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An assessment of contamination pickup on ground robotic vehicles for nuclear surveying application

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Ground robotic vehicles are often deployed to inspect areas where radioactive floor contamination is a prominent risk. However, the accuracy of detection could be adversely affected by enhanced radiation signal through self-contamination of the robot occurring over the course of the inspection. In this work, it was hypothesised that a six-legged robot could offer advantages over the more conventional ground robotic devices such as wheeled and tracked rovers. To investigate this, experimental contamination testing and computational Monte Carlo simulation techniques (GEANT4) were employed to understand how radioactive contamination pick-up on three different robotic vehicles would affect their detection accuracy. Two robotic vehicles were selected for comparison with the hexapod robot based on their type of locomotion; a wheeled rover and a tracked rover. With the aid of a non-toxic fluorescent tracer dust, the contamination received by the all three vehicles when traversing a contaminated area was initially compared through physical inspection using high definition cameras. The parametric results from these tests where used in the computational study carried out in GEANT4. A cadmium zinc telluride (CZT) detector was simulated at heights ranging from 10 cm to 50 cm above each contaminated vehicle, as if it were mounted on a plinth. Assuming a uniform activity of 60 Bq.cm-2 on all contaminated surfaces, the results suggested that due to the hexapod's small ground-contacting surface area and geometry, radiation detection rates using an uncollimated detector are likely to be overestimated by between only 0.07 - 0.12 %, compared with 3.95 - 8.43 % and 1.75 - 14.53 % for the wheeled and tracked robot alternatives, respectively.
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Journal of Radiological Protection
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An assessment of contamination pickup on ground robotic vehicles for
nuclear surveying application
To cite this article before publication: Antonios Banos et al 2020 J. Radiol. Prot. in press https://doi.org/10.1088/1361-6498/abd074
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An assessment of contamination pickup on ground robotic vehicles for
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nuclear surveying application
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A. Banos
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a, J. Haymana, T. Wallace-Smitha, B. Birdb, B. Lennoxb, T.B. Scott a
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a University of Bristol, Interface Analysis Centre, School of Physics, HH Wills Physics Laboratory, Tyndall Avenue,
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Bristol, BS8 1TL, United Kingdom; e-mail: antonis.banos@bristol.ac.uk
ii
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b University of Manchester, School of Electrical & Electronic Engineering, Manchester, M13 9PL, United Kingdom
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iCorresponding Author
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iiAdditional E-mail of corresponding Author antonisbanos@gmail.com
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1.1 Introduction
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In many industries where toxic materials and wastes are produced, unmanned robotic vehicles are commonly used to
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inspect hazardous areas of plants which would otherwise be risky or impractical for humans to investigate [1, 2]. In the
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nuclear industry, high resolution information regarding the locations and intensities of radioactivity is vital for
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developing safe and cost-effective strategies for clean-up and decommissioning of plants and building structures.
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Assessment and quantification of facilities which contain loose radioactive particulates, often small enough to be
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aerosolised, is both challenging and risky for human workers since the dust material that is suspended within the
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contaminated area, and contain radionuclides, can be physically disturbed by worker activities and result in their
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contamination [3].
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In order to obtain reliable data with regards to radioactive contamination within these areas, the ‘hotspots’ or high
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radiation intensity locations must be initially identified through timely inspections. At a later stage and in order to obtain
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high resolution maps, collimated and directional radiation detection, which requires long exposure times, can be
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employed on the areas of interest. For both actions, a purpose-built unmanned robotic vehicle loaded with the appropriate
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instrumentation becomes a valuable tool since it reduces to minimum the health and safety risk of having humans
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undertaking this task [4]. The extensive use of robotics for nuclear applications has been demonstrated since the 2011
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Fukushima Daichii nuclear accident where the emerging challenge of inspection and determination of radioactivity was
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met with the deployment of a wide variety of unmanned robotic vehicles [5-10]. Of course, working in the immediate
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vicinity of a melted reactor core is about as extreme as it gets. More routine operations would include the
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decommissioning of nuclear power plants, fuel reprocessing facilities, waste repositories and related legacy buildings
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[11]. In these facilities, contrary to nuclear accident sites, the highly active material is expected to be found in site-
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specific locations, with large areas likely to be only lightly contaminated, if contaminated at all. This generates the need
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to produce sensitive detection and characterisation systems capable of finding and reporting areas of elevated radiation
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intensity (versus background) whilst distinguishing between naturally occurring radiation versus gamma-radiation
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originating from human activities.
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For environments where ground contact is not desirable, an unmanned aerial vehicle (UAV) could serve as an ideal
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solution [12-15]. However, for enclosed indoor environments with ‘active’ particulate contamination, the substantial
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downdraught of a typical propeller-powered drone combined with the size and load-carrying capacity ratio make them
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unsuitable for this work. Furthermore, low-activity radiation detection becomes much more difficult when flying due to
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battery constraints and corrections required for altitude, making aerial mapping more suited to outdoor use [15]. Tracked
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rovers [5, 16, 17], wheeled rovers [18, 19], pipe-crawlers [20-22], vertical crawlers [23, 24] and other robotic types [25]
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could be used as ground robotic devices for surveying and gamma radiation inspection. With respect to ground robots,
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the amount of contamination any robotic vehicle shall receive from ground-based particulate matter is highly likely to
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be linked to the surface area of the robot that comes into contact with the floor, as well as the type of motion. A system
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which would not spread contamination to previously uncontaminated areas or become excessively contaminated itself,
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leading to inaccurate radiation readings, would be preferable. In this respect, walking robots, which have minimal area
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contact with the ground, offer an attractive solution for limiting contamination pick-up during surveys and manual
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operations [26, 27]. It was hypothesised that, compared to traditional tracked and wheeled vehicles, a hexapod robotic
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system would become less contaminated during deployment in facilities with floor-based contamination in the form of
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micro-scale radioactive particulates or ‘active’ dust. By minimising the spread of hazardous material and contamination
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pick-up on the device, the quality of the overall characterization of the surveyed environment would significantly
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improve. In this work, we will therefore investigate how contamination pick-up is likely to occur on the various robotic
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devices and understand how it will affect the radiation mapping data of an on-board radiation detector. There is no prior
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literature on conducting such an analysis, and hence this work is both novel but potentially important for informing the
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selection of robot platform used for different nuclear inspections.
