Oxidative dissolution of Cr-doped UO₂ nuclear fuel

Area of Science:

• Nuclear Engineering
• Materials Science
• Geochemistry

Background:

• Alternative nuclear fuels, specifically chromium (Cr)-doped uranium dioxide (UO2), are utilized in light-water reactors.
• Understanding the dissolution behavior of these advanced fuels is crucial for assessing their long-term performance and safety in geological disposal facilities.

Purpose of the Study:

• To investigate the influence of Cr doping on the dissolution rate of UO2 nuclear fuel under various conditions.
• To elucidate the mechanisms governing the dissolution kinetics of Cr-doped UO2 in simplified groundwater solutions.

Main Methods:

• Dissolution experiments were conducted on Cr-doped UO2 across a range of Cr concentrations in a simplified groundwater simulant.
• Experiments were performed under oxic conditions at temperatures of 25, 40, and 60°C.
• Analysis included identifying secondary phases and determining activation energies to understand dissolution mechanisms.

Main Results:

• Cr doping systematically reduced the normalized dissolution rate of uranium (U) at 25 and 40°C, particularly in dilute solutions, attributed to galvanic coupling between Cr and U.
• At solution saturation, U dissolution rate was independent of Cr content, with schoepite and Na2U2O7·6H2O identified as secondary phases.
• At 60°C, the trend reversed, with U dissolution increasing with Cr content, indicating other factors like U solubility and bicarbonate interactions become dominant.

Conclusions:

• Cr doping in UO2 nuclear fuel generally reduces uranium dissolution rates at lower temperatures through galvanic coupling, with increased grain size also contributing to reduced dissolution.
• At higher temperatures, other factors significantly influence dissolution kinetics, overriding the effect of Cr doping.
• Overall, Cr-doped UO2 exhibits comparable dissolution kinetics to undoped UO2, supporting its suitability for geological disposal.