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Home , Actinide chemistry

and Repository Science Program in support of the Waste Isolation Pilot Plant (WIPP)

J-F. Lucchini, M. Borkowski, M.K. Richmann and D.T. Reed

Los Alamos National Laboratory, EES, Carlsbad Operations

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 The Waste Isolation Pilot Plant, WIPP, a cornerstone of the DOE' s cleanup effort, is designed to permanently dispose of defense- generated transuranic from research and production activities in the DOE weapons complex. The WIPP is located in southeastern New Mexico, 26 miles east of Carlsbad. Waste disposal operations began on March 26, 1999.

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Transuranic waste is shipped to the WIPP from many generator and storage sites such as Savannah River Site, Oak Ridge, Argonne, Rocky Flat, Idaho, Nevada Test Site, Livermore and Los Alamos. All shipments are done using specially designed TRUPAC-II containers.

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Disposal rooms are excavated in an ancient, stable salt formation 2,150 feet (almost one-half mile) underground. Transuranic waste, which consists of clothing, tools, rags, debris and other disposable items contaminated with radioactive elements, mostly , are emplaced in 55 gallon steel drums for permanent disposal.

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Waste and magnesium are placed in a WIPP Disposal Room. On March 23, 2006 the amount of 76,156 containers are disposed in the underground.

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 The Actinide Chemistry and Repository Science Program (ACRSP) is part of a larger multi-disciplinary Los Alamos group (EES-12) working in Carlsbad. We conduct our laboratory research programs at the Carlsbad Environmental Monitoring and Research Center, an institute that is operated by New Mexico State University. Our most important purpose is to provide laboratory research and program support on actinide-related issues to the DOE Carlsbad Field Office (CBFO) to maintain the certification of the WIPP. Additionally, we have the capability to conduct research programs in actinide for other sponsors.

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Glove boxes with controlled atmosphere

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Glove box for high radioactivity operation and LCS (behind)

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Hoods for work with low radioactivity samples

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 ICP-MS and Dr. Mike Richmann as operator

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Lab Capability:

™ ICP-MS designated for Pu and Am ™ Photo-acoustic with powerful laser ™ XRD (x-ray diffraction) ™ Spectroscopy (Cary 500) ™

™ CO2 analysis (down to ppb level) ™ Liquid Scintillation Counting

™ Glove boxes with controlled atmosphere (<0.1 ppm O2)

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 The Actinide Chemistry and Repository Science Program (ACRSP) is conducted according to five Test Plans approved by CBFO: ‰ /Stability of (VI) in WIPP • Solubility of U(VI) in WIPP brine • Redox stability of U(VI) in WIPP brine • Effect of radiolytic products on uranium speciation

‰ Plutonium (VI) Reduction by Iron • Limited scope - confirmatory study on effect of various form of iron, iron oxide on plutonium redox reaction

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 ‰ Neodymium (III) Solubility in WIPP Brine • Solubility of Nd(III) in WIPP brine, an analog for

Am(III) and Pu(III), studied as a function of pCH+ and concentration and measured from over-saturation and under-saturation

‰ Solubility/Stability in WIPP Brine • Solubility of Am(III) in WIPP brine • Effect of radiolytic products and repository components on americium oxidation and stability/solubility of Am higher oxidation states at the repository conditions

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 ‰ Plutonium Speciation and Solubility in the WIPP • Technical assessment of the current WIPP Database on Pu • Relevance of Pu(III) in the WIPP • Solubility of Pu(IV) in the WIPP • Reduction of Pu(V0 and Pu(VI) in the WIPP • Speciation of plutonium in the WIPP

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Two major programmatic groups can be distinguished:

1. Effect of radiolytic products of brine, microbial activity and repository components on redox speciation of plutonium, americium and uranium.

2. Solubility of transuranium elements in

WIPP brine (effect of pCH+, carbonate, organic ligands, etc.)

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Brine Composition Used in Actinide Solubility Studies MgCl2 NaCl ERDA-6 GWB simplified simplified Component g/L M/L g/L M/L g/L M/L g/L M/L NaCl 248.6 4.254 167.8 2.874 292.2 5.0

MgCl2.6H2O 3.667 0.018 193.4 0.953 751.9 3.704

Na2SO4 22.52 0.159 23.61 0.166 NaBr 1.074 0.010 2.565 0.025

Na B O .10H O 2 4 7 2 5.7 0.015 14.03 0.037 KCl 6.869 0.092 32.57 0.437 LiCl - - 0.174 0.004

CaCl2.2H2O 1.672 0.011 1.896 0.013 Ionic strength 4.965 M 6.839 M 11.1 M 5.0 M Density g/mL 1.183 1.216 1.252 1.185 GWB - Generic Weep Brine ERDA-6 - Energy Research and Development Administration Well 6

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 - Stability of H2O2 and OCl in brine

0.16 0.9 - t=0h Decomposition of H O in brine 0.14 OCl in 5 M NaCl t=6h 0.8 2 2 t=12h 0.12 t=18h 0.7 t=24h t=30h 0.6 0.10 t=36h t=42h 0.5 0.08 t=48h

