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

Abstract

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 thatmore » 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.« less

Authors:
 [1];  [1];  [2];  [1];  [3]; ORCiD logo [1];  [4];  [1];  [5];  [6];  [1]
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  1. Univ. of Manchester (United Kingdom)
  2. Univ. of Manchester (United Kingdom); National Nuclear Laboratory, Warrington (United Kingdom)
  3. Argonne National Lab. (ANL), Argonne, IL (United States)
  4. National Nuclear Laboratory, Warrington (United Kingdom)
  5. University of Helsinki (Finland)
  6. Univ. of Manchester (United Kingdom); University of Helsinki (Finland)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
OSTI Identifier:
1491807
Grant/Contract Number:  
AC02-06CH11357
Resource Type:
Accepted Manuscript
Journal Name:
Geosciences
Additional Journal Information:
Journal Volume: 9; Journal Issue: 1; Journal ID: ISSN 2076-3263
Publisher:
MDPI
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; plutonium; radioactive waste; speciation; cement; leaching

Citation Formats

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, and Livens, Francis. Plutonium Migration during the Leaching of Cemented Radioactive Waste Sludges. United States: N. p., 2019. Web. doi:10.3390/geosciences9010031.
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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. Plutonium Migration during the Leaching of Cemented Radioactive Waste Sludges. United States. https://doi.org/10.3390/geosciences9010031
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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, and Livens, Francis. Tue . "Plutonium Migration during the Leaching of Cemented Radioactive Waste Sludges". United States. https://doi.org/10.3390/geosciences9010031. https://www.osti.gov/servlets/purl/1491807.
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@article{osti_1491807,
title = {Plutonium Migration during the Leaching of Cemented Radioactive Waste Sludges},
author = {Law, Kathleen A. and Parry, Stephen and Bryan, Nicholas D. and Heath, Sarah L. and Heald, Steven M. and Knight, Darrell and O’Brien, Luke and Fuller, Adam and Bower, William and Law, Gareth and Livens, Francis},
abstractNote = {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.},
doi = {10.3390/geosciences9010031},
journal = {Geosciences},
number = 1,
volume = 9,
place = {United States},
year = {2019},
month = {1}
}
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Journal Article:
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https://doi.org/10.3390/geosciences9010031
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Figures / Tables:

Table 1. Table 1.: Summary of Pu-containing sample preparation and pre-treatment. Samples containing 239Pu were used for leaching experiments, while those containing 242Pu were used for spectroscopic studies. Leached and unleached examples of the 242Pu-containing samples were prepared.
All figures and tables (10 total)
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    Table 1. (p. 3)table
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    Table 2. (p. 8)table
    Figure 5. (p. 9)figure
    Figure 6. (p. 10)figure
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    Table 3. (p. 11)table
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