3D imaging of a nuclear reactor using muography measurements with Micromegas detectors.

Transmission muography is a non-invasive and non-destructive imaging method which allows to estimate the integrated density of a volume in a given direction (also referred as opacity). It relies on a reconstruction of muons tracks that crossed the studied volume compared to the corresponding open sky expectation. The experimental setup of the muography developed at CEA Irfu consists in portable muon telescopes. Each of these instruments has four Micromegas gaseous detectors, power and acquisition electronics, and an embedded computer connected to the network allowing remote control. It is then well adapted to deploy them in constrained environments. A muography measurements campaign has been carried out in the decommissioned nuclear reactors G2 and G3 at CEA Marcoule (France) which are expected to be dismantled. We were able to conduct 2D muographies and 3D analyses of inside G2's airtight concrete chamber. In this paper we describe the measurement protocol at the G2 and G3 reactors. We explain what was developed to improve the measurements between G2 and G3 campaigns. It shows how potential improvements were identified in the proof of concept and why we expect a better reconstruction for G3. Among the improvements, we describe how simulations prior to the measurements, denoising and in general automation play an important role to have a precise 3D image in reasonable time. [ABSTRACT FROM AUTHOR]