Plutonium Migration during the Leaching of Cemented Radioactive Waste Sludges

Law, Kathleen A.; Parry, Stephen; Bryan, Nicholas D.; Heath, Sarah L.; Heald, Steven M.; Knight, Darrell; O’Brien, Luke; Fuller, Adam; Bower, William; Law, Gareth; Livens, Francis

doi:10.3390/geosciences9010031

Title: Plutonium Migration during the Leaching of Cemented Radioactive Waste Sludges

Journal Article · Tue Jan 08 00:00:00 EST 2019 · Geosciences

DOI:https://doi.org/10.3390/geosciences9010031· OSTI ID:1491807

Law, Kathleen A. ^[1]; Parry, Stephen ^[1]; Bryan, Nicholas D. ^[2]; Heath, Sarah L. ^[1]; Heald, Steven M. ^[3];

^[1]; O’Brien, Luke ^[4]; Fuller, Adam ^[1]; Bower, William ^[5]; Law, Gareth ^[6]; Livens, Francis ^[1]

Univ. of Manchester (United Kingdom)
Univ. of Manchester (United Kingdom); National Nuclear Laboratory, Warrington (United Kingdom)
Argonne National Lab. (ANL), Argonne, IL (United States)
National Nuclear Laboratory, Warrington (United Kingdom)
University of Helsinki (Finland)
Univ. of Manchester (United Kingdom); University of Helsinki (Finland)

One of the most challenging components of the UK nuclear legacy is Magnox sludge, arising from the corrosion of Mg alloy-clad irradiated metallic U fuel that has been stored in high pH ponds. The sludges mainly comprise Mg hydroxide and carbonate phases, contaminated with fission products and actinides, including Pu. Cementation and deep geological disposal is one option for the long-term management of this material, but there is a need to understand how Pu may be leached from the waste, if it is exposed to groundwater. Here, we show that cemented Mg(OH)₂ powder prepared with Pu(IV)_aq is altered on contact with water to produce a visibly altered ‘leached zone’, which penetrates several hundred microns into the sample. In turn, this zone shows slow leaching of Pu, with long-term leaching rates between 1.8–4.4 × 10^-5% of total Pu per day. Synchrotron micro-focus X-ray fluorescence mapping identified decreased Pu concentration within the ‘leached zone’. A comparison of micro-focus X-ray absorption spectroscopy (µ-XAS) spectra collected across both leached and unleached samples showed little variation, and indicated that Pu was present in a similar oxidation state and coordination environment. Fitting of the XANES spectra between single oxidation state standards and EXAFS modeling showed that Pu was present as a mixture of Pu(IV) and Pu(V). The change in Pu oxidation from the stock solution suggests that partial Pu oxidation occurred during sample ageing. Similarity in the XAS spectra from all samples, with different local chemistries, indicated that the Pu oxidation state was not perturbed by macro-scale variations in cement chemistry, surface oxidation, sample aging, or the leaching treatment. These experiments have demonstrated the potential for leaching of Pu from cementitious waste forms, and its underlying significance requires further investigation.

View Accepted Manuscript (DOE)

Cite

Export

Save

Research Organization:: Argonne National Lab. (ANL), Argonne, IL (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Basic Energy Sciences (BES)

Grant/Contract Number:: AC02-06CH11357

OSTI ID:: 1491807

Journal Information:: Geosciences, Vol. 9, Issue 1; ISSN 2076-3263

Publisher:: MDPICopyright Statement

Country of Publication:: United States

Language:: English

References (17)

