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Nuclear Engineering and Design 241 (2011) 3719– 3728

Contents lists available at ScienceDirect

Nuclear Engineering and Design

j ourna l ho me page: www.elsev ier .com/ locate /nucengdes

volution in the design and development of the in-service inspection device forhe Indian 500 MWe Fast Breeder Reactor

shutosh Pratap Singha, C. Rajagopalana,∗, V. Rakesha, S. Rajendranb, S. Venugopala,.V. Kasiviswanathana, T. Jayakumara

Remote Handling, Irradiation Experiments and Robotics Division, Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam 603102, Tamil Nadu, IndiaDivision of Remote Handling and Robotics, Bhabha Atomic Research Centre, Mumbai 400085, India

r t i c l e i n f o

rticle history:eceived 2 December 2010eceived in revised form 11 July 2011ccepted 13 July 2011

a b s t r a c t

In-service inspection (ISI) plays a major role in monitoring the condition of nuclear power plant structuresand components. Based on the information gathered during inspection and the studies carried out, it ispossible to assess the extent of damage and take corrective measures to keep effects of ageing under con-

trol. In nuclear power plants comprehensive ISI is dictated by issues of increased safety to personnel andequipment, and efficiently enhances the plant life. A special emphasis has been laid on the developmentof robotic devices for the ISI of the indigenous Indian 500 MWe Prototype Fast Breeder Reactor (FBR)components. This paper traces the experiments and simulations in the key developments of a roboticdevice, for the ISI of main vessel and safety vessel of FBRs, carried out at Indira Gandhi Centre for AtomicResearch, India.

. Introduction

Nuclear power plants are poised to augment conventionalnergy sources by being safe, environmentally benign and eco-omically viable in order to meet the increasing per capita energyeeds of fast-growing economies like India. They are the energy

arms of the future. Research and implementations in nuclearngineering, more often than not, spawn the need to explorenabling technology developments for maximum efficacy. Theseevelopments have received a major fillip in recent times becausef various necessities which are quite singular to the nuclearomain.

Despite the best design and successful commissioning of nuclearlants preceded by stringent NDE-assisted quality control mea-ures, the synergistic effects of radiation, temperature and otheractors on the integrity of the plant components and structures can-ot be predicted or simulated. In this aspect, continuous monitoringnd inspection of critical components would only be the recourseo assess the integrity of the structures and components while thelants are in service. Such in-service inspection (ISI) operationshould also conform to the ALARA principle. The ISI of nuclear plants

s far more complex than that of conventional plants due to highadiation levels, making access to the components to be inspectedifficult. The compounded needs of inspection with limited access

∗ Corresponding author. Tel.: +91 44 27480208; fax: +91 44 27480356.E-mail address: crgopal@igcar.gov.in (C. Rajagopalan).

029-5493/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.nucengdes.2011.07.019

© 2011 Elsevier B.V. All rights reserved.

and high radiation level necessitate the use of remote inspec-tion techniques using robotic devices during ISI. Development andimplementation of new improved techniques and equipment tocarry out remote ISI is essential and could be justified by maxi-mum availability and safe operation of the plant for the successfulclosure of the nuclear fuel cycle. With India entering into the secondstage of the nuclear energy programme – fast breeder fuel cycle, itis imperative to successfully close and demonstrate the fuel cycle.

Several ISI devices have been developed and used in fast reac-tors all over the world especially in France (Asty et al., 1980), Japan(Matsubara et al., 1985; Rindo et al., 1993; Tagawa et al., 2007)and UK (Seed, 1986) for the ISI of main vessel and safety vessels.Magnetically attached vessel inspection system family of vehicleswas also developed for the ultrasonic inspection of TrawsfynyddNuclear Power Station Reactor Pressure Vessel (Burrows andYeomans, 1993). In the nuclear industry, stringent regulatoryaspects dictate the need to create mock-ups (often in real scale)to demonstrate the infallibility of any deployment. Hence, mock-upstudies are also carried out for various associated plant components(Kupperman et al., 2001), with a specific focus on the inspectionsystem peripherals (Ewen and James, 1988) before proceeding tothe actual deployment of ISI.

