Solubility Controls on Releases

The perfect high-level waste repository (or toxic-waste site) is one in which individual waste components are at thermodynamic equilibrium with the host water-rock system. For such conditions there is no tendency for the waste components to dissolve and be transported from the site to the accessible environment. It was shown earlier that low-Eh crystalline-rock groundwaters are often near saturation with respect to UO2 (Section 13.2.3). Spent fuel UO2 in such a system should have little or no tendency to dissolve and release other radionuclides to the groundwater. An appropriate first task in characterizing a potential repository site should, therefore, be to obtain accurate groundwater analyses to determine if the groundwater is saturated with respect to UO2. 

Using MINTEQA2, it is interesting to compute the solubilities of Am, Np, Pu, Tc, Th, and U in low-Eh Swedish groundwater (SKI-90) and in the high-Eh waters from Yucca Mountain in the 

These maximum possible concentrations must be known to help define the source term or concentrations at a failed waste package, to permit modeling and prediction of the effects of radionuclide releases on future repository performance. 

Ml is important to note that the different radioisotopes of an element such as U or Pu share its solubility in proportion to their relative concentrations. 

Actinides and Their Daughter and Fission Products Chap. 13 

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