EPJ Web Conf.
Volume 253, 2021ANIMMA 2021 – Advancements in Nuclear Instrumentation Measurement Methods and their Applications
|Number of page(s)||7|
|Section||Decommissioning, Dismantling and Remote Handling|
|Published online||19 November 2021|
Localization of nuclear materials in large concrete radioactive waste packages using photofission delayed gamma rays
CEA, DES, IRESNE, DTN, SMTA, Nuclear Measurement Laboratory, F-13108 St Paul-lez-Durance, France
2 CEA, DES, IRESNE, DER, SPESI, Instrumentation Sensors and Dosimetry Laboratory, F-13108 St Paul-lezDurance, France
3 CEA, DES, IRESNE, DTN, F-13108 St Paul-lez-Durance, France
4 ANDRA, French National Radioactive Waste Management Agency, F-92298 Châtenay-Malabry, France
5 Université Grenoble Alpes, CNRS, Grenoble INP, LPSC-IN2P3, 38000 Grenoble, France
* Corresponding author: firstname.lastname@example.org
Published online: 19 November 2021
The characterization of radioactive waste packages is mandatory for their transport, interim storage and final disposal. In this framework, the Nuclear Measurement Laboratory of CEA DES IRESNE Institute, at Cadarache, France, uses a high-energy electron linear accelerator (LINAC) to produce an interrogating bremsstrahlung beam with endpoint energies ranging from 9 to 21 MeV to perform X-ray imaging and high-energy photon interrogation on large concrete packages. In particular, highenergy photon beam induces photofission reactions in both fissile (235U, 239Pu, 241Pu) and fertile (238U, 240Pu, 232Th, etc.) actinides possibly present in the radioactive waste. In order to assess their mass, we use delayed gamma rays emitted by their photofission products, which are measured with a 50 % relative efficiency High-Purity Germanium (HPGe) detector. Actinide differentiation, which is important for the fissile mass estimation, is based on the ratios of gamma rays emitted by different photofission products and requires appropriate corrections for the gamma attenuation in concrete. To this aim, we report here a localization method of point-like nuclear materials in the concrete matrix, based on the differential attenuation of several gamma rays emitted by a same photofission product. We use here the 1435.9 and 2639.6 keV lines of 138Cs, with both experimental data and MCNP numerical simulations to determine the (r,θ) coordinates of nuclear materials. Then, the depth inside the concrete matrix, which is determined with a precision of a few percent, mainly depending on counting statistics on 1435.9 and 2639.6 keV net peak areas, is used to correct for the different gamma ratios used in the actinide identification method. Experimental tests with uranium samples have been performed to validate the localization method.
Key words: Photofission / Uranium / Delayed gamma rays / Bremsstrahlung / MCNP / Concrete matrix / Nuclear material localization
© The Authors, published by EDP Sciences, 2021
This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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