Simultaneous localization and mapping (SLAM) techniques are widely researched, since they allow the simultaneous creation of a map and the sensors’ pose estimation in an unknown environment. Visual-based SLAM techniques play a significant role in this field, as they are based on a low-cost and small sensor system, which guarantees those advantages compared to other sensor-based SLAM techniques. The literature presents different approaches and methods to implement visual-based SLAM systems. Among this variety of publications, a beginner in this domain may find problems with identifying and analyzing the main algorithms and selecting the most appropriate one according to his or her project constraints. Therefore, we present the three main visual-based SLAM approaches (visual-only, visual-inertial, and RGB-D SLAM), providing a review of the main algorithms of each approach through diagrams and flowcharts, and highlighting the main advantages and disadvantages of each technique. Furthermore, we propose six criteria that ease the SLAM algorithm’s analysis and consider both the software and hardware levels. In addition, we present some major issues and future directions on visual-SLAM field, and provide a general overview of some of the existing benchmark datasets. This work aims to be the first step for those initiating a SLAM project to have a good perspective of SLAM techniques’ main elements and characteristics.

The Timepix3 hybrid-pixel readout chip consists of a matrix made of 256 × 256 square-shaped pixels with a 55 μm-pitch, which can be hybridized to several semiconductors, such as silicon (Si) or cadmium telluride (CdTe) with thicknesses up to 5 mm. Working as an eventbased readout chip, it simultaneously records the Timeover-Threshold (ToT) in each pixel, measuring the deposited energy, as well as the Time-of-Arrival (ToA), with a time resolution of 1.5 ns. In this paper, we present the energy calibration of two Timepix3 chips: the first one was bump-bonded with a 300 μm-thick silicon sensor and the second one with a 1 mm-thick cadmium telluride sensor. Both detectors were calibrated with per pixel calibration, using the monochromatic SOurce of Low-Energy X-rays (SOLEX from LNHB at CEA Saclay) and a set of calibration-grade sealed radioactive sources. Evaluations were carried out over the energy range of 6 keV – 122 keV for Timepix3 Si and 20 keV – 1.332 MeV for Timepix3 CdTe. Based on this experimental procedure, an energy resolution of 2.6 keV (3.4 %) at 59.5 keV was observed for Timepix3 Si. For Timepix3 CdTe, this parameter was 5.6 keV (9.4 %) at 59.5 keV, 27.24 keV (4.1 %) at 661.7 keV, and 47.4 keV (3.5 %) at 1.332 MeV. It is the first time that CdTe bump-bonded Timepix3 spectral performances were evaluated for gamma-rays above 1 MeV. The reconstruction of the full-energy peak for such high energies is possible thanks to the ToA information, which allows the identification of all interactions caused by a given gamma-ray within the detector.

In this article, we aim at measuring a low-activity uranium contamination deposited on concrete surfaces of a nuclear facility and presenting varying enrichment levels. Considering this application field, CEA LIST, has developed an original approach, combining gamma-ray spectrometry based on high-purity germanium (HPGe) measurements and specific Bayesian algorithms. This methodology gives access to an indirect surface activity estimation, assuming that the ratio between the number of alpha particles to be quantified and the number of detected gamma rays is known. The Bayesian approach characteristic property is able to inject a representation of the physical context in the form of a probabilistic a priori. It enables to improve the tradeoff between the true detection rate (TDR) and the false alarm rate (FAR) at low count rates and takes benefit of a richer time-energy information structure than the algorithms used in the conventional detection procedures. The performance evaluation and characterization of Bayesian statistical tests are performed using classical receiver-operating characteristic (ROC) curves by comparison to frequentist hypothesis tests. Results indicate that the Bayesian approach has a superior detection performance for low-activity uranium contamination compared to the frequentist approach. The estimated gain is contained between 30% and 50%, considering a variable or stable radiological background. The Bayesian approach offers the best tradeoff between the TDR, FAR, and the response time and is compatible with the user's requirements.

In recent years, there has been an increase in Dismantling & Decommissioning (D&D) operations of nuclear facilities, driven by the ageing of infrastructures and political decisions to phase out nuclear power. These operations, which can last from a few years to several decades, require mature and reliable techniques that meet international standards, local safety regulations, and radiation protection criteria. Despite developments in robotics, sensors, and digital tools that could reduce manual labor and risk exposure, their deployment remains limited due to financial and logistical constraints. The EU-funded projects CLEANDEM and XS-ABILITY address this challenge by upgrading advanced nuclear sensors and mounting most of them on autonomous terrestrial (CLEANDEM) and both terrestrial and aerial (XS-ABILITY) robots. These robots are and will be designed to assist operators by enabling continuous monitoring during D&D processes, reducing radiation exposure (CLEANDEM), and accessing hard-to-reach areas and difficult to measure radionuclides (XS-ABILITY). They also minimize human errors and organizational issues related to limited intervention time and repetitive tasks. CLEANDEM's results were showcased at its final workshop, and XS-ABILITY, launched October 1^st 2024, will build upon these developments to further improve safety and efficiency in D&D operations. This work focuses on CLEANDEM's technical developments, and presents XS-ABILITY as one of its perspectives.

Human intervention is still required nowadays for most operations conducted during the Dismantling & Decommissioning (D&D) steps, which cover a wide range of radiological conditions: from the harsh initial conditions, nearly identical to when operating, to the final decommissioning steps where radioactivity has been removed. The goal of the three years EU-funded CLEANDEM project, led by CEA List, is to deliver a unique platform which will support the end-users’ operations, from the initial radiological assessment to the final characterization of the facility, while enabling their continuous monitoring during the D&D operations. Ten leading actors from four European countries’ nuclear industry and research, have joined their expertise and efforts in the CLEANDEM consortium to develop a mobile unmanned ground platform (UGV), equipped with upgraded highly-mature detection technologies for 3D-localized radiological measurements. These will complete the facilities’ available data into a 3D and fully detailed Digital Twin of the surveyed area, thus improving the planning and traceability of the D&D operations.

This paper aims to give an overview of very recent European coordinate efforts to implement technologies of the “4.0 Industry” in the nuclear deconstruction sector. This objective aims to benefit from the lever of efficiency and reliability represented by innovative technologies on all the value chain of the dismantling, from early characterization to the dismantling operations themselves through engineering studies, waste management, project management and coordination of multiple stakeholders of each project. The outcomes of five projects (INNO4GRAPH, LD-SAFE, PLEIADES, CLEANDEM and INSIDER) are summarized here. They result in a unique data and knowledge common base, as well as in a significant sharing of experience based on dismantling projects already carried out or to come. They also result in designing new tools or methods natively taking into account the needs of a maximum of dismantling operators, as well as new test facilities. This will allow the undertaken joint work and collaboration to be continued. All of this paves the way to further collaborative projects and developments, in order to continue to implement reliable new technologies and processes in European dismantling projects to make future dismantling operations more efficient, safer and more cost-effective.