Local measurement of bulk thermal diffusivity using photothermal radiometry

Area of Science:

• Materials Science
• Nuclear Engineering
• Thermal Physics

Background:

• Irradiated nuclear fuels (e.g., uranium oxide) and moderator materials (e.g., graphite) become friable, necessitating characterization techniques for irregularly shaped fragments.
• Accurate measurement of thermal diffusivity is crucial for understanding material behavior under irradiation and for nuclear reactor safety.
• Existing methods often struggle with the complex microstructures and geometries of irradiated materials.

Purpose of the Study:

• To develop and validate an experimental methodology using photothermal radiometry for accurate bulk thermal diffusivity measurements.
• To adapt the technique for characterizing friable nuclear fuels and materials irradiated to high doses.
• To provide a simplified measurement approach that minimizes uncertainty associated with complex thermal models.

Main Methods:

• Utilized photothermal radiometry (PTR), involving localized laser heating and blackbody radiation monitoring.
• Employed a small interaction volume (<1 mm) to treat sample fragments as a thermal half-space and capture microstructural features.
• Used thermal diffusivity standards representative of fresh and spent nuclear fuels, including a porous microstructure sample.

Main Results:

• Successfully demonstrated the capability of PTR for measuring thermal diffusivity in challenging nuclear materials.
• The methodology circumvents complex thermal wave models, avoiding associated large measurement uncertainties.
• Validated the approach using materials with thermal diffusivities relevant to nuclear fuels and irradiated samples.

Conclusions:

• Photothermal radiometry offers an accurate and robust method for measuring thermal diffusivity in irradiated nuclear materials.
• The simplified approach reduces uncertainty and is applicable to friable, irregularly shaped samples.
• This technique is broadly applicable to various advanced materials, including single crystals and additively manufactured components.