Thermal Properties Measurements of Surrogate Nuclear Fuel Compacts Using the 3-Omega Technique

Levi Gardner

Document Type

Presentation

Journal/Book Title/Conference

USU Student Showcase

Publication Date

4-2014

Faculty Mentor

Heng Ban

Abstract

The 3-omega method has long proven to be a reliable measurement technique for thermal characterization of materials of various geometries, including bulk solids, thin films, and micro to nano-scale suspended wires [1][2].The purpose of this study is to collect accurate thermal properties measurements (thermal conductivity, thermal diffusivity, and specific heat capacity) of cylindrical graphite-matrix surrogate nuclear fuel compacts. It is hypothesized that thermal properties measurements will reflect and further validate past measurements found for this material using other methods [3]. Initial numerical work simulated pure axial heat flow. Numerical findings were supported by a 1-D solution to the heat equation, effectively modeling pure axial heat flow with conditions of radial insulation and volumetric heat generation. This hypothesis and model are tested by feeding an AC electric current of frequency omega through the test sample, creating a temperature fluctuation of frequency 2-omega and consequently a resistance of 2-omega. This change in resistance further leads to a voltage fluctuation of 3-omega that is measured using a lock-in amplifier. The amplitude and phase of this third harmonic voltage are functions of the material_s thermal properties. As a steady-state voltage measurement, the sample_s shape requires specific frequency limits for successful signal measurement. Generic plots of the 3rd harmonic voltage amplitude and phase responses will indicate the frequency limits for thermal conductivity, heat capacity determination, and the conditions needed for thermal diffusivity estimation. This experimentation supports the Department of Energy_s mission of validating thermal properties measurement techniques and thermal characterization data for nuclear materials. Future investigation involves quantifying radiation effects on measurement uncertainty in addition to comparing results from using current and voltage sources in testing. References:
[1] L. Lu, W. Yi, and D. L. Zhang, Rev. Sci. Instrum. 72, 2996 (2001).
[2] C. Dames, G. Chen, Rev. Sci. Instrum. 76, 124902 (2005)
[3] C. Folsom, Effective Thermal Conductivity of Tri-Isotropic Fuel
Compacts, (oai:usudigitalcommons.usu.edu:etd-2453), (2012)

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