Robots were developed to reduce the human work and increase the precision of work. Now, this can be applied to radioactive environment encountered in nuclear power plants. As human safety is of primary importance, so robots are taking over from human beings in radioactive environment.
Now different types of telerobots are used in the nuclear power plants which can access anywhere in the nuclear power plants, thus reducing human exposure. Apart from the high initial cost, it is cheaper than using professional workers in long run.
The future of robots used in radioactive environment is expected to reach a phase where the nuclear power plants can be made devoid of human beings. This would be possible only with the arrival of completely automatic fractal robots.
Robots In Radioactive Environments.doc
(Size: 367 KB / Downloads: 359)
CHAPTERS PAGE NO
1. INTRODUCTION 1
2. BRIEF HISTORY 2
3. BASIC COMPONENTS OF A ROBOT 3
3.1. MANIPULATOR 3
3.2. END EFFECTOR 4
3.3. POWER SUPPLY 4
3.4. CONTROLLER 4
4. NEED FOR ROBOTS IN RADIOACTIVE 6
5. TYPICAL NUCLEAR TELEROBOTIC APPLICATIONS 7
IN PRESSURISED LIGHT WATER REACTORS
6. ROBOTS USED IN NUCLEAR POWER PLANTS 8
6.1. REMOTELY OPERATED SERVICE ARM 8
6.2. INSPECTION AND RETRIEVING VEHICLE 9
6.3. CLEANING AND RETRIEVING VEHICLE 9
6.4. TRON 9
6.5. ELECTRIC MASTER SLAVE MANIPULATOR 10
6.6. SNAKE LIKE ROBOTS 10
6.7. ARK 12
7. FUTURE USE OF ROBOTS IN RADIOACTIVE 15
7.1. CHARECTERISING AND LIMITING NUCLEAR 16
7.2. NEGOTIATING UNDEFINED TERRAIN USING 16
A TRUE MULTI-TERRAIN VEHICLE
7.3. REACTOR CORE MELT DOWN 17
7.4. POWER STATION DESIGN OF THE FUTURE 17
8. CONCLUSION 19
LIST OF FIGURES
1. FIG 3-1 MANIPULATOR 3
2. FIG 3-2 BLOCK DIAGRAM OF A CONTROLLER 5
3. FIG 3-1 ROSA
Robots are developed to be used in areas inaccessible to human beings. Radio active environment is one in which high energy radiations like α, β and γ radiations are emitted by radioactive materials. There is a limitation in case of the time and dose for which professional worker can be exposed to nuclear radiations according to international regulations so it very useful to use robots in such an environment.
Robots with properly automated can also be used to control nuclear power plants and hence can be used to avert nuclear power plant disasters like one that occurred at Chernobyl. Robots can also be used for the disposal of radioactive waste.
Future is still bright for robots in radio active environment as they are to be used to isolate nuclear power plants from surroundings in case of a nuclear power plant disaster.
The word robot was introduced in 1921 by the Czech play Wright Karel Capek, in his play Rossum’s universal robots and is derived from the Czech word “Robota”, meaning “forced labour”. The story concerns a brilliant scientist named ‘ROSSUM’ and his son, who developed a chemical substance similar to protoplasm to manufacture robots. Their plan was that the robots would serve the mankind obediently and do all physical labour. Finally, after improvements and eliminating unnecessary parts, they develop a “perfect robot”, which eventually goes out of control and attacks humans.
Although Capek introduced the word robot to the world, the term robotics was coined by Isaac Asimov in his science fiction story “run around”, where he portrayed robots not in negative manner but built with safety measures in mind to assist human beings. Asimov established in his story three fundamental laws of robots as follows:
1. A robot may not injure a human being or, through inaction, allow a human being to come to harm.
2. A robot must obey the orders given to it by human beings, except where such orders would conflict with the first law.
3. A robot must protect its own existence as long as such protection does not conflict with the first and second laws. .
Robots were introduced into the industry in the early 1960’s. Robots originally were in hazardous operations, such as handling toxics and radioactive materials and loading & unloading hot work pieces from furnaces and handling them in foundries.
