Measurement of Ni-59 and Ni-63 at the Savannah River Site Using Eichrom Ni

Resin

D. P. DiPrete, C. C. DiPrete, and R. A. Sigg

Westinghouse Savannah River Company

Solid Waste- Burial Grounds- E- Area Vaults

Tritium

ESH&QA- Radiological Control- Health Physics Technology

Reactors

Separations-F-Canyon-H-Canyon

High Level Waste- DWPF- H-Tank Farm- F-Tank Farm

Environmental Restoration

Analytical Development Section

Savannah River Technology Center

Analytical Development Section

The Savannah River Site

Radioactive Ni Analyses driven by Waste Characterization Needs

• Each waste receiving facility (i.e. SRS’s Saltstone, E Area Vaults, DWPF (for Yucca), NTS, WIPP,etc...) maintains unique evolving criteria. Waste packages must be characterized these criteria prior to acceptance

• SRTC required to characterize a wide variety of sample matrices– High level waste sludge and supernate – Separation Canyons waste streams – Legacy reactor programs samples – Environmental Restoration programs samples – Tritium programs samples – Miscellaneous Site radioactive waste items – Off-Site high activity waste streams (i.e. Hanford tank waste), etc...

59Ni and 63Ni Facts

• Activation products of stable Ni isotopes in reactor targets’ metal alloys – Ni-58(n,γ)Ni-59, Ni-62(n, γ)Ni-63

• Ni-63 – t 1/2 = 1.0E+02 Years

– Beta: Emax = 67 keV

• Ni-59– t 1/2 = 7.6E+04 Years

– EC: Co K1&2 6.915, 6.930 keV (29.5%), K1 7.649 keV (3.56%)

Why Are These Isotopes of Interest?

1E-10

1E-09

1E-08

1E-07

1E-06

1E-05

1E-04

1E-03

1E-02

1E-01

1E+00

10 100 1000 10000

Age of Waste

Fra

cti

on

of

Ra

dio

ac

tiv

ity

Sr-90/Y-90Cs-137Sm-151Pm-147Cm-244Pu-238Am-241Pu-241Ni-63Eu-154Pu-239Co-60Sn-121mPu-240Cm-243Am-243Ni-59Zr-93Tc-99Am-242mSe-79Sn-126U-234U-238Cm-246Np-237Cf-251U-233Cf-249Pu-242Cm-245Cs-135U-236U-235Pd-107Th-232I-129Cm-247

SRS High Activity Waste Sludge

Ni-59

Ni-63

Ni-63 Liquid Scintillation Analysis

• Ni-63 Analyses carried out by Liquid Scintillation Analysis on a Packard 2550AB, 2750AB, or a 3175AB equipped with a BGO Compton guard

• Counting windows used are 3-22keV, 22-80keV, and 3-2000keV.

• IDL’s typically ~10DPM for a 10minute count on the 2750 or 2550AB

Ni-59 X-Ray Analysis

• Ni-59 X-ray Analyses carried out using Be windowed high purity germanium semi-planar detectors and a Canberra Genie 2K based data acquisition system

• Counting efficiencies @6.9keV ~ 8.8%, FWHM 0.40keV

• Ni-59 IDL ~8 dpm(50,000 second count)

Ni-59

Ni Extractions - DMG Solvent-Solvent vs Eichrom Ni Resin

– Switched from a solvent-solvent DMG based extraction in 1997 to an SPE DMG based extraction using Eichrom Ni resin.

• Switch-over was motivated primarily by desire to eliminate mixed-waste generated by solvent-solvent method.