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1.2 Experimental methods
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Three robotic systems have been tested in this work, each with a distinctly different method of locomotion. It is important
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to note that for the contamination pick-up experiments the robots were tested largely unmodified. It is suggested that
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integration of equipment such as sensors, detectors, cameras, etc. would not affect our study.
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1.2.1 Wheeled rover
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The wheeled robot used in this work is a four-wheeled remote-control robot, known as a Leo Rover’ which was
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designed by Kell ideas Ltd (Figure 1) [28]. It incorporates a rocker design to improve traction over rough terrain, similar
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to NASA’s Mars rovers [29]. Each wheel is driven by an independent in-hub motor and similarly to the tracked rover,
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the wheels are fixed, and steering is achieved by torque differential between the motors.
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Figure 1: Photographic image showing the four-wheel ‘Leo Rover’ from Kell ideas limited.
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1.2.2 Tracked rover
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Figure 2 displays the tracked rover used for testing which is based on the twin-track differential steering platform from
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Nexus automation Ltd [30]. The unit is custom-modified and includes a light detection and ranging (LiDAR) mapping
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system and a retractable power and control wiring spool. Motors and circuitry are housed within a protective aluminium
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casing.
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Figure 2: Photographic image showing the tracked rover from Nexus automation limited.
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1.2.3 Hexapod robot
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The hexapod is a six-legged robot with an aluminum frame platform and is based on the Phantom AX metal Hexapod
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MK-III designed from Interbotix labs (Figure 3) [31]. This is an off-the-shelf kit that comes as a collaborative effort
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from Next-Gen AX Dynamixel robot servos and the Arbotix-M robocontroller. Locomotion is achieved with 18
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Dynamixel AX-18A electric robot actuators, connected to an onboard computer which is loaded with open source
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software (Phoenix code). Remote control can be wireless or wired and power can be supplied either by lithium-polymer
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batteries or through hardwiring. Rubber ferrules are fitted in the bottom side of each leg of the robot to enhance motion
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stability and protect the robot from ground contamination. Table 1 presents the operational parameters of the three robot
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platforms.
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Table 1: Operational parameters of the three robots.
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Robot platform
Powel supply
Control
mechanism
Locomotion
mechanism
Wheeled rover
11.1V DC, 2A
max current per
wheel (4x servos)
Wireless Control
Rolling (Four
wheels)
Tracked rover
11.1V DC, 1.5A
max current per
servo (2x servos)
Wireless
Commander
Tracked robot
Hexapod robot
11V DC, 2.2A
max current per
servo (18x servos)
Wireless Xbee
Control via PC or
Handheld
Walking (Six-
legged robot)
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Figure 3: Photographic image of the off-the-shelf Phantom AX metal Hexapod MK-III by Interbotix lads. In this image a LIDAR
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and radiation detector are integrated to the robot.
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1.2.4 Contamination tests Experimental procedure
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The main objective of the experimental analysis was to create a simulated environment with floor-based contamination
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and examine/compare the contamination pick-up of the robots after exiting this designated area. To simulate
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contamination in the form of fine radioactive dust, the designated floor area was uniformly covered with a layer of
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fluorescent micro-scale powder. For the simulation, a Romax fluorescent tracking powder from Pestfix pest control
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supplies was used [32].
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A flat (1.2 x 1.2 m) surface was selected for the experimental tests. The surface was sufficiently large to allow the
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robots to complete at least one full 360 ° rotation whilst traversing and before exiting to the clean side. The experimental
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area was sprinkled with fluorescent powder uniformly at a density of ~ 50 g.m-2 using a sieve.
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Before each experimental run each robot was thoroughly cleaned and inspected under UV light with photos being taken
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under visible and UV light from various angles. The robot was then placed immediately adjacent to the designated
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contamination area in order to start the contamination test. Individually, each robot was then piloted in a straight line
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through the designated and into the bounding ‘clean’ zone on the far side. The robot was then turned-off, carefully
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collected from the exit area, and placed on clean laboratory benchtop for inspection. Inspection photos and videos of
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the robot were recorded, consistent with prior inspections of each clean robot to provide a basis for comparison between
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their clean and contaminated states. The experimental process was then repeated a second time (after the robot was
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thoroughly cleaned), but with the robot completing a 360° rotation in the centre of the contaminated space before exiting
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the designated area.
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After exiting the contaminated area, each robot was inspected separately under normal and UV light. High definition
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photographic images were taken under both illumination sources. The imaging data gathered under UV lighting was the
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primary data source for contamination analysis. The contaminated surface area from each robot was calculated and
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related to the overall surface area of the device. These surface area measurements were then used to inform subsequent
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radiation simulations to assess the effect that different amounts of contamination pick-up would have on an on-board
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radiation detector carried by each robot.
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For the validity of the experiment it was assumed that the test area was sufficiently large and any small variations in the
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density of fluorescent dust floor coverage would have a negligible effect on the amount of contamination detected on
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the robots. Negligible effect on the thickness and coverage of the fluorescent dust was also assumed after each
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experimental run. Airborne contamination of robots through active movement of the dust was negligible and did not
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contribute to the detectable contamination.
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1.2.5 Radiation Modelling
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If a robot is carrying a radiation detector for mapping purposes, an accumulation of radioactive contamination onto the
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platform will provide a variable offset to the radiation measurements at a close proximity, thereby decreasing the
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accuracy and reliability of the survey data. To computationally model by how much ‘hot’ contamination pick-up onto
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the different robot platforms could offset detector measurements, GEANT4 was simulations were utilised. Developed
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at CERN to efficiently and precisely model particle interactions within the Large Hadron Collider (LHC) experiment,
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GEANT4 is a freely available tool for simulating the interactions of particles within matter, coupled with a vast library
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of experimental physics data describing electromagnetic, nuclear and kinetic processes [33]. GEANT4 allows a user to
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input geometry, materials and specify particle tracking and interaction detection parameters to produce simulation data.
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By treating volumes as homogenous materials with definable compositions and densities, particles of specific energy
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are tracked where reaction cross sections and probability function sampling is utilised to determine reaction rates. In
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simpler terms, a simulation architecture is set where different objects, detectors and their material and elemental
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compositions are defined. This architecture is then populated with sources where high energy particles are generated
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and emitted with their interactions with matter being tracked and counted based on reaction rates derived from
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experimental data libraries. Data presented in this work were generated using version 10.4 of GEANT4 with all
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additional data files using a repurposed version of the “radioprotection” example model provided with the code.