BASIC COMPONENTS OF A ROBOT
The basic components of any complex industrial robot are as follows:
The manipulator is a mechanical unit that provides motion similar to that of a human arm. Its primary function is to provide the specific motions that will unable the tooling at the end of the arm to do the required work. The individual joint motions are referred to as degrees of freedom. Typically, industrial robots are equipped with 4 to 6 degrees of freedom. The wrist can reach a point in space with specific orientation by any of the three motions: a pitch or up- and- down motion; a yaw, or side- to- side motion; and a roll, or rotating motion. The manipulator, therefore, is apart of the robot that physically performs the work. The points that a manipulator bends, slides or rotates are called joints or position axes. Manipulation is carried out using mechanical devices, such as linkages, gears, actuators and feedback drives.
Fig 3-1: Manipulator
3.2 End Effecter
A robot can become a production machine only if a tool or device has been attached to its mechanical arm by means of the tool mounting plate. Robot tooling is referred to as end of arm tooling (EOAT) is commonly used both by industry and in publications. If the end effecter is a device that is mechanically opened and closed, then it is called a gripper. If the end effecter is a tool or a special attachment, then it is called process tooling.
Depending on the type of operations, conventional end effectors are equipped with various devices and tool attachments as follows:
Grippers, hooks, scoops, electromagnets, vacuum cups and adhesive fingers for material handling.
Spray gun for painting.
Attachments for spot and arc welding and arc cutting.
Power tools, such as drills, nut drivers and burrs.
Special devices and fixtures for machining and assembly.
Measuring instruments such as dial indicators, depth gauges and the like.
3.3 Power Supply
The function of the power supply is to provide and regulate the energy that is required for a robot to be operated. The three basic types of power supplies are electric, hydraulic and pneumatic. Electricity is the most common source of power and is used extensively with industrial robots. The second most common is pneumatic and the least common is hydraulic.
The controller is a communication and information processing device that initiates, terminates and coordinates the motion and sequences of a robot. It accepts the necessary inputs to the robots and provides the output drive signals to a controlling motor or actuator to correspond with the robot movements and outside world.
Controllers vary greatly in complexity and design. They have a great deal to do with functional capabilities of a robot and therefore, the complexity of the tasks that robots must be able to fulfil.
The heart of the controller is the computer and its solid state memory. In many robot controllers, the computer includes a network of microprocessors.
The input and output section of a control system must provide a communication interface between the robot controller computer and the following parts:
Feed back sensors
Production machine tools
Program storage devices
Other computer device hardware
Fig 3-2: Block Diagram of a Controller
NEED FOR ROBOTS IN RADIOACTIVE ENVIRONMENT
Radioactive environment is mainly encountered in nuclear power plants. Some regular repair and maintenance activities at nuclear power plants involve risks of contamination and irradiation. While contamination is an accidental and avoidable phenomenon, irradiation is continuous and effects the operators work areas. Various countries have laws establishing annual maximum doses to which professional workers can be exposed and the maximum time that they may stay inside areas subject to radiation.
Most tasks at nuclear facilities are carried out by in house maintenance specialists. They are few in number and in many cases, require several yeas of experience and extensive training programs. The number of hours that they can work continuously is limited by national international regulations regarding the maximum dose that may be received by exposed professional workers. Legal regulations establish that when a worker reaches a specific dose limit, the worker cannot work in areas subject to radiation for a given period of time. This increase the cost of maintenance services because personal only operate for short periods of time. Given the discontinuous use of human resources and discontinuous nature of work, nuclear service companies are obliged to allow for some uncertainties in scheduling of services and in rationalization of their human resources.
For all the above reasons, it is generally advisable and in some cases mandatory, to use telerobotics for the execution of repair and maintenance tasks in nuclear power plants. This is particularly true of tasks entailing high exposure to radiation.
TYPICAL NUCLEAR TELEROBOTIC APPLICATIONS IN PRESSURISED LIGHT WATER (PWR) REACTORS
These are some of the typical surveillance and maintenance operations in pwr units where telerobotic systems can be applied.
1. Steam generator
Primary tube inspection and maintenance.
Channel head cleaning and decontamination.