GWB at pcH = 8.5 t=54h -0.012*t t=60h 0.4 y = 0.836*e 0.06 t=66h 0.3 0.04 Absorbance (rel. unit) Absorbance (rel. Absorbance at 351 nm at Absorbance 0.2 ERDA-6 at pcH = 9.0 -0.075*t 0.02 y = 0.789*e 0.1 0.00 0.0 0 20 40 60 80 100 120 140 160 180 250 275 300 325 350 375 400 Time, hours Wavelength (nm)

- - 2 OCl + H2O2 ' 2 Cl + H2O + O2 OCl- + Br- ' Cl- + OBr- + …

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Dependence of hypochlorite generation as a function of absorbed dose of α and NaCl concentration

0.006

0.005

5 m NaCl 0.004

0.003

4 m NaCl 0.002

3 m NaCl

Hypochlorite Concentration, M Concentration, Hypochlorite 0.001

2 m NaCl 0.000 0 100 200 300 400 500 600 Dose, (kGy)

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Primary G-values

calculated for different 0.06 chloride concentrations 0.05 Cl- 0.04 concentration, GH2O2 GClOH· [M]

0.03 5 0.23 0.55 4 0.27 0.50 0.02 5 M NaCl 3 0.32 0.44 Hypochlorite Saturation, M 0.01 2 0.40 0.38 0.00 012345678910111213 238Pu Activity, Ci/L

Kelm M., I. Pashalidis, I.J. Kim Applied Radiation and Isotopes, 51, (1999) 637-642.

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Effect of various forms of iron on plutonium (VI) reduction

in ERDA-6 brine at pCH+=9.2 and anoxic conditions

5x10-5 Reduction of Pu(VI) by Iron and Iron 4x10-5

3x10-5 Ferric oxide

2x10-5 Fe Powder

Fe Coupon 1x10-5 Pu concentration, M

0 Magnetite

0 100 200 300 400 500 600 Time in hours The presence of Fe0 and Fe2+ resulted in the rapid loss of plutonium from solution. In the case of ferric oxide some loss of Pu was noted, but residual concentrations remained high and it was (postulated) due to sorption not reduction/precipitation. The most complete and rapid loss of Pu occurred for magnetite which was the only iron phase that contained Fe2+. These results show that Fe0 and Fe2+ effectively remove dissolved plutonium from brine. ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 0.10 Pu(VI) in GWB Brine

0.08

0.06

0.04 Peak at 851 nm is hydrolyzed Pu(VI) Optical Density 0.02

0.00

300 400 500 600 700 800 900 Wavelength (nm)

The absorption spectrum of the plutonium in GWB brine. Since the pH is ~ 9, the plutonium is hydrolyzed (complexed with hydroxide) resulting in a 20 nm shift in the absorption maximum to 851 nm. The absorption spectrum of this solution was stable over the three-month period that it was monitored.

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Solubility of Nd(III) and U(VI) The goal of this research is to provide the experimental data for the solubility of trivalent and hexavalent . In this study neodymium (III) was used as a redox- invariant analog for Am (III) and Pu (III). The experiments in each approach are conducted in

GWB and ERDA-6 as a function of pCH+ and carbonate concentration. Simplified brine, 5 M NaCl, was used for comparison.

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Experimental limitations:

ƒ The highest concentration of carbonate ion in GWB and ERDA-6 brine, before the cloud point was observed, was determined to be 2- 4 x 10-2 M.

ƒ The highest pCH+ , before the cloud point was observed, was: - for Erda-6 was equal to 10.8, - for GWB brine was equal to 8.7.

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Low pCH+ limit and pCH+ vs. pH reading in ERDA-6 brine

Base/Acid in ERDA-6 Brine

10

Buffering 8 by sulfate 4

pH reading vs pcH for HP water

6

pH reading pH reading

4 2

2 Buffering by borate

pHread = 0.9998 * pcH - 0.9438

0 0 0.0 0.5 1.0 1.5 2.0 2.5 024 Volume of 1.00 M HCl, mL pCH+ calculated

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Low pCH+ limit and pCH+ vs. pH reading in GWB brine

Base/Acid Titration in GWB Brine

8 Buffering by sulfate

4 6 pH reading vs pcH for HP water

4

pH reading pH reading 2

2 Buffering by borate

pH = 0.9749 * pcH - 1.229 read 0 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 024 Volume of 1.00 M HCl, mL pC calculated H+

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 ERDA-6

•pCH+ range 7.5 – 12 • Initial carbonate concentrations: 0 (carbonate free), 10-5, 10-4, 10-3 and 10-2 M

•NdCl3 solution was used as a spike in the over-saturation approach • Initial Nd(III) concentration was 5x10-5 M and U(VI) was 1.7x10-5 M

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 ERDA-6 cont.