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A model was generated which consisted of a 1.2 m cube full of air with a 10 mm cube Cadmium zinc telluride (CZT)
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detector at its centre to represent a typical micro-gamma spectrometer detector used on a survey robot. The detector,
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designed from Kromek, has an operating energy range of 30 keV to 3 MeV with maximum throughput of 30,000 counts
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per second. Radioactive contamination was modelled for each robot type as a series of distributed surface sources
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approximating the track, wheel or footpad dimensions of the different robots. Detector hits were measured as any particle
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which deposited energy into the CZT bulk, as would be measured by current pulses in the actual detector circuit.
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1.3 Results
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1.3.1 Contamination tests
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1.3.1.1 Wheeled rover
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Figures 4a-f show images from the wheeled robot contamination tests. From traversing the test area, the rover picked
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up significant contamination on the four wheels (Figure 4a-c), with an amount of contamination deposited from the
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robot wheels onto the floor of the adjacent clean area on the exit side (Figure 4b). Negligible contamination was observed
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on the main body of the robot at this stage. After the robot was cleaned, a second trial was carried out with the rover
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completing a full rotation in the centre of the test area (Figures 4d & e). A visibly larger disruption of the contaminated
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floor area was observed (Figure 4d) with a commensurately increased amount of contamination was observed on the
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robot wheels and spread (from the wheels) into the adjacent clean area. Contamination was, again, observed almost
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exclusively in the four wheels of the robot, though comparison of images between the test runs (Figures 4c & e), indicates
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that contamination on the wheels was higher in the second trial (full rotation).
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(a)
(b)
(c)
(d)
(e)
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Figure 4: Images showing on (a) the wheeled rover traversing the test area; (b) the markings left on the exit side of the
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designated environment after trial one (traversing); (c) the contamination picked up on the body of the robot after
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completing trial one (traversing); (d) the tracking marks of the robot within the test environment after trial two (full
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rotation) and (e) the contamination picked up on the body of the robot after trial two (full rotation).
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1.3.1.2 Tracked rover
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Figures 5a-f show images from the tracked vehicle tests. After a simple straight-line traverse of the test area, significant
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contamination coverage was observed on the two tracks of the robot (Figures 5a & b) with smaller amounts of
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contamination spread onto the main body of the robot from the movement of the tracks. Larger accumulations of the
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fluorescent particulate had also become trapped between the track and the tread of the robot. Following the full rotation
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test, a clear area of contaminant disruption in centre of the ‘hot’ area was observed with an accompanying trail of ground
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contamination out into the (initially) clean exit area (Figure 5c). Such contamination trails were observed for both tests
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(traversing and full rotation). Robot track contamination and contamination spread onto the body of the robot was more
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pronounced after a full rotation when compared to a simple straight-line traverse across the test area (Figures 5b & d).
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Figure 5: Images showing on (a) the tracked rover traversing the test area; (b) the contamination picked up on the body of the
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tracked robot after trial one (traversing); (c) the markings left on the exit side of the designated environment after trial two (full
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rotation) and (d) the contamination picked up on the body of the robot after trial two (full rotation).
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1.3.1.3 Hexapod robot
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Figures 6a-e show results from the contamination tests using the hexapod robotic system. After traversing the test area,
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the robot exhibited localised particulate contamination on the rubber ‘foot’ ferrules fitted on the basal tip of the legs
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(Figures 6a-c). Small amounts of spot contamination could be observed on the lowermost 10 mm of the hexapod legs.
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(a)
(c)
(d)
(b)
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From the two tests, both resulted in a contamination trail on the exit side of the ‘hot’ zone, exhibiting a rapidly
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diminished abundance with increased distance (Figure 6a). After completing a full rotation within the contaminated area
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(trial two), some lighter contamination in the lower tibia/leg section was observed, extending to ~ 50 mm from the tip
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of each leg (Figure 6d). Sparse, isolated particulates were also observed on parts of the underside of the vehicle. Minimal
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disruption of the contaminated floor area was observed (Figures 6c), although the elongated shape of the footprints
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recorded in the contamination trails indicated that some slippage of around 0.5 to 1.0 cm has occurred as the robot
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moved. Figures 6b & e show that contamination pick-up on the legs and ensuing contamination of the adjacent clean
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area were increased in the second trial where a full rotation of the robot was executed.
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Figure 6: Images showing on (a) the markings left on the exit side of the designated environment after trial one (traversing); (b) the
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contamination picked up on the rubber ferrule at the tip of the leg after trial one (traversing); (c) the tracking marks of the hexapod
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robot within the designated area after trial one (traversing); (d) the contamination around the tibia section of the robot leg after
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trial two (full rotation) and (e) the contamination picked up on the rubber ferrule at the tip of the leg after trial two (full rotation).
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1.3.2 Contaminated surface area measurement vs radioactivity
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The dimensions and the approximated surface areas were calculated for the floor-contacting components of each robot.
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This was then cross-referenced with the observed coverage of fluorescent dust for each robot. To determine the
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simulated accumulated radioactivity of each robot, based on their observed contaminated area, it was assumed that the
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traction surfaces were perfectly flat, i.e. ignoring tread, patterns, etc. This could lead to either underestimation or
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overestimation of contamination, given that the tread grooves could be covered with dust or be completely clean.
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However, given the significant difference in surface area between the robotic platforms, the comparisons would still be
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valid. It was also assumed that contaminated traction-surfaces of the robots had a uniform coating of material. In reality,
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the amount of contamination would be directly proportional to the thickness and composition of the dust, the pressure
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exerted by the vehicle and the environmental conditions such as humidity, temperature, etc. Still, the single layer
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contamination approach was considered a reasonable approximation for the purposes of this work. Table 2 presents the
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(d)
(e)
(c)
(a)
(b)
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results from this process. The hexapod and wheeled rover yielded a comparable total surface area which was twice that
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of the tracked rover. However, the contaminated surface area for the hexapod robot was considerably lower in
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comparison to the other systems (Table 2). By assigning an arbitrary radioactivity of 60 kBq.cm-2 arising from floor
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contamination, the overall faux radioactivity which was picked up by each robot could be calculated. The results clearly
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indicated that, with the same level of radioactivity per unit area of contamination, the hexapod exhibits an overall activity
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which is 56 and 63 times lower than the wheeled and tracked rovers, respectively.