Nozzle dam insertion.
Secondary side foreign object removal.
Foreign object removal in the primary circuit.
2. Reactor cavity
Floor and wall area decontamination.
Fuel transfer channel cleaning.
Fuel transfer channel and underwater inspection.
3. Reactor vessel
Underwater inspection and repair.
Foreign fallen object removal.
Lower internal inspection.
4. Reactor head vessel
Internal pipe inspection and object removal.
Underwater cleaning of various plant tanks and vessels.
Surface decontamination of general floor areas.
Underwater inspection of equipment and spent fuel pools.
Extraction and welding of the pressurized heaters.
ROBOTS USED IN NUCLEAR POWER PLANTS
6.1. Remotely operated service arm (ROSA)
Radioactive environment in which robots work is actually seen in nuclear power plants. The tubes in steam generators are subject to multiple stresses, such as mechanical and thermal loading, vibrations and various types of corrosion. Diagnostic tests are therefore necessary to identify points of degradation along the SG tubes and define repair procedures for damaged tubes. The SG maintenance jobs, which are carried out during plant refuelling outages, involve complex tasks (water cleaning, nozzle dam insertion, eddy-current inspection, mechanical plugging and unplugging etc) inside an environment made hazardous by high radiation and contamination. The frequency of inspection and the number of inspected tubes increases with the aging of the plant. So a telerobotic system known as remotely operated service arm is used to the use of jumpers that work inside the SG channel head, thus lessens the risk of contamination of human workers. The system has proven its robustness and flexibility for a wide range of maintenance operations inside the SG channel head of PWR SGS. The system provides a remote user interface for controlling the joint six axis arm. The arm is equipped with a remote quick connector (RQC) to facilitate the assembly and disassembly of such tools.
Fig 6-1: ROSA
6.2. INSPECTION AND RETRIEVING VEHICLE (IRV)
During maintenance operations inside the SG channel heads, objects may accidentally fall inside the primary circuit nozzle. When this happens, it is necessary to develop special tools to remove fallen objects. These tools are often handled by jumpers from the channel head nozzle, so the accumulated doses are very high. This is not particularly frequent incident, but because it has happened in past and entails high exposure to radiations for workers, nuclear plants demand that contingency procedures may be put in place. The inspection and retrieving vehicle system is a teleoperated vehicle provided with sensors, lights, cameras and interchangeable end-effectors that allow these operations to be carried out from safe place.
6.3. CLEANING AND RETRIEVING VEHICLE (CRV)
An amount of radioactive waste gathers as a result of the refuelling operation, transfer of fuel elements and general cleaning of the pool. This pit, located at the lowest level close to the transfer channel, is one of the hot points where workers are generally exposed to moderate but occasionally very high levels of radiation.
The design of cleaning and retrieving vehicle telerobotics system is based on the IRV. The CRV is a teleoperated vehicle that works underwater. It is equipped with a rotating brush to pick up the dirt and a pump to remove it to an external shielded filter.
During refuelling operation, parts of tools or other objects can fall into the vessel because of human error or other circumstances. The teleoperated and robotized system for maintenance operation in nuclear power plant vessels is a four jointed robotized pole used to retrieve fallen objects from the PWR reactor vessel. The pole is inserted through the holes in the lower core plate. In this way, it can inspect the lower internal zone and recover objects without the core having to be disassembled.
The whole system comprises a jointed pole, end-effectors and a computer vision navigation system that helps the operator to move through a highly complex environment. The end-effector and the inspection cameras are attached to the end link. More complex mechanism cannot be used because of the small size of the flow holes.
6.5. ELECTRIC MASTER SLAVE MANIPULATOR
The EMSM range of Electrical Master Slave Manipulators has been developed for use in high dose environments where intricate and/or heavy duty work is carried out.
Master arms operated by the user transfers exact motions kinematically to the slave manipulator. Throughout the process, the user is given a realistic feeling of forces and moment as, import
Realistic force feedback
Effortlessly handles loads of up to 100 kg
All purpose manipulator designed to be used with standard tools: grinders, drills, screwdrivers.