Hence in such a scenario, India’s first Prototype Fast BreederReactor (PFBR) construction of which is underway, warrants peri-

odic ISI which will be carried out using a special robotic device. Thishas led to the planning and development of a major ISI program asa deliverable at Indira Gandhi Centre for Atomic Research (IGCAR),India.

3720 A.P. Singh et al. / Nuclear Engineering and Design 241 (2011) 3719– 3728

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Fig. 1. Critical are

.1. ISI of PFBR

In Fast Breeder Reactors (FBRs), primary containment structure,rimary circuit equipment and reactor internals require remote

SI devices and techniques. The primary containment structuresomprise the main reactor vessel (MV), the safety vessel (SV), andhe reactor roof structure. One of the main in-service surveillanceequirements for the fast reactors is monitoring on the externaloundary of the main reactor vessel for evidence of primary liquidetal coolant leakage. This has to be performed on a continu-

us basis even when the reactor is at power. To supplement theontinuous surveillance of the integrity of the vessel volumetricxamination of the inters-space will be performed using Ultrasonicesting (UT) and Visual Examination (VE) of the approachable sur-aces will be carried out using a cooled CCD-based examinationystem, when the reactor is shut down. The inter-space betweenain vessel and safety vessel of the PFBR assembly is relatively

mall, typically about 300 mm. The inter-space is normally filledith nitrogen and the temperature during the inspection would

e 150 ◦C. Under such conditions, any inspection to be carried outust be done remotely using a customized device. The mandate for

he ISI campaign is to check the critical locations as delineated inig. 1.

The PFBR inspection programme is to be conducted accordingo ASME B & PV Code, Section XI, Div 3. There are six openings athe top of the reactor vault provided specifically for access to thennular space. A description of the ISI device, to be deployed inhe inter-space is elaborated in the following sections. The processonsists of removing relevant plugs, sealing the ISI openings andnti Convection Barrier (ACB) and then deploying the ISI device.

he binding requirement of maintaining the inter-space nitrogenressure, dictates the use of a comprehensive leak-tight system.he comprehensive system, for the campaign consists of the Air-ock Chamber (ALC) which houses ISI device. A cable take-up and

FBR requiring ISI.

release mechanism is utilized to hitch up and deploy the ISI device.A nitrogen inlet and outlet system replicates the MV-SV inter-spaceatmosphere. A Plug Handling Chamber (PHC) inside the ReactorContainment Building (RCB), provides the intermediate path andit also houses the various sealing plugs thereby utilizing the con-strained space optimally.

A marking scheme on the MV and SV of PFBR has been formu-lated and established to facilitate the location of the ISI device inthe MV-SV inter-space. The main vessel and safety vessel of theFBR are provided with a number of permanent reference marks ontheir external and internal surfaces respectively and coded withalphanumeric coding system. Using these reference marks, it willbe possible to locate and position the ISI device on the welds of theMV or SV surface in the MV-SV inter-space during the in-serviceinspection. Fig. 2(a) and (b) shows the prototype VE module devel-oped at IGCAR along with the images of the markings grabbed bythe camera.

2. ISI device – the experimental prototype

There are no permanent rails on the MV and SV surfaces, hencethe ISI device has to function using the walls of the vessels forfriction gripping in static condition and traction under dynamicconditions. The variation in the inter-space would be of the orderof ±50 mm. A gap-adaptable mobile device has been developed asa prototype to gain experience in the fundamental concept to carryout the ISI of main vessel and safety vessel remotely. The device isa tethered remote-controlled 4-wheeled vehicle with two wheelsresting on each vessel.