• NdOH(CO3) solid, prepared in our lab, was used in the under-saturation approach with carbonate

• Nd(OH)3 solid, commercial from Alfa Aesar, was used in the under-saturation approach without carbonate • All carbonate free experiments were conducted in the nitrogen glove box and carbonate ion was removed from the brine prior to the experiment

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Nd (III)

10-4 ERDA-6 kinetic of equilibration 10-5 oversaturation pC H+ - 8.0 - 9.0 -6

10 - 9.2

10-7 Nd Concentration, M

10-8 0 2 4 6 8 1012141618202224 Equilibration Time, days

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Nd (III) 1E-4 ERDA-6 carbonate free system 1E-5 over- and under-saturation

1E-6

1E-7

1E-8 Nd Concentration, M - oversaturation - undersaturation - trend 1E-9 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 pC H+

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Nd (III)

1E-4 over- under- carbonate - 10-2 M ERDA-6 - 10-3 M 1E-5 over- and under-saturation - 10-4 M with - 10-5 M - trend (no carb) 1E-6

1E-7

1E-8 Nd Concentration, M

1E-9 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 pC H+

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 U (VI) 10-2 pC =8 H+ -3 10 pC =9 ERDA-6 H+ pC =10 -4 carbonate free H+ 10 pC =11 H+ pC =12 10-5 H+

10-6

10-7

10-8 Uranium concentration, M 10-9 uranium 10-10 0 25 50 75 100 125 150 Time, Days

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 U (VI)

initial uranium concentration 10-5 ERDA-6 10-6

10-7

10-8 air atmosphere nitrogen atmosphere 10-9 uranium detection limit

Uranium concentration, M Uranium concentration, 10-10 89101112 pC H+

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 GWB

•pCH+ range 6.5 – 8.5 • Initial carbonate concentrations: 0 (carbonate free), 10-5, 10-4, 10-3 and 10-2 M

•NdCl3 solution was used as a spike in the over-saturation approach • Initial Nd(III) concentration was 5x10-5 M

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 GWB CONT.

• NdOH(CO3) solid, prepared in our lab, was used in the under-saturation approach with carbonate

• Nd(OH)3 solid, commercial from Alfa Aesar, was used in under-saturation approach without carbonate • All carbonate free experiments were conducted in the nitrogen glove box and carbonate ion was removed from the brine prior to the experiment

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Nd (III) 1E-4 GWB over- and under-saturation 1E-5 with carbonates

1E-6

1E-7 over- under- carbonate - 10-2 M - 10-3 M 1E-8 -4 Nd Concentration, M - 10 M - 10-5 M - trend

1E-9 6.0 6.5 7.0 7.5 8.0 8.5 9.0 pC H+

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Nd (III)

1E-4 GWB over- and under-saturation 1E-5 carbonate free

1E-6

1E-7

1E-8 Nd Concentration, M - oversaturation - undersaturation - carbonate trend

1E-9 6.0 6.5 7.0 7.5 8.0 8.5 9.0 pC H+

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 U (VI)

10-3 pC =6 GWB H+ pC =7 carbonate free H+ pC =8 10-4 H+ pC =9 H+

10-5

10-6 Uranium concentration, M

10-7 0 25 50 75 100 125 150 Time, Days

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 U (VI) GWB 1E-4 carbonate free over-saturation

1E-5

1E-6 Uranium concentration, M

1E-7 6.0 6.5 7.0 7.5 8.0 8.5 9.0 pC H+

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 5 M NaCl

•pCH+ range 8.0 – 13.0 • Initial carbonate concentrations: 0 (carbonate free), 10-5, 10-4, 10-3 and 10-2 M

•NdCl3 solution was used as a spike in the over-saturation approach • Initial Nd(III) concentration was 5x10-5 M

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Nd (III) 1E-4 5 M NaCl 1E-5 over- and under-saturation carbonate free

1E-6 - oversaturation - undersaturation - trend

1E-7

1E-8 Nd Concentration, M

1E-9 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5 13.0 pC H+

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Conclusions: The solubility experiments are still going on but preliminary conclusions can be made. ƒ The trend in Nd(III) solubility measured as a function of pCH+ in 5 M NaCl is in good agreement with literature data, however measured solubility is slightly higher than those reported in lower concentrations of NaCl. ƒ Nd(III) and U(VI) are greater in GWB brine than in ERDA-6 brine. ƒ The neodymium data obtained from over-saturation experiments is very close to data obtained from under- saturation experiments. It means that in many cases a steady state was achieved. ƒ Almost no effect of carbonate on Nd(III) solubility was observed.

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006 Conclusions:

The following Nd(III) solubilities at pCH+ = 8.5 were measured:

With carbonate No carbonate ERDA-6 2 x 10-8 M 4 x 10-8 M GWB 3 x 10-7 M3 x 10-7 M

Calculated* : Estimated with Estimated with Microbial Presence Microbial Absence Castile Brine 1.69 x 10-7 M 1.77 x 10-7 M Salado Formation Brine 3.07 x 10-7 M 3.07 x 10-7 M

*Brush L.H., and Xiong Y. Actinide Solubility for the WIPP PAB Calculations, unpublished analysis (2005)

ANS 14th Biennial Topical Meeting LA-UR 05-9615 Carlsbad, April 3-6, 2006