This article explores the complex challenges associated with detecting and identifying radioactive hotspots in the nuclear industry using gamma cameras. Gamma cameras facilitate the localization of radioactive hotspots by overlaying a visualization of radioactivity onto a visible image. In the nuclear industry, gamma rays are observed in an energy range spanning from 59.5 keV (Am-241) to 1.3 MeV (Co-60).The motivation for this exploration stems from a specific challenge: characterizing hot-cells inaccessible to human operators. At the ORANO La Hague radioactive waste reprocessing plant, access to these restricted regions is possible through apertures with diameters ranging from 8 to 10 cm. In collaboration, the Nanopix-v1, characterized by its compact form as a coded mask gamma imaging system, with dimensions of 8×5.1×4.3 cm³ and a mass of 268 g, was developed through the synergistic efforts of CEA List and X-ray Imaging Europe (XIE) in partnership with ORANO.This article conducts a detailed examination of the laboratory and in situ performance of the Nanopix-v1, carried out within the challenging operational environment of the La Hague radioactive waste reprocessing plant. The focal point of the article is a comprehensive exploration of the technological components supporting the Nanopix-v1, along with an explanation of the coded mask imaging localization methodologies that underpinned the rigorous evaluation process. The performance of the gamma camera is evaluated through a series of carefully conducted trials, aimed at evaluating the angular resolution and minimum measurement time, including laboratory conditions, experimentation within a metrological Cs-137 irradiator, and practical implementation at the ORANO La Hague site.

In nuclear industry, localizing and visualizing radioactive hot spots is crucial, with applications spanning decommissioning, waste management, radiology in nuclear medicine, and homeland security. Gamma imaging offers a solution for remote localization and visualization of radioactive hot spots. Based on Timepix3 technology, our gamma imaging system is able to deploy two different imaging modalities: coded aperture and Compton imaging. This research introduces a combined approach, referred as multimodal imaging, validated through Monte-Carlo simulations and experiments using a Timepix3 technology coupled with a MURA rank 7 coded aperture. One of the goals of such an imager is to incorporate both techniques’ advantages into a single system while also minimizing their respective drawbacks. Adding multiple sources of information for the localization of radioactive hot spots presents various opportunities to enhance the algorithms used in gamma image reconstruction. Furthermore, the overall system is designed to be portable and compact in order to ease its field use.

. - The radiologic characterization is a very important step in dealing with materials and waste streams generated during operational and decommissioning phases of nuclear installations. Its goal is to determine the waste package radiologic content differenting between materials that can be released from regulatory con-trol and those that require further treatment and conditioning to become a stable waste form suitable for future storage and final disposal, according to its classifica-tion. Characterization is also needed in the pre-disposal stages of radioactive waste management to demonstrate compliance with the waste acceptance criteria of the storage facilities. This work presents the strategies developed and implemented by the MICADO EU project for an in-depth and accurate waste characterization and investigation of the different radioactive waste packages considered. It presents its goals, the methods developed and the technologies used contributing to the improve-ment of the safety. Special emphasis will also be given to complementary approaches highlighting the usability of the technologies and the digitalization and accessibility of the data.

Remote localization of radioactive sources is vital to the nuclear industry and high-energy astrophysics. One widely used method to localize radioactive sources relies on indirect imaging with coded aperture cameras. It involves using a coded aperture collimator called the “coded mask” accompanied by a position-sensitive X/gamma-ray detector with a dedicated deconvolution algorithm. However, a known disadvantage of such cameras is their limited field of view, resulting in a restricted capture area when analyzing complex contaminated scenes or transient astrophysical events. Our paper introduces a new non-planar coded mask prototype designed to expand the field of view of standard coded aperture cameras. Our 3D coded mask is a tantalum hemisphere with a spiral-shaped hole. We use the Maximum Likelihood Expectation Maximization algorithm to reconstruct the radioactive source images. We test our prototype on data acquired with Timepix3 hybrid pixel detector equipped with our mask.