Once inserted into the inter-space, the ISI device can be

expanded to provide the reaction needed to maintain the devicein position against gravity. The wheels are kept pressed continu-ously on the surface by a pneumatic cylinder for gripping. The ISIdevice is capable of adapting in real-time to the variations in the

A.P. Singh et al. / Nuclear Engineering and Design 241 (2011) 3719– 3728 3721

Fig. 2. (a) Visual examination m

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Fig. 3. Principle of the experimental ISI device proto-type.

nter-space. The actuation for expanding/collapsing of the ISI deviceo adapt to the variation in the MV-SV inter-space is conformableor closed loop control using a load sensor. This suffices to sup-ort the self-weight of the device in the inter-space and enables

t to develop enough traction to move in any direction. The inher-nt principle has been depicted in Fig. 3 and the developed deviceas been shown in Fig. 4. The gap-adapting mechanism is actu-ted by a pneumatic cylinder operating at 8 bar pressure and with

bore diameter of about 100 mm. This enables the generation ofufficient force at each wheel-vessel contact point. The lever arm,ulled by the piston being smaller than the limb that protrudes, theechanical advantage of the system is less than 1.The device was configured with four wheels with two wheels

n each vessel surface and out of which one set of wheels is steered

imultaneous with a worm and worm-wheel linkage mechanismevoid of any traction. The other wheels at the ends of the leverslong the longitudinal meridian direction have independent steer-

Fig. 4. Prototype device for ISI.

odule and (b) the images.

ing. This set of wheels is also powered together and form the sourceof traction for the vehicle. Since the traction/steering motors are tobe housed together at the junction of the levers to ensure compact-ness, a chain-sprocket was required to transmit the motion from themotors to the ends of the lever. A couple of chain-sprockets transmitthe traction to each of the two end wheels and a similar set conveysthe motion for the independent steering of each of these wheels.Five stepper motors were used for achieving these motions andall of these were rated for room temperature use. The device wastested for movement in the inter-space created as a test-bench toreplicate the gap between main vessel and safety vessel. The devicehas a collapsible design to facilitate eventual insertion/retrievalthrough the openings provided from the operating floor, into thevessel inter-space.

The ultrasonic testing module and the visual examinationmodules together contribute 13.5 kg and 4.5 kg to the payload,respectively. The total weight for whole device figures to about80 kg. The collapsed width of the device is 190 mm which canexpand to about 350 mm. The length and breadth of the device are850 mm and 550 mm, respectively.

The wheel lining forms a crucial element in the work effec-tiveness of the whole principle and governs the performance ofthe device. The current device was tested with various set ofwheel linings of primarily two materials – VITON® (a fluorocar-bon compound) and PEEK, which is a thermoplastic used in hightemperature/radiation environs where it exhibits an excellent per-formance. Both grooved and smooth sets were used to test theeffect. The un-grooved VITON® lining failed to give the desiredresults due to bulging and subsequent tearing on application ofthe load. Similarly, the knurled PEEK lining could not give thedesired friction gripping. VITON® wheels with a grooved patternled to the most encouraging performance. Satisfactory gripping wasobserved with a smooth movement. This has led to the choice ofusing grooved VITON® linings for the PFBR ISI device (Section 3).

3. ISI device for the PFBR

The prototype ISI device, as described in the previous sectionexhibited the feasibility of a gap-adjusting mechanism and con-firmed the efficacy of device at room-temperature. The ISI devicefor the FBR would need to work at a temperature of 150 ◦C. All elec-tronic components need suitable thermal insulation or cooling totolerate the rigours of such an environment. This has necessitatedsome modifications in the design for the mechanical system also.

A major enhancement from the prototype ISI device has been the

removal of the chain-sprocket system. This transmission systemhas the inherent issues of lubrication using grease. Additional caremust be taken to maintain the tension using idlers, in the absence ofwhich the efficiency of the transmission suffers. Therefore, the basic

3722 A.P. Singh et al. / Nuclear Engineering and Design 241 (2011) 3719– 3728

the IS

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Fig. 5. CAD model of

raction, gap-adjustment and steering layout have been changed. Arushless DC traction motor has been attached to the middle set ofheels which still retain the common steering albeit with a sliding

our-bar link in the rocker-rocker mode, with geared transmissionf steering motion to the floating link. Two separate pneumaticylinders press the end wheels against the walls thereby enablinghe device to clamp between the vessels. These are also individuallyteered through a worm/worm-wheel. Hence, the total number ofotors has reduced to four as compared to the previous prototypehich used five motors in the motion transmission layout. This has

ontributed significantly to the weight reduction of the device. Theechanical advantage of the system is also enhanced to 1 for this

esign (as compared to the prototype), since pistons directly presshe wheels to the vessels. The model for the design is shown in Fig. 5.he total weight of the device, without payload, is about 90 kg.

