Advances in understanding cesium retention on calcium silicate material

Area of Science:

• Nuclear Chemistry
• Materials Science
• Environmental Science

Background:

• Cesium, a radiologically significant fission product, poses long-term radioactivity and environmental fate concerns in nuclear reactors.
• Cesium retention in nuclear reactor structural materials, specifically calcium silicate thermal insulators, is a critical issue during simulated accidents.

Purpose of the Study:

• To investigate the chemical compound of cesium trapped in calcium silicate thermal insulators under simulated nuclear accident conditions.
• To overcome characterization challenges using conventional X-ray diffraction analysis.

Main Methods:

• Employed a combined pre- and post-water dissolution analysis technique.
• Utilized infrared (IR) spectroscopy and optical emission spectroscopy (OES) for material characterization.
• Analyzed dissolved cesium and silicon molar ratios in leaching water.

Main Results:

• Identified cesium metasilicate (Cs₂SiO₃) as the water-soluble cesium compound formed in calcium silicate materials after high-temperature reactions.
• Confirmed Cs₂SiO₃ formation through vibrational characteristics and a dissolved Cs:Si molar ratio of 2.16 ± 0.33.
• Found that 79-98% of retained cesium at 700-800°C was in the form of Cs₂SiO₃, indicating its stability and prevalence.

Conclusions:

• Cesium metasilicate (Cs₂SiO₃) is the dominant cesium compound formed in calcium silicate insulators under accident conditions.
• Thermodynamic analysis supports the stability of Cs₂SiO₃ over other cesium silicates.
• The volatility of Cs₂SiO₃ poses a significant environmental risk, potentially spreading via water leaks from damaged reactors.