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Sorption of Np and Te in underground waters by uranium oxidesстатья
Информация о цитировании статьи получена из
Scopus
Дата последнего поиска статьи во внешних источниках: 28 мая 2015 г.
- Авторы: Kazakovskaya T.V., Shapovalov V.I., Kushnir N.V., Zakharova E.V., Kalmykov S.N., Batuk O.N., Haire M.J.
- Журнал: Proceedings of the 11th International High Level Radioactive Waste Management Conference, IHLRWM
- Том: 2006
- Год издания: 2006
- Первая страница: 379
- Последняя страница: 384
- Аннотация: The production of nuclear fuels results in the accumulation of large quantities of depleted uranium (DU) in the form of uranium hexafluoride (UF 6), which is converted to uranium oxides. Depleted uranium dioxide (DUO 2) can be used as a component of radiation shielding and as an absorbent for migrating radionuclides (especially 237Np and 99Tc). These may emerge from casks containing spent nuclear fuel (SNF) that are stored for hundreds of thousands of years in high-level wastes (HLW) and SNF repositories (e.g. Yucca Mountain Project). In this case DU oxides serve as an additional engineered chemical barrier. This work is a pan of the joint Russian -American Program on Beneficial Use of Depleted Uranium. This paper describes the UO 2 transformations that take place in contact with various aqueous media (deionized water (DW), J-13 solution that simulates Yucca Mountain ground water, etc.) and sorption of long-lived radionuclides ( 237Np and 99Tc)from these media by depleted uranium dioxide. Samples of depleted uranium dioxide used in this work originated from the treatment of UF 6 in a reducing media to form UO 2 (DUO 2-1 at 600°C, DUO 2-2 at 700°C, and DUO 2-3 at 800°C). The investigations on DUO 2 transformations were performed under dynamic and static conditions. Increasing the DUO 2 pretreatment temperature resulted information of less oxidized uranium compounds. Under static conditions the solubility of the DUO 2 samples in J-13 solution is considerably higher than in DW. When the pretreatment temperature is decreased, the solubility of DUO 2 samples raises regardless of the media. The experiments on interaction between depleted uranium dioxide and aqueous media (DW and J-13 solution) under dynamic conditions demonstrated that during 30-40 days the penetration / filtration rate of DW and J-13 solution through a thin DUO 2 layer decreased dramatically, and then slowed and stabilized. This can be explained by the forming of a secondary particulate phase that clogs the pores and reduces the filtration capacity. The filtration rate of J-13 solution through DUO 2 layer is several times lower than that of DW. The sorption of neptunium in two valence states - Np(IV) and Np(V)- was also investigated. Various species of depleted uranium dioxide sorb Np(V) and Np (IV) from aqueous media. Equilibrium was achieved in 24 hours for Np (V) and in 2 hours for Np (IV). Increasing the pretreatment temperature leads to increased sorption. Np(V) sorption is accompanied with partial reduction of Np(V) to Np(IV), while Np (IV) sorption onto DUO 2 is accompanied by its partial oxidation to Np (V). Increasing the temperature up to 95°C intensifies sorption. The sorption of Np(V) onto DUO 2 surfaces is irreversible. Finally, Tc sorption experiments were carried out for two valence states of technetium - Tc(VII) and Tc(IV). There was no significant sorption of Tc(VU)from DW and J-13 solution: However, depleted uranium oxide sorption of Tc(TV)from aqueous solutions was observed. In the pH range from 2.5 to 6, Tc(IV) sorption increases from 30 to 80%, while in neutral medium, sorption increases to 90%. Experimental results obtained indicate that depleted uranium oxide can be successfully used as an additional chemical barrier in HLW and SNF repositories.
- Добавил в систему: Калмыков Степан Николаевич