Effect of uranium solubility on release rates from the proposed Yucca Mountain repository

The sensitivity of the release of radionuclides from the engineered barrier system in the proposed Yucca Mountain Repository to the solubility of uranium is investigated. Factors ranging from 0.1 up to 100 were applied to the nominal uranium solubility assumed in one of the TSPA models used in support of the site recommendation for the repository. At times earlier than about 50,000 years, the release rate of uranium is proportional to the change in the solubility. By 100,000 years, the proportionality continues to hold when the solubility is reduced, but when the solubility is increased, the release rate changes by a factor less than the factor applied to the solubility. At times beyond about 300,000 years, when the solubility is varied from 0.1 to 100 times its nominal value, the release rate changes by less than a factor of 20. Over the same range of changes in the uranium solubility, changes in the release rates of uranium decay products are less than a factor of three. Because uranium and its decay products make relatively small contributions to the dose rate, the changes in the dose rate at a well located 20 km from the repository are estimated to be less than 20%