Jack L. Ryan

The solubility of uranium(IV) hydrous oxide in sodium hydroxide solutions under reducing conditions

Abstract The solubility of hydrous UO2 in sodium hydroxide solutions containing sodium dithionite and/or Zn metal powder as reductants has been measured. The results provide no firm evidence for any amphoteric behavior of U(IV) but do set an upper limit of K ≤ 2 x 10−23 for the hypothetical reaction: The results provide no evidence for such a reaction.

Alpha radiation induced production of HNO3 during dissolution of Pu compounds (1)

Abstract Air-equilibrated suspensions of 238 Pu and 239 Pu compounds in dilute salt solutions produced HNO 3 at a rate which increased with the H + concentration.

Aqueous Chemistry of Nd in Borosilicate-Glass/Water Systems

Phosphate and nonphosphate glass suspensions in water were adjusted to a pH range between 1 and 10 and equilibrated in Ar(g) and C02(g) to determine the specific chemical reactions controlling the aqueous concentrations of Nd. The Nd concentrations in solutions contacting nonphosphate glass equilibrated under Ar(g) and 0.00154 atm C02(g) were controlled by Nd(OH)3(gl) and Nd0HC03(c), respectively. The Nd concentrations in solutions contacting phosphate glass equilibrated under Ar(g) or 0.00154 atm C02(g) at pH values >5.5 were <10~ · M and the observed low concentrations, when compared with nonphosphate glass, are the result of an as yet unidentified Nd phosphate compound. The limited data on La, Sm, and Am, as expected, show that their aqueous behavior in these systems is similar to Nd.

Solubility constraint: an important consideration in safety assessment of nuclear waste disposal

Solubilities of key solid compounds that are either present in the waste form or can readily precipitate from waste package leachates under repository conditions can be used to set maximum limits on radionuclide concentrations expected in ground water. This is because the solubility limited concentrations are independent of the release scenarios, hydrologic transport characteristics, and absorption-desorption reactions. Some of the important factors that control solubilities are pH, pe, type of solid phase, and nature of complexing ligands in the ground waters. Most of the above factors are affected by radiolysis due to the inherent radiation field of the waste form. Experimental results pertaining to the solubilities of selected Am, U, Np, and Pu compounds and the effects of radiolysis are discussed. These results show that: (1) at expected repository pH and reducing conditions, solubility controlled concentrations of several actinides are low and near acceptable limits, (2) the redox conditions at the waste form-water interface may be very oxidizing due to radiolytic effects, despite the fact that normal repository conditions are assumed to be reducing, (3) additional data on solubility limits and key thermodynamic parameters are needed. 26 references, 4 figures.