6.6. SNAKE-LIKE ROBOTS
When disasters like nuclear power plant explosions occur, power plant personnel are often faced with a problem: how to find the reasons for nuclear power plant explosions, so that future disasters can be avoided. The answer may be robotic animals that can venture to hard to reach places that are inaccessible to people.
Mother Nature as Muse
Robotic researchers are looking more and more to mimic nature for the shapes and functions of their mechanical creations. At North Carolina State University, when students were challenged to come up with a robot that could crawl through pipes, they looked to the animal world for a clue.
The idea came to Eddie Grant, director of the Center for Robotic and Intelligent Machines and a visiting professor at NC State, when he spoke with a major in the Marine Corps who had been called out to the Oklahoma City bombing. Grant realized that a robot that could navigate pipes would be ideal in this situation because pipes generally stay intact when the rest of a structure has collapsed.
The senior design students created robots called MOCASIN I and MOCASIN II (Modular Observation Crawler And Sensing Instrument) that can crawl through six-inch piping
How Does It Work?
MOCASIN II is a segmented robot that looks somewhat like an inchworm. It uses pneumatics (air pressure) to force padded "feet" against the pipe walls, contracting and expanding its "body" in the process. The use of pneumatics for movement is an important factor because sometimes there are explosive gases present in nuclear power plants that have exploded. Since electricity might ignite the gases, the robot uses compressed air, which also allows it to run off of air tanks when no electricity is available. The robot is designed so that it breaks down into components that can be easily transported to remote sites.
A tiny video camera and lights allow rescuers to see where MOCASIN II is located. The robot can also be equipped with sensors that could pick up vibrations from someone tapping on the pipes, or even "hear" voices and perhaps breathing.
What Else Could It Do?
Robots like MOCASIN II could eventually have other uses, as well. They could be used for repairs in dangerous areas, such as nuclear power plant pipes, or to detect cracks in sewer or water lines. They could used to rescue people from rubbles after massive earthquakes. They could be even used in other planets.
Researchers at NASA’s Ames Research Center are currently developing robots that resemble snakes to be used on the unknown terrain of other worlds. The snake-like design has several advantages. It allows the robots to be flexible and adaptable, plus they can fit into tight spaces and move over large objects. The Serpentine Robotics Project is working on adding pressure and light sensors to the robots as well. Like the MOCASIN, the robots use standard parts and electronics, but in this case they really resemble snakes. Robotic snakes that even imitate the slithering movement of the real thing, has been developed.
While it may be a while before snake robots are used in space, rescuers on this planet are likely to find such robots an invaluable tool.
6.7. AUTONOMOUS ROBOT FOR KNOWN ENVIRONMENT (ARK)
The ARK (Autonomous Robot for a Known Environment) Project was a precompetitive research project involving Ontario Hydro, the University of Toronto, York University, Atomic Energy of Canada Ltd., and the National Research Council of Canada. The project started in September 1991 and completed in August 1995. The technical objective of the project was to develop a sensor-based mobile robot that could autonomously navigate in a known industrial environment.
There are many types of industrial operations and environments for which mobile robots can be used to reduce human exposure hazards, or increase productivity. Examples include inspection for spills, leaks, or other unusual events in large industrial facilities, materials handling in computer integrated manufacturing environments, and the carrying out of inspections, the cleaning up of spills, or the carrying out of repairs in the radioactive areas of nuclear plants - leading to increased safety by reducing the potential radioactive dose to workers.
The industrial environment is significantly different from office environments in which most other mobile robots operate. The ARK project produced a self-contained mobile robot with sensor-based navigation capabilities specifically designed for operation in a real industrial setting. The ARK robot was evaluated in the large engineering laboratory at AECL CANDU in Mississauga, Ontario. This open area covers approximately 50,000 sq. feet of space and accommodates one hundred and fifty employees. Within the Laboratory, there are test rigs of various sizes, mockups of reactor components, a machine shop, a fabrication facility, a metrology lab and assembly area. There are no major barriers between these facilities and therefore at any one time there may be up to fifty people working on the lab floor, three fork lift trucks and floor cleaning machines in operation. Such an environment presents many difficulties that include: the lack of vertical flat walls; large open spaces (the main isle is 400' long) as well as small cramped spaces; high ceilings (50'); large windows near the ceiling resulting in time dependent and weather dependent lighting conditions, a large variation in light intensity, also highlights and glare; many temporary and semi-permanent structures; many (some very large) metallic structures; people and forklifts moving about; oil and water spills on the floor; floor drains (which could be uncovered); hoses and piping on the floor; chains hanging down from above, protruding structures, and other transient obstacles to the safe motion of the robot.