A servo feedback control to work on a load-control loop woulde made available to avoid any loss of traction and overloading ofhe wheels. The design is such that the maximum reaction loadn each wheel is restricted to around 2450 N. This is a user require-ent to ensure the safety of the thermocouples, the covers of which

orm humps on the surface of the main vessel of PFBR. This also con-ributes to the requirement of a width-adjustable device to take uphe variations in the inter-space. The current pneumatic cylinders

ig. 6. Drive transmission layout of the ISI device for the PFBR under fabrication.

I device for the PFBR.

are capable of operating at 8 bar with a bore diameter of 50 mm.Each cylinder operates to generate a reaction force of about 1155 Nat the wheels. The bare vehicle and the drive elements are shownin Fig. 6, without the payloads.

The experimentation also revealed that cylinder pressures inthe range of 3.5–4 bar are sufficient to ensure the static grippingand motion of the device (at a maximum speed of 4 m/min) in theinter-space under dry wall conditions.

4. Design of the ISI device – for the future Indian FBRs

Future Indian FBRs would have reduced inter-space(240 ± 30 mm) due to economic considerations. The tighterspace constraints translate to tougher operating conditions forthe ISI devices. A changed concept is currently being explored forfeasibility with simulations. Essentially the linear motion of themiddle rods connected to a double piston cylinder of the four-barlinkage causes the terminal wheels to spread out and grip theinter-space walls. The two longitudinal end-wheels on either sideare kept pressing against the vessel surfaces using springs andhence they are passive, in this aspect. This principle is depicted inFig. 7. The wheels 6 and 7 are powered for traction and the rest ofthe wheels are passive.

There are 8 wheels, in total, and a diagonal set of middle wheelsand end wheels are steered simultaneously. The same motionoccurs on the other corresponding set. Traction is achieved by twoseparate motors giving torque, through a gear-set to one side mid-dle wheels (safety vessel side). This leads to the requirement of a setof four motors. The CAD model of this design is depicted in Fig. 8.This device has entailed a substantive weight reduction and thisdesign weights about 57 kg.

The wheel base length, in this design, has reduced to 675 mmfrom the current PFBR device length of 1000 mm. The fixed breadthof the device is 345 mm. The width of the vehicle (between thewheel edges) varies between 210 mm and 270 mm between thecollapsed and expanded conditions. The mechanical advantage ofthe device is evaluated as the amount of variation in the width ofthe vehicle for unit travel of the piston rod. This works out to the

tangent of the angle theta (Ref. Fig. 7). This value varies from 0.81to 2.82, as depicted graphically in Fig. 9.

Simulations for the static equilibrium of the vehicle, under theaction of gravity, reveal that the minimum required force of the

A.P. Singh et al. / Nuclear Engineering and Design 241 (2011) 3719– 3728 3723

Fig. 7. Principle of the ISI device for future FBRs.

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iston rod (per side) varies between 1148 N and 330 N as the devicexpands from collapsed condition to adapt to the maximum inter-pace gap (Ref. Fig. 10).

Force requirement on each piston should also satisfy equation1) for upward motion of vehicle due to the rolling of wheels 6 and 7gainst gravity. �ap is the applied torque on each wheel, M is vehicleeight, r stands for radius of middle wheel, �rr represents rolling

Fig. 8. CAD model of the

resistance torque and �min is the minimum mechanical advantageof the device.

Mgr + 2�rr < 2�ap < �r {(�min) F (piston) − 160} + 2�rr (1)

Hence, to ensure the infallibility of the vehicle adapting to thevariations in the inter-space in static and dynamic conditions, itis necessary to provide more than the minimum required force

future ISI device.

