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Zirconium Oxide Thickness Measurement Using FTIR

A non-destructive solution that allows for oxide measurements with minimal worker dose

Zirconium Oxide Thickness Measurement Using Fourier Transform Infrared Spectroscopy (FTIR)

Problem Statement

Samples from nuclear stations can be significantly irradiated and therefore a source of dose for workers during post-service component examinations, especially when metallurgical operations are required.  Increasingly, materials that have been irradiated in the core of CANDU nuclear reactors are being submitted to Kinectrics for analysis. In particular, analysis of oxide thickness of zirconium-based metals has been requested as a means of determining in-core residency times. A non-destructive solution that allows for oxide measurements with minimal worker dose has been developed and demonstrated.

Kinectrics Solution

The Fourier Transform Infrared spectroscopy (FTIR) technique uses an infrared (IR) light source to pass through the sample and onto a detector, which precisely measures the amount of light absorbed by the sample. FTIR analysis provides information on the amount of energy at each frequency that is absorbed by the sample (this corresponds to the frequencies of vibrations between the bonds of atoms). This absorbance creates a unique spectral fingerprint that is used to identify the molecular structure of the sample and to determine the exact quantity of a particular compound in a mixture. 
By conducting FTIR analysis on a controlled series of un-irradiated, Zircaloy-4 samples, previously oxidized in controlled environments, one is able to relate the peaks in the FTIR spectrum to the thickness of the oxide layer. A calibration curve for measurements of oxide thickness using the FTIR technique can then be created for future evaluations of oxide layer thickness on irradiated Zircaloy-4 material.


Scope of Work 

  • Source and procure un-irradiated suitable material (e.g., Zircaloy-4 metal sheet).
  • Set up and execute capsule tests to grow oxide on the samples under controlled conditions.
  • Characterize the oxide layer on the experimental coupons using FTIR.
  • Prepare metallurgical samples of the coupons and measure the oxide layer thickness using metallography and SEM. It is important to collect sufficient data points for the work to be statistically valid.
  • Using the FTIR analysis and the SEM oxide thickness measurements, create a calibration curve correlating these two data sets together.
FTIR spectral results were successfully generated utilizing the oxidized Zircaloy-4 test coupons.  The number of peaks and their positions in a spectrum are uniquely related to the oxide thickness as defined by the interference equation.   
The interference peak order and corresponding peak location, along with the average and standard deviation generated from independent replicates for all the coupons, were then tabulated.  This data was then linked to the metallurgically-obtained oxide thickness measurements.

Using the established relationship for the given metallic substrate, oxide thickness can be estimated for irradiated material samples by measuring the FTIR response.  This process can be established for other materials as well as the current Zircaloy-4 already developed.