Large distances, often encountered in the industrial environment, require sensors that can operate at such ranges. The number of visual features (lines, corners and regions) is very high and techniques for focusing attention on specific, task dependent, features are required. Most mobile robotic projects assume the existence of a flat ground plane over which the robot is to navigate. In the industrial environment this ground plane is generally flat, but regions of the floor are marked with drainage ditches, pipes and other unexpected low lying obstacles to movement. The ARK robot required sensors that can reliably detect such obstacles.
The ARK robot's onboard sensor system consisted of sonar’s and one or more ARK robotic heads and a floor anomaly detector (FAD). The head consists of a colour camera and a spot laser range finder mounted on a pan-tilt unit. The pan, tilt, camera zoom, camera focus and laser distance reading of the ARK robotic head are computer controlled.
The ARK robot must navigate through its environment autonomously and cannot rely on modifications to its environment such as the addition of radio beacons, magnetic strips beneath the floors, or the use of visual symbols added to the existing environment. In order to navigate within this environment the ARK robot used naturally occurring objects as landmarks. The robot relied on vision as its main sensor for global navigation, using a map of permanent structures in the environment (walls, pillars) to plan its path. While following the planned path, the robot locates known landmarks in its environment. Positions and salient descriptions of the landmarks are known in advance and are stored in the map. The robot uses the measured position of the detected landmarks to update its position with respect to the map.
FUTURE USE OF ROBOTS IN RADIOACTIVE ENVIRONMENT
Robots have to be used in handling nuclear materials because of its toxic effects on life. Nuclear accidents are the most difficult to deal with at present and experience has shown that humans can only run away from nuclear accidents in the face of danger just like a comical Neolithic ancestors running away in the face of fire. Fractal robots presented here explains in detail how best to manage nuclear accidents.
At its simplest a fractal robot is simply a collection of computer controlled bricks that reshape on command into different structures in a matter of seconds. It’s like kids playing with Lego-instead we use a computer and motorised bricks and do this with total automation.
Fractal robots can limit an evolving nuclear accidents as it occurs by sealing the roof top of the building that have been blown and leaking radiation dusts. Penetrating intense radiation from nuclear accident can prevent any kind of repair work from being undertaken inside the building. This penetrating nature of radiation requires that all machinery be operated remotely. Standard remote machinery such as robotic rovers cannot operate in high radiation environments, confined spaces or an undefined terrain created by explosions that simply rules out existing approaches. Fractal robots on the other hand can overcome all these difficulties systematically because it is a true multi-terrain vehicle to get from anywhere to anywhere across undefined terrains.
7.1 Characterising and Limiting Nuclear Accident
A nuclear reactor that has been severely damaged is never accessible directly for servicing or repairs. The concrete reactor is normally surrounded by installation specific buildings that can make access difficult after an accident. Access constrains make the task of clearing up catastrophic reactor failure near impossible using conventional systems.
It is the chemical or pressure explosion or both that rips the dome of the reactor and destroys other parts of the installation. These kinds of explosions are typical of explosions that have ripped through the installations in the past. There is debris everywhere and terrain is generally undefined. A legged robot could become trapped in the debris and so would small robots which are of little use anyway once they reach their objectives. Large robots cannot enter the building and tread its way through the maze of the machinery without creating further damage.
If the installation is fitted with fractal robots, they can kick into action seconds after an accident even if they are damaged because they are self repairing machines. The first priority of the robots is to negotiate the rough terrain and arrive at the accident scene. Operators are used to shuffle the bricking position aided by computer software that calculates deformation algorithms and routes for moving cubes to cope in undefined terrain.