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Table 2: Integrating some of the calculated parameters for each robot after the contamination pick-up tests.
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Hexapod
Wheeled rover
Tracked rover
Length (cm)
41
41
31
Width (cm)
44
46
30
Overall surface area (cm2)
1804
1886
930
Contaminated surface area (cm2)
9.4
530.9
596.5
Total activity (KBq)
0.56
31.85
35.79
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1.3.3 GEANT4 modelling
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A visualisation of the source distribution chosen to represent the contamination of the floor area as well as that of each
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robot is shown in Figures 7-10. In each visualisation, the red particle traces represent energetic electrons produced by
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the gamma radiation ionising the air within the room. The models of Figures 7-10 were run with 10 million gamma
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particles and 12 repeat runs for each data point with different random seed and by adjusting the distance between the
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source and detector by 5 cm increments. The results of these simulations were presented in Figure 11. The value for
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detector hits per second was adjusted for the total amount of contamination you would expect on each robot type shown
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in Table 2. The results show the detector hits per second you would expect for homogenous 60 kBq.cm-2 contamination
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on the robots and floor.
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Figure 7: Floor contamination source distribution with the distance between the source and cadmium zinc telluride (CZT) detector
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set at 30 cm distance. The simulation was run with 10 million gamma particles.
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Figure 8: Wheeled robot source distribution with the distance between the source and cadmium zinc telluride (CZT) detector set at
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30 cm distance. The simulation was run with 10 million gamma particles.
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Figure 9: Tracked rover source distribution with the distance between the source and cadmium zinc telluride (CZT) detector set at
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30 cm distance. The simulation was run with 10 million gamma particles.
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Figure 10: Hexapod robot source distribution with the distance between the source and cadmium zinc telluride (CZT) detector set
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at 30 cm distance. The simulation was run with 10 million gamma particles.
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From Figure 11 it can be observed that the majority of detector hits would come from the surrounding floor, the
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contamination level of which is homogenous. The tracked rover produced a higher signal than that of the wheeled rover
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but dropped off more quickly with increased detector distance. This was due to the dimensions of the tracked rover
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having a higher distribution of activity at the top and bottom of the tracks, whereas the wheeled rover approximated
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more closely to four point-sources. The hexapod exhibited by far the lowest detector hits by comparison, meaning that
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during a gamma detection measurement in a contaminated plant area the influence on the detector signal due to the
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robot’s self-contamination would be minimal.
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Figure 11: Detector height vs detector hits per second for various active areas of contamination at 60 kBq/cm2 Co60; floor (blue),
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wheeled rover (yellow), caterpillar track rover (orange) and hexapod (grey).
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For all the simulated sources of gamma radiation; floor, hexapod, tracked and wheeled, the relationship between the
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number of gamma hits on the CZT detector crystal and its distance above the ground surface (representing different
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mounting heights above the robot chassis) could be described by an exponential in the form of Equation 1:
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   , (1)
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with “yin hits per second for 60 kBq/cm2 contamination over each surface type. “Ais the value for hits at x = 0 or
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where there was no distance between the detector and the source (as exp(0) = 1), “Bwas the gradient with which the
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number of detector hits per second decays with increased simulated detector height, as seen in Figure 11. In order to
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calculate the error caused by each robot type, E, the following equation was used:
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   
 (2)
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where i is the added erroneous gamma hits influencing the detection measurement of F. The error, E, was therefore
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calculated as a percentage of the measurement of F. To find a general error equation for a decaying exponent, both i and
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1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
1.0E+02
0 10 20 30 40 50 60
Detector Hits /s
Detector Height /cm
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F could be substituted with their respective decay equations derived from Figure 11. Where Ai was the tracked, wheeled
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and hexapod equations whilst F was the line fitted to the floor contamination measurements. Dividing the two
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exponentials gives Equation 3 as:
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   
(3)
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Therefore, the associated error induced by self-contamination on each robot type can be expressed by the following
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equations:
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
, (4)
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
, (5)
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
 , (6)
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where E% is the percentage error in the detection measurement due to the accumulated contamination on the robot and
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x is the elevation of the detector above the floor, mounted at different heights on top of the robot. These equations were
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derived from the fitted exponentials for each robot type shown in Figure 11. This showed that at x = 10 cm, the signal
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from the tracked and wheel robots was 119 and 69 times larger, respectively, than that of the hexapod. The first
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coefficient in Equations 4-6 are characteristic of the dimensions of the robots and their contaminated surfaces, so the
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small traction-surface area presented by the hexapod’s feet significantly reduced this coefficient and hence reduced the
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associated erroneous gamma counts that would register on the detector from the accumulated self-contamination. The
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second coefficient in the equation’s exponent relates to how the intensity of the measured gamma flux on the detector
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dropped away as it became increasingly elevated above the ground surface; a typical geometrical dilution. These
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equations could be used to appraise the expected ‘contamination performance’ of different robot platforms planned for
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radiation mapping deployments and also to calculate an offset correction to radiation survey measurements where
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radioactive contamination of a robot is considered to have occurred.
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1.4 Discussion
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Robotic vehicle contamination from floor-based radioactive particulates was investigated in this work. To our
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knowledge, this is the first time that such a study has been conducted to compare contamination pick-up between
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different robotic systems. By using fluorescent powder as a surrogate to radioactive dust, contamination pick-pup
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performance could be effectively documented, yielding semi-quantitative results. By comparing the performance of the
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three robots in trial one (straight-line traversing) it was found that the wheeled and tracked robot contaminated their
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traction surfaces almost completely after the first revolution of the wheels or tracks. Only minimal further increase in
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robot contamination was observed as the robots advanced. Similar to the rovers, the hexapod was expected to be fully
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contaminated in the leg area within the first few steps. In all cases the robots were quick to accumulate contamination.
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Performing a full rotation (trial two) resulted in increased disruption of the contaminated floor area and increased
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particulate pick-up onto the tread of both the tracked and wheeled platforms. There was also a commensurate increase
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in the amount of contamination trailed out of the test area. By comparison, the hexapod exhibited no significant
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differences in floor disturbance and contamination trailing between the two experiments. This was ascribed to the
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rotational manoeuvre causing ostensibly only the same disturbance as if it were walking in a straight line. Only a small
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increase in contamination was observed around the tibia section of the legs, which was considered negligible when
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compared to the other robots.
