Download - Remote Handling Technology in Nuclear Industry

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22 MODERN MANUFACTURING INDIA - MAY 2013

MAIN FEATURE

Radioisotopes are used in the areas of power production, health care, industry,

agriculture, food preservation, etc. Due to their potential health hazards, high-active

isotopes are handled remotely using remote handling devices. This article describes

general-purpose remote handling devices developed by Bhabha Atomic Research Centre.

Remote Handling Technologyin Nuclear Industry

In India, the program ‘Isotopes and

Radiation for Betterment of Humankind’

was initiated more than fifty years ago by

Dr Homi Jahangir Bhabha, the father of

energy in the form of radiation. They may

emit alpha particles, beta particles or

gamma rays. In addition to the above, a

nuclear facility may also have neutron

radiations, which are emitted from neutron

sources or the core of nuclear reactors.

These ionizing radiations have varying

penetrating powers and can be a health

hazard in varying forms.

Radiation protectionOccupational workers have to be protected

from ionizing radiations to eliminate the

possibility of health hazards. Radiation

exposure can be minimized by controlling

the following three factors:

▶ Time

Reducing the time of exposure reduces

the effective dose proportionally

▶ Distance

Dose is inversely proportional to the

square of the distance to the source

▶ Shielding

Placing a radiation absorbing material

between the operator and the source

will reduce the dose

K Jayarajan, FNAEHead, Tele-Manipulator SectionDivision of Remote Handling and RoboticsBhabha Atomic Research Centre, [email protected]

Remote handling tools enable an operator to

perform a task in a hazardous environment,

while remaining at a safe distance from the

task area

S o u r c e : B A R C / C H R I S T

I A N D A R K I N / S C I E N C E P H O T O

L I B R A R Y

India’s Atomic Energy Program. While the

isotopes of Uranium, Plutonium and

Thorium are used for power production,

radioisotopes produced in nuclear reactors

are used in a variety of applications,

including agriculture, food preservation,

water resource management and many

others. They are also used for diagnosis and

treatment of cancer.

Radioisotopes are atoms with unstable

nuclei, which may stabilize by releasing


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MODERN MANUFACTURING INDIA - MAY 2013 23

MAIN FEATURE

In India, the dose limits for occupational

worker and public are governed by the

regulations of Atomic Energy Regulatory

Board (AERB). In addition to the regulatory

requirements, the As Low As Reasonably

Achievable (ALARA) principle is followed

in designing and operating radiation

facilities for further reducing the dose.

Radioisotope handling

High-active isotopes are handled in nuclear

facilities for power production, fuel

reprocessing, nuclear waste management,

post irradiation examination, radioisotope

production, decommissioning, etc. Alpha-

emitting isotopes are handled in sealed

containers, called glove boxes, whereas

gamma-emitting isotopes are handled in

heavily shielded rooms, called hot cells. To

prevent leakage of contamination, the

outgoing air is filtered using high-efficiency

particulate air (HEPA) filters. Also, the air

pressure in the cell is maintained below that

of outside air. Usually, radiation shielding

windows (RSWs) are provided on the

shielded cell walls to get the view of cell

interior. RSWs shield gamma rays, but

allow visible light to pass through. As the

entry of human operator is restricted in hot

cells, objects in these cells can only behandled using remote handling devices.

Remote handling tools

Remote handling tools enable an operatorto perform a task in a hazardousenvironment, while remaining at a safe

distance from the task area. A goodremote handling device should be capable

of quickly performing the job at a distance

or behind a shielding. Remote handling

strategy depends on the risk, complexity

and the frequency of operation of thetask. Automation can be adopted forrepetitive tasks in a structured area.However, unstructured tasks requiredexterous human intervention in real-time.

Designing a device for radioactiveenvironments has many challenges. Many

common materials and most of the

conventional electric and electronic

components have a short life in high

radiation. The device has to be designed for

remote maintenance and should be capable

of withdrawing from the remote area, if

necessary. The components should not get

damaged, when they are washed with water

or mild acids for decontamination.

Bhabha Atomic Research Centre (BARC)

has developed many types of multi-purpose

remote handling devices, including Remote

handling tongs, Mechanical master slave

manipulators, Servo manipulators, Power

manipulators and Autonomous vehicles. A

few of them are described here.

Master slave manipulators

Master slave manipulators (MSMs) are the

most widely used remote handling tools in

the nuclear industry. They can reproduce

the natural motions of human in 1:1 ratio,

on a gripper located in the remote hot cell.In master slave manipulation, the human

being is within the process; his manipulative,

sensory and decision-making capabilities

are extended to the remote site.

The tool has two arms, a master arm in the

operating area and a slave arm in the remote

site. The master arm has a handgrip and the

slave arm has a gripper at their free ends.

When the operator holds the master handgrip

and moves it along the desired path, the slave

gripper reproduces the motion in the remote

hot cell. The force and torque applied by theoperator also gets reproduced on the slave

gripper. The operator can get visual feedback

of the hot cell, through the RSW (viewing

window) or CCTV cameras.

S o u r c e : B h a b h a A t o m i c R e s e a r c h C e n t r e Remote handling experience in

nuclear industry has been useful

elsewhere also. At the Ordnance

Factory Khamaria, Jabalpur, about300 ammunition boxes, containing

anti-tank mine fuzes, were lying in

two rooms for more than 25 years.

