Hydroxide Conversion Route for (U,Pu)O_2±x Nuclear Fuel Production

Area of Science:

• Nuclear Materials Science
• Solid-State Chemistry
• Ceramic Engineering

Background:

• Mixed oxide (MOX) fuels containing uranium (U) and plutonium (Pu) are crucial for advanced nuclear reactors.
• Achieving high cationic homogeneity in MOX fuels is essential for predictable performance and safety.
• Hydroxide coprecipitation is a key synthesis route for MOX fuel fabrication.

Purpose of the Study:

• To synthesize U_0.86Pu_0.14O_2±x solid solutions using hydroxide coprecipitation.
• To evaluate the impact of different precipitation methods on cationic homogeneity and microstructure.
• To assess the influence of plutonium content on the physicochemical and sintering behavior of MOX powders.

Main Methods:

• Hydroxide coprecipitation of U(IV) and Pu(IV) or Pu(III) from nitric acid solutions.
• Calcination and sintering of oxide precipitates at 1700 °C under Ar-4.3 vol% H₂.
• Comparison of three precipitation routes: simultaneous U(IV)-Pu(IV), simultaneous U(IV)-Pu(III), and premixed U(IV)-Pu(III).

Main Results:

• All precipitation methods resulted in highly uniform U and Pu distribution, exceeding homogeneity from other routes.
• Distinct microstructures and sintering capabilities were observed despite macroscopic similarity.
• Plutonium content significantly influenced the physicochemical and sintering properties of the synthesized MOX powders.

Conclusions:

• Hydroxide coprecipitation is a robust method for achieving excellent cationic homogeneity in MOX fuels.
• Microstructure and sintering behavior are sensitive to the precipitation method and Pu content.
• The findings provide valuable insights for optimizing MOX fuel fabrication processes.