pH to 8-9 with NaOH• Add 0.5M MnCl2 (2x vol of KMnO4); --> MnO2 ppt,

dark brown

2MnO4- + 3Mn2+ + 2H2O = 5MnO2 + 4H+

•Re-adjust pH to 8-9 as necessary•Stir occasionally to keep MnO2 suspended for few hours•Allow Mn02(Pu, Am) ppt to settle overnight•Pump supernatant into clean tank for Cs, Sr processing•Drain MnO2 slurry from bottom tap

Seawater

MnO2

Suspension

MnO2 ppt(Pu, Am)~4400 mg!

supernatantCs, Sr

centrifuge/filter

Transferring Water and MnO2

Supernatant seawater transferred from one plastic tank to another via pumping — this will be used for 90Sr and 137Cs.

MnO2 suspension withdrawn from bottom of conical-shaped plastic tanks — processed for Am and Pu.

Fe(OH)3 ppt• Dissolve MnO2 w (~2L) 2M HCl + (~20-40 mL)

NH2OH.HCl (0.1g/mL)• Add 50 mg Fe3+ as FeCl3 --> yellow• Add (~1.5L) 2M NaOH to decrease acid conc.• Add ~2mL NH2OH.HCl to reduce Fe3+ --> Fe2+

Pu*-->Pu3+; colorless soln• Add 20 mL NaNO2 (0.1g/mL); Fe2+ --> Fe3+;

Pu3+ --> Pu4+

• Add 2M NH4OH to pH = 8-9; ppt Fe(OH)3

• Boil ~5 min to improve coagulation of Fe(OH)3 ppt

• Adjust pH to 6-7 w 1M HCl to hold Mn in soln• Let cool, settle, centifuge Fe(OH)3 suspension,

filter supernatant, dissolve ppt in acid for separation

MnO2 ppt(Pu, Am)

Mn2+ soln(Pu, Am)

Mn2+, Fe2+ soln(Pu3+, Am3+)

Fe(OH)3 ppt(Pu, Am)

Chemical separations

Collection of Fe(OH)3 ppt

Fe(OH)3 is ppt and allowed to settle in 10-liter glass beakers

Supernatant from Fe(OH)3 suspension filtered through a 0.45 m filter

2-Column Separation: Part 1

Load 2.5M HNO3 - 0.5M Al(NO3)3Fe(II) sulfamate, ascorbic acid

Rinse 2.5M HNO3Fe(II) sulfamate

1

2

U/TEVA

TRU

1

1

2

2

•Resin®

•Resin®

[Discard or to Sr•Resin]

1 2

U, Th, Np

Am, Pu

Actinide Separation: Part 2

U/TEVA

•Resin®

1

23

1 2

Np, Th

U

3

1

2

9M HCl

3

5N HCl - 0.05 H2C2O4

0.01M HCl

2.5M HNO32.5M HNO3 - 0.1M NaNO22.5M HNO3

1

2 9M HCl

3

4

4M HCl

0.1M NH4HC2O4or

4M HCL + 0.1M H2Q

TRU

1

1

2

2

•Resin®

4

3

Discard

Am

Pu3

4

Results: Irish Sea Water

ParameterIAEA

RecommendedValue*

mBq/kg

IAEAConfidence

Interval*

mBq/kg

MEL/FSUResult

mBq/kg

MEL/FSUYield

%

239,240Pu 13.2 12.4-14.0 14.1±0.8 99.0

238Pu 3.16 2.80-3.82 3.0±0.2 99.0

241Am 16.0 8.40-20.0 17.0±1.1 95.0

*IAEA Intercomparison (Povinic, pers. comm.)

Am Spectrum

Pu Spectrum

Summary & Future Plans

MnO2/Fe(OH)3 ppt effectively concentrates actinides from large volumes.

UTEVA/TRU effectively and easily separates Pu/Am from Fe(OH)3 matrix.

Investigate use of Diphonix for actinide preconcentration from large volumes.