The fuzes, being highly explosive,

were threat to the factory and the

surroundings. BARC has developed

a remote handling system

consisting of a vehicle, a

manipulator and a box-handling

device. Using the system, the fuzes

were safely taken out from the

rooms, transported to a remote

site and disposed successfully.

Explosive disposal system

S o u r c e : B h a b h a

A t o m i c R e s e a r c h C e n t r e

Four-piece servo manipulator. The modular manipulator can be installed in any type of hot cells.

Slave Arm

MasterHandgrip

MasterArm

MotorAssembly

Through-Tube

Slave Gripper


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MAIN FEATURE

Like a human arm or a robot manipulator,

the slave arm of an MSM consists of a series

of links connected together through joints.

Usually, the arms would have minimum six

joints for arbitrarily positioning the gripper.

It may be noted that for specifying theconfiguration of an object in space, six

variables are necessary: three for position

and three for orientation. All joints are

controlled synchronously to achieve the

desired gripper trajectory.

Depending upon the power source of the

slave arm, MSMs are classified into

Mechanical MSMs and Electrical MSMs

(Servo Manipulators).

Mechanical master slavemanipulators

In a mechanical MSM, the master arm and

the slave arm are mechanically coupled

through a through-tube in the cell wall.

Required power for the remote operation

in the hot cell is supplied by a human

operator himself standing outside. A

mechanical MSM is a multi-degree-of-

freedom mechanism, with six manually

powered joints and a gripper. Sometimes,

at most three electrically powered joints are

provided to increase the range of the slave

arm and to improve the operator’s comfort.

An MSM may be of articulate type ortelescopic type. While all joints of the former

are of revolute type, the later would have at

least one prismatic joint. BARC has

developed a variety of mechanical MSMs

with varying reach (1 m to 3.4 m) and

varying payload (4.5 kg to 45 kg). They use

various mechanisms to convert the

operator’s hand movements in the operating

area into the movement of the slave gripper

in the hot cell. The joints are counter-balanced to reduce the operator’s effort.

Servo manipulators

The slave joints of servo manipulators are

powered by external power sources such as

electric motors or hydraulic actuators.

External power sources reduce operator’s

efforts. Moreover, the force that can be

applied by the slave arm is not limited by

the strength of the operator.

In servo manipulators, the master arm

and the slave arm are connected through

electric cables or by wireless communication.

This provides flexibility of mounting the

slave arm on a transporter, like a vehicle or

a crane. As this would enhance its range, one

pair of servo manipulator could serve a hot

cell of any size. The servo manipulator can

approach hot cell equipment from arbitrary

directions. It provides flexibility in design of

the equipment and the layout of hot cell.

Servo manipulator technology is a multi-

disciplinary field, similar to that of robotics.

It requires expertise in various areas like,

mechanical, electrical, electronics, controlsystem, software, nuclear and ergonomics.

Advanced technologies

BARC has been actively involved in

enhancing the quality of tele-operation. The

major research activities in this area include

telepresence and telerobotic technologies:

Telepresence

For fast and accurate tele-operation, the

operator should feel that he is present at the

remote site and is handling the objects

directly with his own hand. A telepresence

system consists of operator’s site and remote

site, equipped with effectors and sensors.

The operator’s site is equipped with visual,

hearing and haptic (touch) interfaces. The

remote site contains the slave manipulator,

camera and various sensors, with

information traveling between the user and

the remote location. Although, sensing

touch or force is inherent in a mechanical

MSM, they have to be artificially created in

a Servo manipulator. Stereo image isrequired for depth perception of the remote

site. A computer mouse can position the

curser on a 2-dimensional screen. However,

object manipulation in 3-dimension requires

simultaneous control of six variables.

Therefore, a master arm with six joints is

used as input device for tele-operation.

Tele-robotics

While robots are autonomous devices

capable of repetitive handling in structured

environments, MSMs are versatile devicessuitable for unplanned handling in

unstructured environment. A telerobot

combines both these capabilities- it can work

S o u r c e : B h a b h a A t o m i c R e s e a r c h C e n t r e

MSM Laboratory of BARC. BARC has developed about ten models of MSMs with varying payloads,

reaches and other features.

S o u r c e : B h a

b h a A t o m i c R e s e a r c h C e n t r e

Suspendable servo manipulator for emergency

operations: It can be attached to the hook of a

crane and taken to the site for remote operations.


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MAIN FEATURE

S o u r c e : B h a b h a A t o m i c R e s e a r c h C e n t r e

Advanced servo manipulator has force control capabilities. Also the operator can feel the force

acting on the remote gripper. These features are useful for safe handling of delicate objects.

as an MSM as well as a robot. Telerobots can

play a major role in hot cell automation, such

as in advanced fuel fabrication. Advanced

servo manipulators developed by BARC are

capable of operating as telerobot.

Conclusion

Radiation protection has been one of the

priority areas of the Department of Atomic

Energy (DAE). Identifying its importance,

DAE had initiated the development of

remote handling tools long ago. It has

successfully developed a variety of tools for

operations in radiation environments and

installed them at various nuclear facilities.

These tools virtually extend the operator’s

hand to a remote site and perform a variety

of jobs—from operation of small instruments

to the maintenance of large process

equipment. Telerobots are being developedto augment the versatility of human-assisted

tools with the autonomy of robots. MMI