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Upon close inspection, all robots in all experiments had a small amount of particulate speckling to areas other than just
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the traction surfaces, typically on the underside surfaces. The fluorescent dust had a low density (~1.5 g.cm-3) and could
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mobilize into the air from the floor even after small amounts of disturbance. This is considered to be closely analogous
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to micro-scale particulates found in some nuclear facilities [34], although the density of nuclear particulates would be
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expectantly higher but with comparable electrostatic properties.
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The very small amounts of leg and chassis contamination observed on the robots was determined to contribute very little
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to the total overall area of contamination for each platform and, hence, could be ignored for the purposes of radiation
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modelling. Contamination was primarily confined to traction surfaces.
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From Table 2, the overall contaminated surface area of the hexapod robot is considerably lower in comparison to the
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wheeled and tracked rovers. The difference in the total contaminated surface area between the hexapod and the other
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robots could be even higher if we consider that the gait mode used for the hexapod was a single leg mode where one leg
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is advancing at a time. Though this mode is considered safer for hexapod robots as it maintains the maximum number
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of legs in contact with the ground at any one time, it will also represent the gait mode with the worst contamination
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pick-up performance. Additionally, a relatively high speed of motion was used for the hexapod manoeuvres, thus
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creating a larger disturbance of the contaminated floor area. It would be possible to further reduce the contamination
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pick-up by adopting a slow, three-legged gait mode while covering twice the distance per complete movement cycle.
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Whilst the total amount of contamination accumulated by a robot during a deployment is the primary consideration, the
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ease with which a robot can be decontaminated post-mission and later returned to service, is also of significant
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importance. The mobility design of the robots tested in this work was very different and, therefore, cleaning methods
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needed to be adapted for each system. For the wheeled and tracked systems, whilst smooth metal surfaces were easy to
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clean, any contamination in the tyre and track treads was difficult to completely remove. For real-world nuclear facilities
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this might mean that the robots would only be deployed once before being consigned as secondary nuclear waste objects.
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For the hexapod robot, replacement of the rubber ferrules on the legs enabled rapid and almost total removal of the
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contamination. Residual contamination on leg surfaces could be cleaned with relative ease, though some isolated
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particulates infiltrated and contaminated the inner parts of the hexapod’s open-frame leg design. Clean-up of these
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surfaces would require parts of the robot to be disassembled which is highly impractical and time-consuming. It is
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recommended that such contamination could be mitigated by covering the hexapod with a protective sacrificial suit,
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which could be removed and disposed of after each deployment. Such a sustainable approach is not achievable with the
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other two types of robots but would represent a significant operational cost reduction if the system was reused over
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multiple facility deployments.
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One significant advantage of the wheeled and tracked robots is that their resting positions do not change between being
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switched on or off. This means that scheduled or accidental robot power shutdowns will not lead to further contamination
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of the robot from the ground. This is not the case for the hexapod robot which is programmed to rest on the ‘belly’ face
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of the platform when power is switched off. Power shutdowns on the hexapod could be caused after a servo failure if
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the robot carries significant load or is operating within a deployment environment for a long period. To avoid excessive
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underside contamination during a power shutdown event four 30 mm long, 6 mm diameter poles were fitted to the
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underside of the robot to act as resting points. In this way, if the robot was mounted with a pan-tilt scanned on its top
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surface, it could navigate to a strategic location and the power off its leg servos for the duration of the scan without
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accumulating any significant contamination. These four additional points of contact are only discussed as an additional
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contamination safety measure and were not considered in this work. Potential addition of these points would contribute
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a relatively small surface area of contamination and would not affect our results significantly.
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In this study the calculation of the total accumulated gamma activity for each contaminated vehicle was based on an
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arbitrary surface coating value of 60 kBq.cm-2, (Table 2). From Table 2, it is clear that the hexapod robotic system
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accumulated the least radioactivity with the wheeled and tracked robot yielding comparable values. This provides a
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technical underpinning for the consideration that walking robots provide the optimal survey platform for radiation
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surveillance and mapping missions inside nuclear facilities, with quadrupeds representing an improved configuration
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over hexapods, and hexapods being preferable to octopods, and so on.
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Using GEANT4 we were able to investigate the effects that accumulated robot radioactivity could have on a radiation
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detection instrument mounted on the top of each robot. The uncollimated 10 cm3 volume CZT detector simulated in this
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work, represents a common type of micro gamma spectrometer used in survey applications. The modelling study clearly
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indicated that lower amounts of robot-accumulated radioactivity led to detector readings that would be closer to the
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actual radioactivity for a particular area i.e. the true radioactivity level. As the amount of contamination on the robots
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increased, this additional radioactivity located close to the detector added an increasing additional offset to the detector
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reading and, thus, a significant reduction in the accuracy of the measurements. A radiation detector mounted on a
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contaminated robot would provide an overestimate of the true local gamma radiation and this would need to be corrected
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for in post-deployment data processing. The study showed that a way to mitigate this effect would be to raise the height
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of the detector, as much as practicably possible, away from the floor and away from the gamma-contaminated surfaces
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of the robot. This could lead to stability issues depending on the platform and the size and weight of the detector being
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used. Further simulation work could be performed by including other metallic components in each robot platform such
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as metallic casings, sensors, cameras, etc. as they will scatter high energy gammas and produce secondary photons
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which may also affect the detector measurements. Additionally, different types of floor surfaces could be simulated in
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order to assess how backscatter of contamination might affect the gamma detection results in general.
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The GEANT4 modelling also indicated that the footpad design of walking robots could be minimised to limit
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contamination pick-up, with needle-like pads representing the smallest possible ground contact area. Accordingly, either
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a quadruped or hexapod design would represent optimal designs, with the former offering the least ground contact and
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lower power consumption, but with the hexapod offering greater stability and manoeuvrability.
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This study has also highlighted that robotic survey platforms can redistribute particulate contamination during a survey
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mission. A robot traversing a radioactively contaminated area back into a clean one will bring with it some degree of
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contamination. This highlights the need for adaptive path planning on the robotic system, when deployed autonomously,
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to attempt to avoid highly radioactive zones within the survey area to minimise through-mission contamination. These
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radioactive hot zones would be targeted for mapping at the end of the survey once the lower activity zones had been
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delineated. It is also a consideration that any tethers applied to the robotic system, either for physical recovery or data
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transfer, would also provide a route for spreading and redistributing substantial contamination.