In the framework of its R&D activities to support the metal industry, the Laboratory for Integration of Systems and Technology of CEA Paris-Saclay started studies with the aim of characterizing scrap metal by means of neutron activation analysis. This involves irradiating samples of scrap metal with a pulsed-neutron source in order to determine the copper composition (mainly Cu-65 and Cu-63). In this scope, the use of a LaBr3 detector with an energy resolution of 14.6 keV at 661 keV is hereby investigated to carry out acquisitions during and between the irradiation pulses. As pointed out in literature, the LaBr3 inorganic scintillator might suffer some damage in a neutron-rich environment. Understanding the degradation of the energy resolution of such detector due to a high dose environment is essential to analyse the recorded signal. In this context, the work described in the present paper explores the coherent creation of neutron induced activation products as well as their respective delayed gamma rays in the quite well established LaBr3 inorganic scintillator by the mean of two steps Monte Carlo simulations performed first with the DCHAIN code, and secondly with the PHITS general purpose Monte Carlo particle transport code. Coherence was shown between neutron-induced activation gamma rays and the isotopes created in the crystal, and between the isotopes created and their decay through time. Thus, this study validate the two-step calculation scheme with PHITS and DCHAIN for both the time and energy aspects.

A prototype of gamma imaging system has been developed for the detection of fuel rod deformations, based on the WidePIX hybrid pixel detector, associated with a collimator. The WidePIX detector used in the frame of these developments is made of 2 x 5 Timepix devices hybridized with a 1 mm-thick cadmium telluride semiconductor. A specific collimator was designed, offering the best compromise between mechanical feasibility, cost, signal-to-noise ratio and angular resolution, and making it possible to visualize the fuel rod deformations. In this work, we present the design of the collimator carried out by Monte-Carlo simulation, and experimental results obtained with this prototype on a Cs-137 and Co-60 metrological irradiator.

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.

We report the investigations made on the use of pixelated plastic scintillator (PS) and silicon photomultipliers (SiPMs) array applied to coded aperture gamma-neutron imaging. Specifically, verification of the ability of a multiplexing readout to discriminate and localize neutron interactions was studied. In its intended configuration, the gamma-neutron imager design consists of a coded aperture aligned with a matrix of $12\times12$ PS each coupled to a SiPM. The coded aperture is a rank 7 modified uniformly redundant array (MURA), composed of 1.2 cm of tungsten, with a surface area of 100.4 mm $\times100.4$ mm and placed at 5 cm from the detector. The pixelated PS is composed of polystyrene and standard fluorophores (20 wt% PPO, 0.03 wt% POPOP) loaded with a lithium carboxylate (Li $\alpha $ -valerate), which allows the triple discrimination between thermal neutrons, fast neutrons, and photons. Each pixel of PS has a dimension of 3.6 mm $\times3.6$ mm $\times3.6$ mm and they are separated from each other by 0.6 mm of polytetrafluoroethylene (PTFE). The photonic and electronic readout consists of the ArrayC-30035-144P SiPM from SensL, Cork, Ireland, connected to the diode coupled charge division readout from AiT. First, this neutron imager design was modeled and simulated using the MCNP6 Monte Carlo code. The encoding capability, field of view, and spatial resolution of the neutron imager were therefore evaluated by simulation. Then, we detailed the experimental setups implemented to demonstrate the feasibility of coupling pixelated PS to SiPM to localize radioactive sources and showed the results obtained. Finally, based on this position-sensitive gamma-neutron detector, a gamma-neutron imager was prototyped and tested.

In this work, different Cadmium Telluride (CdTe) sensor configurations are assessed for the usage in a robot assisted portable gamma camera. In the first part, four CdTe sensors, with thickness of 0.45 mm, 1 mm, 2 mm and 3 mm and pixel sizes of 55 mu m and 110 mu m, are investigated regarding their spectroscopic performance. The photon counting detector Timepixl is hereby used. The 3 mm CdTe sensor shows increase in count rate up to a factor of 1.25 compared to a 2 mm CdTe sensor, 1.84 compared to a 1 mm CdTe sensor and up to 2.71 compared to a 0.45 mm CdTe sensor in the case of Cs-137. In the second part, the 3 mm CdTe sensor was implemented in a commercially available gamma camera, the iPIX. The system was integrated in the bomb disposal robot and tested in different scenarios. The integrated 3 mm CdTe detector measured 21.5 counts per second emitting from a Co-60 source with an activity of 2.8 +/- 0.07 Gbq in 20 meters distance in an open environment. The acquisition time was 116 seconds. The angular resolution was sufficient for the user to localize the radioactive isotope inside the test structure.

