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Radiolysis of water is a phenomenon which alters the prevailing conditions in the nearfield of a final geological repository for high-level nuclear waste (HLW), because the nominally anoxic conditions in the repository may change due to the production of oxidants close to the solid-liquid interface of the fuel, caused by the alpha radiolysis of water.

The influence of water chemistry and oxidant concentration in the liquid phase was tested by experiments which simulate chemical radiolysis effects. Uranium concentrations showed an unexpected behaviour; at low H(2)O(2) concentrations in solution, U concentrations were highest. U concentrations in the groundwater leachates were always lower than in pure water. The SEM-EDX examination showed the presence of different alteration phases on the sample. All alteration phases were found to contain only U (and possibly O, H, and C also). A reaction mechanism is proposed for the oxidation reactions taking place under the various conditions. Comparisons with natural analogues and previous work are made, and geochemical solubility limits of possible newly formed substances are examined. The results suggest that different polymorphs of uranium(IV) oxyhydroxides (para-, meta-schoepite, hemihydrate) and of uranium(VI) peroxide (Studtite, meta-studtite) have formed, and that in the case of the samples treated with groundwater, a scavenging mechanism, possibly controlled by an ion present in groundwater, leads to the deactivation of H(2)O(2) in the solution.

Additional information

Authors: AMME M, European Commission, Joint Research Centre, Institute for Transuranium Emements, Karlsruhe (DE)
Bibliographic Reference: An article published in: Radiochimica Acta, 2002, Volume 90, Issue 07, pp. 399
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Record Number: 200215695 / Last updated on: 2002-12-23
Original language: en
Available languages: en