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Future work will seek to develop and validate sacrificial skins and coverings for walking robot platforms, examining
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the play-off between enhanced contamination protection versus reduced system heat-loss. Much like human nuclear
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workers, strenuous activity inside a sealed protective suit might expectedly lead to overheating. This is a challenge that
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will need to be overcome if a sustainable, reusable deployment solution is to be made available to the industry.
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1.5 Conclusions
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The extent of contamination pick-up of three different robotic vehicles (wheeled rover, tracked rover and hexapod)
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operating within a floor-contaminated environment was investigated in this work. The differences in accumulated
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contamination between robots was determined using fluorescent micro-scale dust as a surrogate for real nuclear
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particulates. The hexapod robotic system was proven to accumulate and spread significantly less contamination than the
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tracked and wheeled platforms.
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From the GEANT4 modelling, it was demonstrated that the differences in the accumulated contamination between
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platforms would equate to significant differences in the amount of radiation detected by an on-board sensor. The wheeled
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and tracked robots exhibited a comparable performance which could lead to significant over-estimation of the true local-
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area radiation intensity during a survey. By comparison, the hexapod robot exhibited significantly lower detector offset
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due to its propensity to accumulate very little radioactive contamination.
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By taking a control measurement of detector count intensity in a “clean” area with minimal gamma signal, and then
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repeating the measurement after an active deployment, the extent of robot contamination could be determined and an
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offset to any survey results could be applied on the assumption that contamination occurred at the start of the deployment
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and remained approximately constant throughout the deployment.
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This study provides substantial evidence that for robotic survey applications where the ground or surrounding surfaces
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are contaminated with a hazardous particulate material, a walking robot will provide the best performance for
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minimising the amount material pick-up. Such platforms therefore present the best technical option for post-mission
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decontamination and reuse.
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1.6 Acknowledgements
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We would like to acknowledge and thank UK Research and Innovation (UKRI) and its Engineering and Physical
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Sciences Research Council (EPSRC) for funding our research via both the National Centre for Nuclear Robotics
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(NCNR) and Robotics and AI in Nuclear (RAIN) extreme environment robotics research hubs. We would also like to
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thank the Royal Academy of Engineering for fiscal support through their Research Fellowship Scheme and the UK
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Atomic Weapons Establishment (AWE) for their expertise and collaboration in developing the theoretical framework
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of the project.
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1.7 Conflict of interest
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Authors have no conflict of interest relevant to this article.
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1.8 References
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[1] K.A. Kas, G.K. Johnson, Using unmanned aerial vehicles and robotics in hazardous locations safely, Process safety
Progress 39 (2020) e12066.
[2] H. Miura, A. Watanabe, M. Okugawa, T. Miura, T. Koganeya, Plant inspection by using a ground vehicle and an
aerial robot: lessons learned from plant disaster prevention challenge in world robot summit 2018, Advanced Robotics
34 (2020) 104-118.
[3] K.G. Andersson, C. Fogh, M. Byrne, J. Roed, A. Goddard, S. Hotchkiss, Radiation dose implications of airborne
contaminant deposition to humans, Health Physics 82 (2002) 226-232.
[4] R. Pavlovsky, A. Haefner, T. Joshi, V. Negut, K. McManus, E. Suzuki, R. Barnowski, K. Vetter, 3-D radiation
mapping in real-time with the localization and mapping platform LAMP from unmanned aerial systems and man-
portable configurations, arXiv preprint arXiv:1901.05038 (2018).
[5] I. Tsitsimpelis, C.J. Taylor, B. Lennox, M.J. Joyce, A review of ground-based robotic systems for the characterization
of nuclear environments, Progress in Nuclear Energy 111 (2019) 109-124.
[6] S. Kawatsuma, M. Fukushima, T. Okada, Emergency response by robots to Fukushima‐Daiichi accident: summary
and lessons learned, Industrial Robot: An International Journal (2012).
[7] K. Ohno, S. Kawatsuma, T. Okada, E. Takeuchi, K. Higashi, S. Tadokoro, Robotic control vehicle for measuring
radiation in Fukushima Daiichi Nuclear Power Plant, 2011 IEEE International Symposium on Safety, Security, and
Rescue Robotics, IEEE (2011) pp. 38-43.
[8] K. Nagatani, S. Kiribayashi, Y. Okada, K. Otake, K. Yoshida, S. Tadokoro, T. Nishimura, T. Yoshida, E. Koyanagi,
M. Fukushima, Emergency response to the nuclear accident at the Fukushima Daiichi Nuclear Power Plants using
mobile rescue robots Journal of Field Robotics 30 (2013) 44-63.
[9] T. Yoshida, K. Nagatani, S. Tadokoro, T. Nishimura, E. Koyanagi, Improvements to the rescue robot quince toward
future indoor surveillance missions in the Fukushima Daiichi nuclear power plant, Field and Service Robotics, Springer
(2014) pp. 19-32.
[10] M. Sugisaka, Working robots for nuclear power plant desasters, 5th IEEE international conference on digital
ecosystems and technologies (IEEE DEST 2011), IEEE (2011) pp. 358-361.
[11] M.M. Osterhout, Decontamination and decommissioning of nuclear facilities, Springer Science & Business Media
(2012).
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[12] J. Nikolic, M. Burri, J. Rehder, S. Leutenegger, C. Huerzeler, R. Siegwart, A UAV system for inspection of
industrial facilities, 2013 IEEE Aerospace Conference, IEEE (2013) pp. 1-8.
[13] P.G. Martin, J. Moore, J.S. Fardoulis, O.D. Payton, T.B. Scott, Radiological assessment on interest areas on the
sellafield nuclear site via unmanned aerial vehicle, Remote Sensing 8 (2016) 913.
[14] S. Jordan, J. Moore, S. Hovet, J. Box, J. Perry, K. Kirsche, D. Lewis, Z.T.H. Tse, State-of-the-art technologies for
UAV inspections, IET Radar, Sonar & Navigation 12 (2018) 151-164.
[15] D. Connor, P. Martin, T. Scott, Airborne radiation mapping: overview and application of current and future aerial
systems, International Journal of Remote Sensing 37 (2016) 5953-5987.
[16] B. Bird, A. Griffiths, H. Martin, E. Codres, J. Jones, A. Stancu, B. Lennox, S. Watson, X. Poteau, A Robot to
Monitor Nuclear Facilities: Using Autonomous Radiation-Monitoring Assistance to Reduce Risk and Cost, IEEE
Robotics & Automation Magazine 26 (2018) 35-43.