7.2 Negotiating Undefined Terrain Using a True Multi-terrain Vehicle
The fractal robots squeeze through small holes by shuffling the bricks around. They take with them cameras, lighting and any other special equipment integrated into the cubes and which can squeeze through the available holes. Under operator control, the fractal robots can then install lighting and cameras. Dust suction equipment and/or hoses can be installed to filter out dust and fumes. The robotic cubes can be used as structural supports to support collapsing ceilings. Terrain that is not a problem for the robotic cubes which can transform into foot units that allow the machine to support itself whilst negotiating hallways and corridors. The possibility of malfunction of electronic systems is avoided using lead shielding and using specialized robotic cubes that have no electronics and have the equivalent of a mechanical computer inside it built out of relays.
7.3 Reactor Core Melt Down
Fractal robots can handle the worst case reactor core meltdown accident. If the reactor is eating its way through the ground as happened in Chernobyl, we can stop it. The problem with such a reactor is that in the molten state it is hot and corrosive. The melt cannot be cooled with normal fluids as they can be vaporised by the heat generated by radioactive molten core which will continue to generate heat for days if not weeks. The molten core has to cool by the equivalent of a nuclear coolant such as molten lead. By amalgamating the molten lead with molten core, the nuclear reactions are shut down. Whatever the coolant used, actions has to be taken immediately if the molten core is not to eat its way through all the reactor building floors and seep into the ground from where it can be very difficult to extract.
7.4 Power Station Design of The Future
Fractal robots are competitive when the full nuclear power production cycle is taken into account. This includes decommissioning work which is now estimated to run into billions of dollars per installation. Fractal robots are also competitive in the disposal of radio active wastes. It is not possible to simply take tons of equipment and bury it somewhere with out due attention and care to the possibilities of radioactive substances leeching into the environment over the decades. Fractal robots can help in a number of ways to reduce the amount of waste generated and to look after those wastes.
For example, if much of the low activity structure is made of fractal robot compatible structures, then they can be recycled in other installations or even in the current installations in more radioactive areas as they acquire higher and higher dosages until they end up in the reactor room as reactor supports and lining. Instead of commissioning more new installations which will then get contaminated, the old structures from the old reactors are de-installed and reused in the newer installations to acquire a higher dosage. Fractal robots give hundred percent automation and thus there is no need for humans to go into reactor areas or contaminated areas for any reasons for this type of reactor.
With the level of automation offered by fractal robots, when new reactors are commissioned, the old structures that have been de-commissioned are retrieved from storage and reused. This recycling minimizes creation of nuclear contaminated wastes. De-commissioning can also be carried out using same robots. De-commissioned robotic parts held in storage can be looked after by more fractal robots patrolling, the waste site with sensors to look for leaks and leeching.
Over the years, several telerobotic systems for periodic maintenance services and unforeseen interventions have been developed. Most of the process that is inaccessible to human has been automated. Thanks to the design of reference software architectures for teleoperated systems, it has been possible to develop different applications reusing existing components.
But even after all these developments, complete automation still remains a challenge. It’s believed that complete automation would be possible with the development of fractal robots.
1. Keramas James G., “Introduction to Robots” ; McGraw-Hill
2. Kim, S; Jung, S.H.; Kim, C.H. , “Preventive Maintenance and Remote Inspection of Nuclear Power Plants Using Telerobotics” IEEE 1999.
3. Alvarez, B.; Iborra, A.; Alonso, A.; de la Puente, J.A.; Pastor, J.A.; “Developing Multi-application Remote Systems”,Nuclear Engineering Int. vol 45, March 2000.
4. Pastor, J.A.; Alvarez B.; Iborra, A.; Fernandez, J.M.: “An Underwater Teleoperated Vehicle for Inspection and Retrieving”,1st Intl. Symposium; Brussels ,November 1998.
5. Iborra, A; Alvarez, B.; Navarro, P.J.; Fernandez, J.M.; Pastor, J.A: “Robotized System for Retrieving Fallen Objects Within the Reactor Vessel of a Nuclear Power Plant”,Intl.Symposium, Industrial Electronics, Mexico; IEEE 2000.