Radiological mapping of nuclear facilities under dismantlement drawn up by Digital Autoradiography technique

Abstract

International audienceDigital Autoradiography (DA) is a conventional technique for the detection and quantification of radioactivity, commonly used in molecular biology research. It consists of the exposure of a radiosensitive flexible screen (a few hundred cm$^2$) to $\beta$ sources, such as mice sections with radioactive tracers ( $^3$H, $^{14}$C etc.) in it. After partial ionization, screens are scanned in a dedicated apparatus, which provides a quantitative image of the radioactivity distribution in the sample, in the form of black spots, shadows... Since 2011, this technique has been rerouted from molecular biology research to characterization of nuclear facilities to be dismantled. In this application, floors, walls, ceilings of the facility to investigate are fully or partially covered by batches of screens. After screen scanning and data processing, a radiological mapping of the facility can be obtained, in a reasonable time (roughly a few weeks for areas, often larger than 100 m$^2$); moreover, the implementation of geostatistical tools can dramatically shorten this duration. This approach should systematically be inserted in the range of common methods of contamination detection and quantitation used in dismantlement projects, such as wipe tests, insitu probe counting, and destructive laboratory analyses of samples from the facility. Indeed, DA is quantitative, sensitive to both labile and fixed contamination, and to both penetrating and nonpenetrating radiations ($\alpha$ and low-energy $\beta$, such as $^3$H). Besides, it does not involve nuclear matter transportation, nor does it produce wastes (reusable screens), it requires neither power supply, nor operator presence during acquisition. Thanks to the accurate localization of potential contamination spots, it enables relevant and representative sampling for further destructive laboratory analyses of drilled cores, broken pieces and powders of facility construction material