Since the out-of-pile semi-integral tests performed at Studsvik in 2011 for the NRC [1] and the Halden Loss-Of-Coolant Accident (LOCA) test series IFA-650 [2], a major safety interest has raised for Fuel Fragmentation, Relocation and Dispersal (FFRD) during a LOCA sequence. In addition to the characteristics of the fuel ejected from the rod after the clad failure, the fuel behaviour before the clad failure is still to be investigated, especially its fragmentation and its possible relocation within the rod during the clad ballooning phase. Furthermore, the chronology and the sequencing of these phenomena is of particular interest. For this purpose, the VINON-LOCA program, lying in the framework of a trilateral agreement between EDF, Framatome and CEA, is aimed at performing Out-Of-Pile heating tests on irradiated repressurized fuel rods, reproducing a typical Loss Of Coolant Accident thermal sequence. The VINON-LOCA experimental set-up is located in the so-called VERDON lab of the LECA-STAR hot cell complex. This lab was dedicated to the VERDON-ISTP program [3]. The VINON-LOCA set-up is thus largely instrumented for addressing not only these FFRD topics, but also Fission Gas Release (FGR), combining both online measurement (gamma stations, gamma camera, acoustic sensor, pressure, temperatures, flow meters, microGC…), and preand post-test characterization (gamma scanning, tomography, metrology, fuel fragments weighing and sieving, gas analyses…). An extensive and substantial qualification campaign has been performed to validate the furnace design regarding the desired test conditions, and to qualify the instrumentation. Following some preliminary modelling and calculations, it has included tests on an out-of-cell twin mockup and tests on dummy inactive rods in the hot cell. This allowed achieving successfully the first experimental qualification test of the program end of 2019 on an irradiated UO2 fuel rodlet. A second irradiated experiment is planned with increased instrumentation capabilities, notably a 2D gamma camera for online fuel motion detection.

A prototype of hybrid gamma imager has been developed, based on a single Timpex3 readout chip hybridized with a 1 mm thick cadmium telluride semiconductor. This prototype combines coded-aperture imaging spectrometry and Compton imaging techniques to perform hybrid gamma imaging. It associates and takes advantage of both techniques to locate gamma emitters. The prototype is designed to be portable and compact in order to ease its field use. In this work, we present experimental results obtained with this prototype in coded-aperture imaging spectrometry mode, Compton imaging mode, and hybrid gamma imaging.

This article presents a procedure for optimizing the charge comparison method (CCM) used for pulse shape discrimination (PSD). Without prior knowledge of the signals or the readout system, our procedure automatically optimizes the integration periods maximizing the discrimination ability of the radiation detector. This procedure is innovative in its adaptability and automation without being complicated to implement on a standard computer. Another advantage of this approach is the possibility to use it even if the operation of the readout system and the recording process of the signal is not fully known. Therefore, it enables all detection systems generating signals whose temporal evolution depends on the origin to optimize the integration periods of the CCM. Our procedure is based on verifying that two criteria are met in terms of the number of components and the correlation of Gaussian fits made on the distribution of the tail-to-total integral resulting from the CCM. We tested the procedure for different application cases. First, the optimization of the integration periods of the CCM was performed for the discrimination between fast neutrons and gamma rays with a plastic scintillator and a silicon photomultiplier (SiPM) in the energy range [250 keVee; 4.5 MeVee]. The integration periods, from the laboratory’s experience with photomultiplier tubes (PMTs) and plastic scintillators, gave a Figure of Merit (FoM) of 0.58 corresponding to a rejection ratio (RR) of 8.6%. The procedure improved the FoM up to 0.88 corresponding to a RR of 1.9%. We also applied the procedure to the discrimination between beta and gamma rays with a PMT and a phoswich organic detector and to the discrimination between signals collected from neutrons or partial discharges within a fission chamber.

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 event-based readout chip, it simultaneously records the time-over-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 article, 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 CdTe sensor. Both detectors were calibrated with per pixel calibration, using the monochromatic SOurce of Low-Energy X-rays [SOLEX from Henri Becquerel National Laboratory (LNHB) at CEA Saclay] and a set of calibration-grade sealed radioactive sources. Evaluations were carried out over the energy range 6-122 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 due to the ToA information, which allows the identification of all interactions caused by a given gamma ray within the detector.

