Dissolved Concentration Limits of Elements with Radioactive Isotopes
| Attachment | Size |
|---|---|
| ANL-WIS-MD-000010_REV06_Final.doc (34.02 MB) | 34.02 MB |
| ANL-WIS-MD-000010_REV06_Final_APPs.doc (10.55 MB) | 10.55 MB |
The purpose of this study is to evaluate dissolved concentration limits (also referred to as solubility limits) of elements with radioactive isotopes under probable repository conditions, based on geochemical modeling calculations using geochemical modeling tools, thermodynamic databases, field measurements, and laboratory experiments.
The scope of this activity is to predict dissolved concentrations or solubility limits for elements with radioactive isotopes (actinium, americium, carbon, cesium, chlorine, iodine, lead, neptunium, plutonium, protactinium, radium, selenium, strontium, technetium, thorium, tin, and uranium) relevant to calculated dose. Model outputs for uranium, plutonium, neptunium, thorium, americium, protactinium, and tin are provided in the form of tabulated functions with pH and log fCO2 as independent variables, plus one or more uncertainty terms. The radium model is presented as a constant solubility limit value over a range in pH. The solubility limits for the remaining elements are in the form of single values. Even though selection of an appropriate set of radionuclides documented in Radionuclide Screening (SNL 2007 [DIRS 177424]) includes actinium and lead, transport of actinium and lead are not modeled in the total system performance assessment (TSPA) for the license application (LA) model because of extremely short half lives (around 22 years). Actinium dose is calculated in the TSPA-LA by assuming secular equilibrium with 231Pa (Section 6.10). Lead dose effects are calculated in TSPA-LA by assuming secular equilibrium with 226Ra (Section 6.13). Therefore, actinium and lead are not analyzed in this report.
The output data from this report are fundamental inputs for TSPA LA used to determine the estimated release of these elements from waste packages and the Engineered Barrier System.
Consistent modeling approaches and environmental conditions were used to develop solubility models for the actinides discussed in this report. These models cover broad ranges of environmental conditions, so they are applicable to both waste packages and the invert. Uncertainties from thermodynamic data, water chemistry, temperature variation, and activity coefficients have been quantified or otherwise addressed.