ATHENA , ARTEMIS , HEPHAESTUS : data analysis for X-ray absorption spectroscopy using IFEFFIT Ravel, B.; Newville, M. Journal of Synchrotron Radiation, Vol. 12, Issue 4 https://doi.org/10.1107/S0909049505012719	journal	June 2005
Probing the microstructure and water phases in composite cement blends Gorce, Jean-Philippe; Milestone, Neil B. Cement and Concrete Research, Vol. 37, Issue 3 https://doi.org/10.1016/j.cemconres.2006.10.007	journal	March 2007
Characterisation of plutonium species in alkaline liquors sampled from a UK legacy nuclear fuel storage pond Gregson, Colin R.; Hastings, Jeremy J.; Sims, Howard E. Analytical Methods, Vol. 3, Issue 9 https://doi.org/10.1039/c1ay05313b	journal	January 2011
Solubility and hydrolysis of tetravalent actinides Neck, Volker; Kim, J. I. Radiochimica Acta, Vol. 89, Issue 1 https://doi.org/10.1524/ract.2001.89.1.001	journal	January 2001
Calcium carbonate efflorescence on Portland cement and building materials Dow, C.; Glasser, F. P. Cement and Concrete Research, Vol. 33, Issue 1 https://doi.org/10.1016/S0008-8846(02)00937-7	journal	January 2003
Analysis of calcium leaching behavior of plain and modified cement pastes in pure water Jain, Jitendra; Neithalath, Narayanan Cement and Concrete Composites, Vol. 31, Issue 3 https://doi.org/10.1016/j.cemconcomp.2009.01.003	journal	March 2009
Properties of cement systems containing intermediate level wastes Palmer, J. D.; Fairhall, G. A. Cement and Concrete Research, Vol. 22, Issue 2-3 https://doi.org/10.1016/0008-8846(92)90072-4	journal	March 1992
The PNC/XOR X-ray microprobe station at APS sector 20 Heald, S. M.; Cross, J. O.; Brewe, D. L. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 582, Issue 1 https://doi.org/10.1016/j.nima.2007.08.109	journal	November 2007
Discharges to the environment from the Sellafield site, 1951-1992 Gray, J.; Jones, S. R.; Smith, A. D. Journal of Radiological Protection, Vol. 15, Issue 2 https://doi.org/10.1088/0952-4746/15/2/001	journal	June 1995
Protective or damage promoting effect of calcium carbonate layers on the surface of cement based materials in aqueous environments Schwotzer, M.; Scherer, T.; Gerdes, A. Cement and Concrete Research, Vol. 40, Issue 9 https://doi.org/10.1016/j.cemconres.2010.05.001	journal	September 2010
Real-space multiple-scattering calculation and interpretation of x-ray-absorption near-edge structure Ankudinov, A. L.; Ravel, B.; Rehr, J. J. Physical Review B, Vol. 58, Issue 12 https://doi.org/10.1103/PhysRevB.58.7565	journal	September 1998
Plutonium(III,IV,VI) speciation in Gorleben groundwater using XAFS Dardenne, Kathy; Seibert, Alice; Denecke, Melissa A. Radiochimica Acta, Vol. 97, Issue 2 https://doi.org/10.1524/ract.2009.1581	journal	January 2009
Combined electron microscopy and vibrational spectroscopy study of corroded Magnox sludge from a legacy spent nuclear fuel storage pond Gregson, Colin R.; Goddard, David T.; Sarsfield, Mark J. Journal of Nuclear Materials, Vol. 412, Issue 1 https://doi.org/10.1016/j.jnucmat.2011.02.046	journal	May 2011
The encapsulation of Mg(OH)2 sludge in composite cement Collier, N. C.; Milestone, N. B. Cement and Concrete Research, Vol. 40, Issue 3 https://doi.org/10.1016/j.cemconres.2009.10.007	journal	March 2010
XANES identification of plutonium speciation in RFETS samples LoPresti, V.; Conradson, S. D.; Clark, D. L. Journal of Alloys and Compounds, Vol. 444-445 https://doi.org/10.1016/j.jallcom.2006.10.101	journal	October 2007
Structure of early actinides(V) in acidic solutions Di Giandomenico, M. V.; Naour, C. Le; Simoni, E. Radiochimica Acta, Vol. 97, Issue 7 https://doi.org/10.1524/ract.2009.1620	journal	January 2009
Solubility and hydrolysis of tetravalent actinides Neck, V.; Kim, J. I. Karlsruhe https://doi.org/10.5445/ir/270045805	text	January 1999