Localization of radioactive hot spots is an important issue for nuclear industry (decommissioning, waste management, radiation protection) as well as for Homeland Security applications (non-proliferation of special nuclear material and management of nuclear accidents) or for nuclear research (Gen IV and fusion reactors). Seeking out the fast-neutron emission is of great interest as an alternative to only-gamma imaging techniques. This work presents a highly compact (19x14x15 cm(3), 2.2 kg) fast-neutron imager based on a MURA coded-aperture and a Timepix detector equipped with a specific converter layer. Neutron detection is obtained by adding a conversion layer of paraffin, sensitive to fast neutrons, on the Timepix detector. This semiconductor pixel detector is capable of identifying the charged particles (protons in our case) resulting from the neutron interactions. This paper describes the design and characterization of the main building blocks of our fast-neutron imager. First experimental demonstration of the prototype version will be also presented.

Gamma imaging is a technique that allows the spatial localization of radioactive sources in decommissioning phases of nuclear facilities, nuclear waste management applications, radiation protection, and Homeland Security. One asset of this technique is the possibility to quickly localize radioactive sources associated with a quantitative information on their intensity. Using gamma camera diminishes the dose received by operators and consequently respects the ALARA principle ("As Low As Reasonably Achievable"). For several years, CEA LIST has been designing a coded aperture gamma camera, called GAMPIX. This imager was industrialized by MIRION Technologies (CANBERRA) under the commercial name of iPIX. An extensive study was initiated to validate the GAMPIX quantitative performances for evaluation of dose rate and associated uncertainties. The validation was performed with single and multiple radioactive sources covering an energy range from 60 keV to 1.3 MeV. This article presents experimental results obtained with the GAMPIX gamma camera in the framework of the EMRP ENV54 METRODECOM project.

In the framework of a national funded program for nuclear safety, a first prototype of portable gamma camera was built and tested. It integrates a Caliste-HD CdTe-hybrid detector designed for space X-ray astronomy coupled with a new system-on-chip based acquisition system (FPGA and ARM microprocessor) and thermo-electrical coolers for a use at room temperature. The complete gamma part of the camera fits in a volume of 15×15×40cm3 for a mass lower than 1 kg and a power consumption lower than 10 W. Localization and spectro-identification of radionuclides in a contaminated scene were demonstrated during several test campaigns. A new generation of system is under development taking into account feedback experience from in-situ measurements and integrating a new generation of sensor cost-optimized by industrial applications called Caliste-O. Caliste-O holds a 16×16 pixel detector of 14×14mm2 and 2 mm thick with 8 full-custom front-end IDeF-X HD ASICs. Two prototypes were fabricated and tested. The paper will present the results of in-situ measurements with the first gamma camera, the spectroscopic performance of Caliste-O and the design of the second generation of gamma camera which aims for real time imaging and spectro-identification.

A known disadvantage of the coded aperture imaging approach is its limited field-of-view (FOV), which often results insufficient when analysing complex dismantling scenes such as post-accidental scenarios, where multiple measurements are needed to fully characterize the scene. In order to overcome this limitation, a panoramic coded aperture gamma-camera prototype has been developed. The system is based on a 1 mm thick CdTe detector directly bump-bonded to a Timepix readout chip, developed by the Medipix2 collaboration (256 x 256 pixels, 55 mu m pitch, 14.08 x 14.08 mm(2) sensitive area). A MURA pattern coded aperture is used, allowing for background subtraction without the use of heavy shielding. Such system is then combined with a USB color camera. The output of each measurement is a semi-spherical image covering a FOV of 360 degrees horizontally and 80 degrees vertically, rendered in spherical coordinates (theta, phi). The geometrical shapes of the radiation-emitting objects are preserved by first registering and stitching the optical images captured by the prototype, and applying, subsequently, the same transformations to their corresponding radiation images. Panoramic gamma images generated by using the technique proposed in this paper are described and discussed, along with the main experimental results obtained in laboratories campaigns.

Nuclear instruments such as alpha/beta contamination meter are frequently used in a compensated mode where the contribution of gamma radiation background is compensated by a guard detector. The signal of interest is then the subtraction of counting from both channels. In practice, the noise signal measured by the guard detector is not strictly equal to the noise contribution into the first detector due to anisotropic biases.The random error (under Poisson assumption) is taken into account to build a hypothesis test. The system is also designed to minimize the systematic error but in some cases, this bias could not be completely removed. The measurement system then shows different behavior when the surrounding environment changes exhibiting inopportune false alarms.A method allowing the false alarms to be suppressed is addressed in this study for compensated measurement. An improvement in terms of reliability has been proven. (C) 2016 Elsevier B.V. All rights reserved.