Radiation Sensitivity of Natural Organic Matter: Clay Mineral Association Effects in the Callovo-Oxfordian Argillite

Journal Article · Thu Jan 01 04:00:00 EST 2009 · Journal of Electron Spectroscopy and Related Phenomena

DOI:https://doi.org/10.1016/j.elspec.2008.05.007· OSTI ID:980423

Schäfer, T; Michel, P; Claret, F; Beetz, T; Wirick, S; Jacobsen, C

Clay-rich low-organic carbon formations (e.g., Callovo-Oxfordian argillite in France and Opalinus Clay in Switzerland) are considered as host rocks for radioactive waste disposal. The clay-organic carbon has a strong impact on the chemical stability of the clays. For this reason, the nature of the clay-organic carbon, the release of hydrophilic organic compounds, namely, humic (HA) and fulvic acids (FA) and the radiation sensitivity of the undisturbed host rock organics was investigated. The clay sample originates from Oxfordian argillite (447 m depth, borehole EST 104). HA and FA were extracted following the standard International Humic Substance Society (IHSS) isolation procedure. Synchrotron based (C-, K-, Ca-, O- and Fe-edge XANES) scanning transmission X-ray microscopy (STXM) and FT-IR microspectroscopy was used to identify under high spatial resolution the distribution of clay-organic matter with different functionality using principal component and cluster analysis. The results show that in this old (Jurassic) geological formation, small parts of the organic inventory (1-5%) keeps the structure/functionality and can be mobilized as hydrophilic humic substance type material (HA and FA). Target spectra analysis shows best correlation for isolated humic acids with organics found in smectite-rich regions, whereas the extractable FA has better spectral similarities with the illite mixed layer minerals (MLM) regions. After radiation of 1.7 GGy under helium atmosphere the same rock sample area was investigated for radiation damage. Radiation damage in the smectite and illite-MLM associated organic matter is comparably low with 20-30% total oxygen mass loss and 13-18% total carbon mass loss. A critical dose dc of 2.5 GGy and a optical density after infinite radiation (OD?) of 54% was calculated under room temperature conditions. C(1s) XANES show a clear increase in Cdouble bond; length as m-dashC bonds especially in the illite-MLM associated organics. This results suggests a combination of the formation of Cdouble bond; length as m-dashC bond due to crosslinking via polymerization and mass loss due to bond breaking (scissioning) in the main chain or in side groups of the organic macromolecules upon irradiation.

• Research Organization: Brookhaven National Laboratory (BNL) National Synchrotron Light Source
• Sponsoring Organization: Doe - Office Of Science
• DOE Contract Number: AC02-98CH10886
• OSTI ID: 980423
• Report Number(s): BNL--93341-2010-JA
• Journal Information: Journal of Electron Spectroscopy and Related Phenomena, Journal Name: Journal of Electron Spectroscopy and Related Phenomena Vol. 170; ISSN JESRAW; ISSN 0368-2048
• Country of Publication: United States
• Language: English

Related Subjects

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
ARGILLITE
CARBON
CLAYS
FULVIC ACIDS
HUMIC ACIDS
ILLITE
MATTER
MINERALS
ORGANIC COMPOUNDS
ORGANIC MATTER
RADIATIONS
RADIOACTIVE WASTE DISPOSAL
SENSITIVITY
SPATIAL RESOLUTION
national synchrotron light source