[17] N. Cabrol, G. Chong‐Diaz, C. Stoker, V. Gulick, R. Landheim, P. Lee, T. Roush, A. Zent, C.H. Lameli, A.J. Iglesia,
Nomad rover field experiment, Atacama Desert, Chile: 1. Science results overview, Journal of Geophysical Research:
Planets 106 (2001) 7785-7806.
[18] R.B. Anderson, Development of mobile platform for inventory and inspection applications in nuclear environments,
2015.
[19] A.D. Oliveira, G. Silva, A.R.G. da Silva, R.G. Lins, Proposal of an Autonomous System for Inspection of
Structures, WIEFP20184th Workshop on Innovative Engineering for Fluid Power, November 28-30, Sao Paulo,
Brazil, Linköping University Electronic Press, 2018, pp. 1-4.
[20] A. Shukla, H. Karki, Application of robotics in offshore oil and gas industryA review Part II, Robotics and
Autonomous Systems 75 (2016) 508-524.
[21] A. Shukla, H. Karki, Application of robotics in onshore oil and gas industryA review Part I, Robotics and
Autonomous Systems 75 (2016) 490-507.
[22] A. Nayak, S. Pradhan, Design of a new in-pipe inspection robot, Procedia Engineering 97 (2014) 2081-2091
[23] M. Guimaraes, J. Lindberg, Remote controlled vehicle for inspection of vertical concrete structures, Proceedings
of the 2014 3rd International Conference on Applied Robotics for the Power Industry, IEEE 2014 pp. 1-6.
[24] G. La Rosa, M. Messina, G. Muscato, R. Sinatra, A low-cost lightweight climbing robot for the inspection of
vertical surfaces, Mechatronics 12 (2002) 71-96.
[25] R. Voyles, P. Abbaraju, H. Choset, A. Ansari, Novel Serpentine Robot Combinations for Inspection in Hard-to-
Reach Areas of Damaged or Decommissioned Structures-17335, Proceedings, Waste Management Conference
(WM2017), 2017.
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[26] H.G. Meyer, D. Klimeck, J. Paskarbeit, U. Rückert, M. Egelhaaf, M. Porrmann, A. Schneider, Resource-efficient
bio-inspired visual processing on the hexapod walking robot HECTOR, Plos One 15 (2020) e0230620.
[27] J. Dupeyroux, J.R. Serres, S. Viollet, AntBot: A six-legged walking robot able to home like desert ants in outdoor
environments, Science Robotics 4 (2019).
[28] Kell Ideas Limited, Leo Rover (2019), <https://www.leorover.tech/>.
[29] K. Iagnemma, S. Dubowsky, Traction control of wheeled robotic vehicles in rough terrain with application to
planetary rovers, The international Journal of Robotics Research 23 (2004) 1029-1040.
[30] Nexus Automation Limited, <https://nexus18.en.ecput.com/>.
[31] Trossen Robotics, PhantomX AX Metal Hexapod Mark III Kit, Chicago, IL,<
https://www.trossenrobotics.com/phantomx-ax-hexapod.aspx>.
[32] P.P.C. Supplies, Rodent control/ Rodent tracking - Fluorescent Rodent Tracking Dust, <
https://www.pestfix.co.uk/fluorescent-rodent-tracking-dust.asp>.
[33] M. Zarifi, S. Guatelli, Y. Qi, D. Bolst, D. Prokopovich, A. Rosenfeld, Characterization of prompt gamma rays for
in-vivo range verification in hadron therapy: A Geant4 simulation study, Journal of Physics: Conference Series 1154
(2019) 012-030.
[34] W. Jones, Atomic Weapons Establishment (AWE), Personal communication, (2019).
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... Banos et. al [18] conducted contamination pick-up tests by passing three types of robotic systems: a tracked rover, a wheeled rover and a six-legged robot through a benchmarked surface covered with a uniform layer of fluorescent dust, which acted as a surrogate for floor contamination. The test demonstrated that the contaminated contact surface on the first two robots (tracked and wheeled rover) was considerably higher in comparison to the legged robotic system and could substantially invalidate the results of radiation mapping surveys. ...
... The test demonstrated that the contaminated contact surface on the first two robots (tracked and wheeled rover) was considerably higher in comparison to the legged robotic system and could substantially invalidate the results of radiation mapping surveys. [18] The interest in legged insect-like robots for various inspection applications has been boosted in recent years stemming from their remarkable behavioral performance in various aspects such as ease in navigation [19], [20], speed, robustness, energy efficiency [21], and climbing capability [22]. ...
... For the operation phase, the authors further implemented obstacle avoidance capabilities as well as a Dry Chemical Powder (DCP) cartridge fire extinguisher mechanism. Menon et al. [7] developed a solar-powered, autonomous monitoring rover for various agriculture-related tasks such as soil and weather parameter monitoring, fire detection, insect and pest infestation detection, etc. Banos et al. [8] conducted a comparative test between three robotic platforms namely wheeled, tracked, and hexapod, and found out that hexapod robotic platforms performed significantly better in terms of picking up and spreading lesser radioactive contamination during operation. Similarly, Bird et al. [9] developed Continuous Autonomous Radiation-Monitoring Assistance (CARMA) robot. ...
... The rover recognized and located a fixed α source embedded in the floor when the authors deployed it in a radiation active area. The findings of these studies [5], [6], [8], [9] show that human assistant rovers can be useful to replace or assist humans in risky environments. National Aeronautics and Space Administration (NASA) intends to bring Mars under human exploration mission reach within the 2030s [10]. ...
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Human-assistance rovers have a broad prospect in the field of space robotics, as a significant number of organizations and researchers have been investing in the design and development of sophisticated rovers for planetary exploration. In order to promote research and development in the design of next-generation MARS rovers, an annual University Rover Challenge (URC) is hosted by the MARS Society in the United States. In this study, we highlight the design and development process of several novel subsystems of a human-assistance planetary exploration rover and their successive integration in the prototype named PHOENIX, which is a rover that participated in the URC 2021. First, a detailed requirement elicitation has been conducted, for designing a conceptual framework for a rover capable of planetary exploration. Secondly, the design and development process has been detailed for five basic subsystems (power, communication, primary-manipulator, chassis with drive, processing) and two mission-specific subsystems (scientific exploration and autonomous navigation), as well as their successive integration into the rover. Afterwards, a detailed evaluation study has been conducted in order to validate the performance of the developed system. Terrain traversability, autonomy in navigation, and sophisticated task execution capabilities have been evaluated individually within this study. Additionally, the capability of the rover in detecting bio-signatures from soil samples using a novel Multiple Bio-molecular Rapid Life Detection (MBLDP-R) protocol has also been evaluated. The developed scientific exploration subsystem is capable of detecting the presence of life from soil samples with a 92% success rate, and from rock samples with a success rate of 93.33%.
