Research Ideas and Outcomes :
Research Idea
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Corresponding author: Peter Jansson (peter.jansson@physics.uu.se)
Received: 09 Jul 2021 | Accepted: 21 Sep 2021 | Published: 29 Sep 2021
© 2021 Peter Jansson
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Jansson P (2021) Idea of an experimental technique for quantitative passive gamma emission tomography on irradiated nuclear fuel assemblies. Research Ideas and Outcomes 7: e71320. https://doi.org/10.3897/rio.7.e71320
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An idea is presented in which passive gamma emission tomography of irradiated nuclear fuel is developed to enable quantitative information of the spatial activity distribution of selected isotopes within the fuel rods of the assembly. The idea is based on using well-known calibration sources mounted in the measurement device during measurement. The image reconstruction would include the sources, thereby enable quantification of the activity distribution. Should the idea be proven viable, the outcome would be valuable to the global community dealing with characterisation of nuclear fuel in terms of safety, security, safeguards and fuel development.
tomography, nuclear fuel, passive gamma emission tomography, reconstruction, calibration, GET, PGET, QuantGET, QGET
The tomographic reconstruction measurement techniques used widely in medicine have in the recent decades also found its way into the field of characterisation of irradiated nuclear fuel assemblies, see e.g.
For passive gamma emission tomography applied to nuclear fuel, the images produced in the mathematical reconstruction of the measurement data are usually of a qualitative or relative nature. I.e., images are produced where an image pixel intensity is proportional to the emission rate of a particular gamma energy, or for a range of gamma energies, from the location/area in the fuel assembly corresponding to that pixel.
Recently, it has been identified that quantitative evaluation of the spatial activity distribution of a measured isotope is of interest, so that the image pixel intensity can be used as a direct measure to quantify the activity in the pixel area, e.g. in the unit of Bq/mm3, see
The idea presented here has the potential to enable quantitative tomographic evaluation without the need to know the intrinsic detection efficiencies of the detectors in the tomographic device.
Should the idea be validated and proved to be useful, quantitative evaluation of passive gamma emission tomography would be enabled. Detectors in the device could be replaced, e.g. for maintenance purposes, while still allowing the quantitative evaluation of the spatial activity distribution.
It is here suggested to mount one or more well-known calibration source(s) that emits gamma radiation with an energy distribution that resembles that what is of interest in the tomographic measurement device, either in one or more points somewhere outside, but not too far away from, the fuel assembly or in an extended shape (e.g. cylindrical, square, or hexagonal shape) around the fuel assembly. In some cases it might also be possible to mount calibration sources inside the fuel assembly, i.e. in the tubes for instrumentation and/or reactivity control rods. For example, when the spatial activity distribution of 137Cs is of interest, it is suggested to mount calibration source(s) also based on 137Cs to benefit from similar interaction cross sections and gamma radiation transport properties of the emitted energy.
This idea was inspired by
Using the fact that the known calibration sources can be included in the tomographic image reconstruction, the reconstructed image pixels covering them have intensities that can be ono-to-one mapped to the well know activities in the sources. Correspondingly, the intensities in all the other image pixels can be calibrated to quantitative, i.e. absolute, numbers on the activity contents in those pixels.
There are some identified important challenges with the presented idea; The activity of the calibration source(s) to be mounted might need to be so large that special safety challenges must be solved before they can be used. The mathematical procedures used for tomographic reconstruction might need to be adapted to utilize of the knowledge of the acitivity of the references source(s) in the algorithm. The needed uncertainty of the activity of the calibration source(s) might be prohibitively too small to be cost effective.
The feasibility of the idea presented here, including a study of the limitations posed by the challenges identified above, can be assessed using computer simulation programs developed in, e.g.,