Initial Tests of Ni Resin

• Initial scoping protocols carried out to evaluate the decontamination factors of various isotopes using Ni columns(all done using vacuum, flow rates ~ 20ml/minute– Load solution: 5mg Ni carrier, 5ml 0.2M sodium citrate, adjusted to pH of

8-10 with ammonium hydroxide– 2 - 5ml 0.2M citrate washes followed by a 10ml rinse

– 15ml 3M HNO3 elution

• Pu, Am decontamination factors ~ 3400 • Sr/Y-90 decontamination factors ~ 1600• Co-60 decontamination factors ~ 6.4

Initial Tests of Ni Resin, Clean-up of Co-60

• Procedure adjusted in an attempt to isotopically dilute Co-60 off columns

• 5 mg Co carrier added to load solution• Decontamination factors for Co raised to

~1000, no obvious effects on Ni yields

Basic Steps of Current Ni Extraction Protocol for Aqueous Samples

• 5mg of Ni added to aliquot of sample (aliquot size dictated by customers detection limit requirements), 5mg of Co added where Co-60 is a concern

• Convert to chloride form with several ml concentrated HCl• Evaporate to dryness (hot plate, or 200ºC oven)• Re-dissolve in 20ml citrate wash solution (pH ~10.5)

– Currently using 15ml 1M Sodium Citrate, 85ml DI water, 8.5ml concentrated Ammonium Hydroxide, 2.5 ml concentrated nitric acid

• Condition column with 5 ml citrate wash• Add samples to columns, rinse with 2 5ml and a final 10ml citrate

wash

• Elute the Ni from the columns with 15ml 3M HNO3

• Convert to chloride with addition of concentrated HCl• Evaporate to dryness, re-dissolve in 1ml 1N nitric• Aliquots analyzed for Ni-59 and/or Ni-63, as well as ICP-AES for

yielding recovered Ni

• Basic approach to the Ni Column works well for matrices with low levels of interfering nuclides– Ni isotopes can be measured in the presence of

several orders of magnitude of other radioisotopes

• However, Waste Acceptance Criteria (WAC) often drive detection limits requirements for the Ni isotopes to 6 or more orders of magnitude below interfering isotopes

Challenges of Ni Analyses of High Activity Waste

Various Clean-up Resins Employed Prior to Ni Column Use

• A number of clean-up resins have been successfully used prior to Ni Extractions to remove interferences, but not Ni.– Bio-RAD AMP-1 (1 - 3N nitric range) to scrub Cs-137 from the

sample matrix

– Eichrom Actinide Resin (1 - 8N nitric) to scrub out the tetravalent and trivalent actinides, as well as the lanthanides, and Y-90

– Eichrom Sr Resin (4 - 8N nitric) to scrub out Sr-90, (Actinide Resin needed as well to scrub out Y-90

• In some situations, samples are so high in dissolved salts, they won’t form Ni-DMG– A Cation clean-up step works well, 0.001N nitric load on a 1ml

Cation bed, elute with 4N nitric

Recently Have Employed a Serial Ni Column Approach

• Followed the basic steps outlined previously up to the elution with 15ml 3M nitric, addition of 7ml concentrated HCl, and evaporation to dryness.

• At this point the DMG has been destroyed– The samples can be re-dissolved in wash solution for

addition to a second Ni column, – or re-dissolved in dilute acid for a targeted resin

decontamination step, concentrated again, dissolved in wash solution, and added to the second Ni column.

Ni-59/63 Analysis RPP Supernate

• Two Ni columns, with a 0.04g Bio-Rad AMP-1 strike• Decontamination Factors

– Cs-137 8.5E+8– Tc-99 2.6E+5

• Ni Chemical Recoveries 63%

SRTC Shielded Analytical Cell

Ni-59/63 Analysis RPP Sludge

• 20 second remote batch contact with Ni Resin followed by a 0.04g Bio-Rad AMP-1 strike, and a second Ni Column

• Decontamination Factors– Sr-90/Y-90 >1E+8

– Cs-137 >5E+7

– Lanthanides >1E+5

– Co-60 >3E+3

Summary

• Developed a number of approaches to conducting radioactive Ni extractions for a wide variety of sample matrices based on the Eichrom Ni resin

• Future Ni work forseen in – evaluating other precursors to the Ni column (i.e.

Bio-Rad Chelex or Eichrom Ln) – exploring faster avenues for yielding the

separations