... The dust was believed to be a comparable substitute to the fine oxide particulates that would be expected in a decommissioning environment (Haskins, 1995). The contamination testing work is discussed at length by Banos et al. (2021), where the cleanup effort was compared to that required for a Hexapod robot. The Hexapod robot was found to spread the contamination significantly less due to its smaller ground contact area, however, as with Vega the contamination was difficult to remove completely. ...
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This paper presents the Vega robot, which is a small, low cost, potentially disposable ground robot designed for nuclear decommissioning. Vega has been developed specifically to support characterization and inspection operations, such as 2D and 3D mapping, radiation scans and sample retrieval. The design and construction methodology that was followed to develop the robot is described and its capabilities detailed. Vega was designed to provide flexibility, both in software and hardware, is controlled via tele-operation, although it can be extended to semi and full autonomy, and can be used in either tethered or untethered configurations. A version of the tethered robot was designed for extreme radiation tolerance, utilizing relay electronics and removing active electronic systems. Vega can be outfitted with a multitude of sensors and actuators, including gamma spectrometers, alpha/beta radiation sensors, LiDARs and robotic arms. To demonstrate its flexibility, a 5 degree-of-freedom manipulator has been successfully integrated onto Vega, facilitating deployments where handling is required. To assess the tolerance of Vega to the levels of ionizing radiation that may be found in decommissioning environments, its individual components were irradiated, allowing estimates to be made of the length of time Vega would be able to continue to operate in nuclear environments. Vega has been successfully deployed in an active environment at the Dounreay nuclear site in the UK, deployed in nonactive environments at the Atomic Weapons Establishment, and demonstrated to many other organizations in the UK nuclear industry including Sellafield Ltd, with the goal of moving to active deployments in the future.
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The generalized approaches of mathematical modelling for numerical simulating and processing of measured electrical signals from board sensors installed on wheeled electro-mech­an­ical platforms are developed in this research. The mathematical backgrounds of the developed approaches are elaborated on the basis of especially formulated initial-value problems need to be solved numerically or the identification procedure need to be applied. It is shown that using the Lagrange's formalism and the electro-mechanical analogies for constructing the improved coupled mathematical models both the mechanics and electrics and electronics of the wheeled platforms and the installed board sensors and the measuring electronic transducers allows having the more information if processing of the measured signals will be on the basis of such improved mathematical models. It is considered the particular example of using the proposed approaches dealt with simulating and processing the measured electric signals from the board accelerometer installed on the four wheeled electro-mechanic platform. Due to this example it was shown that using of the improved mathematical models allows the significantly wider possibilities of accelerometer measuring, so that the different parameters can be estimated by means processing the direct accelerometer measures using the corresponded mathematical models. It was shown that, the most difficulties of identification problems for processing the measured signals from the board sensors installed on the wheeled platforms are due to inherent them the mathematical incorrectness according to Hadamard. The effectiveness of using the filtering of the results of processing the measured signals is shown for the considered particular example of the identification problem also.
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Emulating the highly resource-efficient processing of visual motion information in the brain of flying insects, a bio-inspired controller for collision avoidance and navigation was implemented on a novel, integrated System-on-Chip-based hardware module. The hardware module is used to control visually-guided navigation behavior of the stick insect-like hexapod robot HECTOR. By leveraging highly parallelized bio-inspired algorithms to extract nearness information from visual motion in dynamically reconfigurable logic, HECTOR is able to navigate to predefined goal positions without colliding with obstacles. The system drastically outperforms CPU- and graphics card-based implementations in terms of speed and resource efficiency, making it suitable to be also placed on fast moving robots, such as flying drones.
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Book
This vOlume contains the invited and contributed papers pre­ sented at the American Nuclear Society (ANS) meeting on Decontamina­ tion and Decommissioning (D & D) of Nuclear Facilities, held Septem­ ber 16-20, 1979, in Sun Valley, Idaho. This was the first U. S. meeting of the ANS which addressed both of these important and related subjects. The meeting was attended by more than 400 engineers, scientists, laymen, and representatives of federal, state, and local governments, including participants from eleven foreign countries. The technical sessions included several sessions concentrating on ongoing D & D programs in the U. S. and abroad. In addition, "new ground" was broken in such areas as decommissioning costs and cost recovery, advanced programs on reactor coolant filtration, and other areas of continuing and increasing importance to the nuclear industry and to consumers. The dual sponsorship of the meeting (The ANS Reactor Operations Division and the Eastern Idaho Section of the ANS) helped spur a high quality program, a pleasant location, and a high degree of suc­ cess in technical interchange between the attendees. As guest speaker, we were honored to have Mr. Vince Boyer of Philadelphia Electric Company. Mr. Boyer is both a past chairman of the ANS Reactor Operations Division and a past president of the American Nuclear Society. His views on the nuclear industry and of its current status were informative and interesting.
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Visual condition inspections serve as the basis for determining the need and schedule for service tasks such as maintenance and remediation projects to preserve the proper functioning of power facilities and infrastructure. An increasing accumulation of service projects has recently surfaced due to the lengthy, labour-intensive and subjective qualities of the current method for inspection. These processes are also costly due to the temporary closure of the infrastructure as well as the requirement of special inspection equipment. Unmanned aerial vehicles (UAVs), commonly known as drones, offer potential as a useful tool for infrastructure inspections. UAVs provide visual assessments of structures while eliminating the need for manual inspections. Thus, aerial systems have the potential to reduce the cost of inspections as well as limit the disruption of the public while allowing engineers to have a better three-dimensional understanding of the system. However, the implementation of UAV inspection includes several difficulties such as flight stability, control accuracy, and safety. This study summarises the context for UAV inspection of power facilities and structures. Technologies to address the hindrances preventing UAV integration into the current practice are reviewed. Existing challenges and future work in research for UAV inspections are also presented.