Curium analysis in plutonium uranium mixed oxide by x-ray fluorescence and absorption fine structure spectroscopy

Area of Science:

• Nuclear Chemistry
• Materials Science
• Spectroscopy

Background:

• Mixed oxide (MOX) fuels containing plutonium and uranium are utilized in commercial nuclear reactors.
• Post-irradiation analysis of actinides is crucial for understanding fuel behavior and environmental interactions.

Purpose of the Study:

• To investigate the local occurrence, speciation, and coordination environment of curium (Cm) within irradiated MOX fuel.
• To determine the chemical state and distribution of curium in different zones of the fuel pellet.

Main Methods:

• Employing micro-X-ray fluorescence (µ-XRF) and micro-X-ray absorption fine structure (µ-XAFS) spectroscopy.
• Analyzing an irradiated MOX sample with an average burn-up of 60 MW d kg(-1).

Main Results:

• Curium concentration is higher in the fuel center (≈0.7 wt%) than the rim (≈0.03 wt%), attributed to volatile oxide condensation.
• Curium predominantly exists as Cm(3+) species (>90%) in a [CmO8](13-) or [CmO7](11-) coordination environment.
• Minimal Cm(IV) (<10%) was detected in the rim zone, indicating reduction due to the uranium dioxide matrix.

Conclusions:

• The uranium dioxide matrix influences curium speciation, promoting its reduction to Cm(3+).
• Curium's distribution and speciation are affected by temperature gradients and the redox environment within the MOX fuel.