Migration of Neptunium and Plutonium in Hydrofracturing Disposal

Neptunium and plutonium are two important elements in middle radioactive wastes for the present study. The speciations of the elements in groundwater and the interactions between watershale, watercement in the potential area of hydrofracturing disposal of China are simulated by using geochemical modeling code EQ3/6. The simulated results are as follows:1) The main species are NpO2(CO3)34-, NpO2(CO3)23-, NpO2CO3- and NpO2(CO3)35- for Np, and PuO2(CO3)2-2 and Pu(OH)5- for Pu, even some of them rarely occurs in the case of nature and experiment;2) The equilibrium of interaction among species of groundwater in this potential areas of China have been reached;3) The watercement interaction process can divided into two stages, the fast stage with a high reaction rate during the initiative 10 d, and consequential slow stage 10 d later with a increased pH values due to the dissolved and deposited of the alkaline substance, the equilibrium of interaction between groundwater and cement have reached after 71 d;4) Both Np and Pu are almost immobile in the cement but they would release into the groundwater when the cement dissolved and damaged. The calculated activities of Am, Np, Pu in the equilibrium aqueous of watercement are 12.66, 1.405, 132.48 Bq,respectively. 