RADWASTE MANAGEMENT | ROBOTICS
V disassembled, with the process controlled through a virtual environment interface, then documented in detail for final storage.
Semi-automated sorting The Virero project focuses on operational waste such as filter cartridges, bag filters or metallic waste. Separating and sorting the waste is based on a multitude of spatially resolved dose rate measurements or spatially resolved gamma spectrometric measurements. Coupling innovative nuclear radiation measurement technology with the industry-proven laser scanning technology in the Virero system results in a reconstruction of all the waste. Since Virero is an ongoing R&D project, the development
is carried out on prototypes of the future system. The final system will be redesigned based on findings from the research project.
Characterising the waste To radiologically characterise waste, the material must be removed from the waste barrel. Several robotic kinematics, sensors and peripheral systems, such as grippers and tools for separation, are integrated into the test facility to handle the waste. Large pieces are cut up with mechanical cutting shears and then spread out with the other waste for radiological characterisation on a measuring table. The kinematic systems used for this purpose are built at FAPS (Figure 1).
Exact object and environment representation is the basis
of robot-based teleoperation. Handling tasks during robotic semi-automated sorting require an exact representation of the environment and the location of waste parts in the working area of the sorting system. An exact representation requires high image quality and
low transmission latency to enable the movable waste parts to be sorted as a digital twin within a virtual reality (VR) environment (Figure 2).
3D laser scan The geometric characterisation of the waste to be sorted is carried out using a 3D line profile scanner with an optical scanning rate of up to 5kHz and a height resolution of approximately 25µm. For a complete recording of the material to be measured, the line scanner moves over the measuring table in several paths, and the recorded height profiles are transferred into a common-point cloud. Laser scanning of each piece of waste takes place
instantaneously, prior to the radiological characterisation. After the laser scanning has been completed, radiological
characterisation begins. The prototype scanning table is shown in Figure 3.
Gamma spectrometry In Virero, radiological characterisation methods are being developed beyond the current state of science and technology. For radiological characterisation, Framatome’s partner
AiNT, is testing the use of three gamma spectrometric detectors of varying sensitivity and a Geiger-Müller counting tube. The gamma spectrometric detectors are a highly sensitive HPGe semiconductor detector (relative photopeak efficiency of 40%), a CeBr3
scintillation detector and a NaI
(Tl) scintillation detector. These detectors are designed for low to medium local dose rates. In contrast to the detectors, the Geiger-Müller counting
tube offers no energy resolution. However, it can be used for LDR values up to 10Sv/h, so that even highly active waste can be characterised. The detectors used are shown in Figure 4. The
Above, figure 1: In the current test facility, receptacles for three 200-litre drums are integrated. With four robot systems, parts can be sorted, cut and observed from different perspectives. For documentation, a stereo camera is mounted on the robot (right) and intuitively controlled by the operator’s viewing direction
radiological measurements are performed in a collimated manner at discrete measurement positions, whereby the radiation signal from individual spatial partitions on the measurement table is measured in each case. Three different collimators can adjust the field of view for each detector. This allows users to vary the size of the partitions to be measured. Hard lead is the collimator material.
2 2 2 2 1 3 1 3
Above, figure 2: Comparison of the real view of the sorting table (left) with the VR model for teleoperation (right). The plant (1) and the Yaskawa robots (2) are integrated in the VR environment as a CAD model. The components to be sorted (3) are reconstructed in VR during runtime using the stereoscopy of the camera mounted on the Stäubli robot
46 | February 2022 |
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Activity reconstruction Teleoperated sorting according to existing radioactivity requires reconstruction of the activity inventories of the waste on the table from spatial and radiological measurement data. Waste components may be contaminated at specific points or over a large area on the surface or their activity may be almost homogeneous (in the case of used filter cartridges, components activated by neutrons such as reactor core internals, etc). To reconstruct the activity, nuclide-specific net pulses
registered in the detector during the measurement are determined from recorded gamma spectra. Photopeak efficiencies are also required, to quantify the likelihood that radiation emitted from a waste piece was detected.
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