Speaker
Description
Nuclear power plant generates electricity by nuclear fission reactions, from which Spent Nuclear Fuel (SNF) and radioactive waste are inevitably generated. Since SNF includes 235U, 239Pu, and fission products, the effective management and supervision techniques are necessary for non-proliferation of nuclear materials. The IAEA has conducted Safeguards activities using varying non-destructive analysis techniques for early detection of the misuse of nuclear material. Among the IAEA’s techniques, Gamma Emission Tomography (GET) is one of the most reliable techniques for detecting partial-defects within the SNF. In our previous study, we fabricated the prototype of scintillation crystal-based GET instrument named Yonsei Single-photon Emission Computed Tomography (YSECT), and its performance was evaluated in air using the fresh nuclear fuel. The current study aims to experimentally evaluate the performance of YSECT with the mock-up of SNF and pool (test water tank).
The YSECT instrument consisted of 4 detection modules, and each detection module was composed of the tungsten collimator, 46-channel GAGG scintillation crystals, and silicon multiplier. Data acquisition module (from PETsys Electronics Co. Ltd.), Peltier device-based heat reduction module, and rotating stage were also employed. Moreover, a slip ring was applied to implement the spiral rotation without kink and damage of the cable. The mock-up of SNF was determined as 137Cs P04 capsule from Eckert & Ziegler Co. Ltd. taking into account of the actual SNF in terms of geometry and major gamma-ray energy. Also, the test water tank was fabricated in agreement with the geometry of the prototype YSECT. The prototype YSECT rotated a total of 360° in 5° intervals, and the sinograms were obtained in air and water to assess the degree of attenuation & scatter under different conditions. The quality of each tomographic image was analyzed through spatial resolution and Signal-to-Noise Ratio (SNR).
The spatial resolution of projection images acquired in air and water was analyzed as 10.8 and 14.12 mm, respectively. The SNR of each projection image was calculated to be 8.31 and 5.21, respectively, since the noise level of the projection image obtained underwater increased by a factor of 1.65 due to scattering, as well as the gamma-ray was not sufficiently detected due to attenuation compared to the air condition. To reconstruct the sinogram into the tomographic image, the filtered back-projection with Ram-Lak filter was employed using the MATLAB program. Despite image quality degradation due to high-attenuation and -scatter condition, the SNR of tomographic image acquired underwater was analyzed to be 5.18. In agreement with the rose model, in that the SNR was greater than 5, the source distribution on the tomographic image obtained with the prototype YSECT can be distinguished to the human eye. These results indicated that the developed YSECT can be effectively applied to Safeguards activities to detect partial-defects within SNF.
In the current study, the performance of prototype YSECT was experimentally evaluated with the mock-up of SNF and pool. Based on the results, we believe that the developed instrument can meet the objectives of the IAEA Safeguards activities to prevent proliferation of nuclear material. For further study, a 3-dimensional reconstruction algorithm will be developed to rapidly obtain the full tomographic image of 400 cm long PWR-type SNF.
| Workshop topics | Detector systems |
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