3724 A.P. Singh et al. / Nuclear Engineering and Design 241 (2011) 3719– 3728

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Fig. 9. Mechanical

rom Eq. (1) as an input on the pistons. Hence, a force of 3300 Ns maintained on the pistons by using a pneumatic actuator.

Kinematic simulation for the mechanism is carried out for60 mm inter-space gap of MV-SV with the vehicle hanging in ver-ical condition. Some of the assumptions, used inherently for theimulation are as under:

. The vehicle is comparatively small in breadth and length andhence the MV-SV surfaces, with their big radii, are effectivelyflat.

. There is no friction acting on any of the joints of the mechanism.

. There is no lining provided on the wheels and so the stainlesssteel wheel directly touches the walls.

. The rotational freedom of the wheels 6 and 7 has been arrestedfor static analysis.

Fig. 10. Minimum force requirement

tage of the device.

5. Contact stiffness between the wheels and the walls is taken as108 N/m, and the damping coefficient is assumed to be 1% ofcontact stiffness.

6. Static and dynamic co-efficient of friction are 0.3 and 0.2, respec-tively.

A) Static equilibrium reactions on wheelThe simulation is run for duration of 0.1 s. The device is not

free to move in vertical (X, gravity) direction for the first 0.04 sof the run. Thereafter, constraint is removed and gravity isaffected, in the simulation, for the remainder of the duration

(Fig. 11).

A constant actuation of 3300 N force on each piston is appliedby means of a double piston pneumatic actuator, and the mech-anism starts expanding between MV-SV (Y direction). As shown

s on pistons for static stability.

A.P. Singh et al. / Nuclear Engineering and Design 241 (2011) 3719– 3728 3725

Fig. 11. The device configuration at the start of the simulation.Fig. 14. Wheels 5 and 8 touch the safety vessel surface.

As soon as all the wheels in main vessel side make contactwith the surface, mechanism starts to expand on the SV side

Fig. 12. Wheels 1 and 4 touch the main vessel surface.

in the simplified view of the mechanism, the centre of gravityis eccentric in the positive Y direction because of the placementof the traction motors and steering motors arrangements. Dueto this, the wheels (wheels 1, 2, 3, 4) on the main vessel sidemove faster in comparison to wheels (wheels 5, 6, 7, 8) on thesafety vessel side.

The first contact takes place at time 0.0105 s on wheels 1and 4, because they are already offset by an extra 17 mm

by the spring arrangement with respect to middle wheels(Figs. 12 and 13).

Fig. 13. Reaction forces of the wheels 1

Fig. 15. Wheels 2 and 3 touch the main vessel surface.

Subsequent to this contact, wheels (5, 6, 7, 8) on the safetyvessel side move relatively faster and the next contact is madeon wheels 5 and 8 at 0.0148 s (Figs. 13 and 14).

After all the end wheels have made contact, the mechanismexpands farther in MV direction to adjust itself with a stablereaction force resulting in another contact by wheels 2 and 3on MV side at time 0.0165 s (Figs. 15 and 16).

and at t = 0.0242 s wheels 6 and 7 (traction wheels) also makethe contact with the SV (Figs. 16 and 17).

, 4, 5 and 8 during the simulation.

3726 A.P. Singh et al. / Nuclear Engineering and Design 241 (2011) 3719– 3728

Fig. 16. Reaction forces of the wheels 2

Fig. 17. Wheels 6 and 7 touch the safety vessel surface.

Fig. 18. Wheels 6 and 7 – positions, velocity and

, 3, 6 and 7 during the simulation.

At t = 0.0242 s all the wheels are in contact with the surfaceand pushing against the vessels to attain static equilibrium.

From t = 0.04 s to t = 0.1 s, X direction gravity is activated in thesimulation to check the stability of the device against gravity.The simulation shows all the wheels are in stable condition anddevice is in static equilibrium. The equilibrium reactions on thewheels are also depicted in the figures.

(B) Vehicle motion against gravityThe simulation is run for duration of 0.1 s. A constant actu-

ation of 3300 N force on each piston is applied by means of adouble piston pneumatic actuator. Device is not free to movein X (gravity) direction for the first 0.04 s of the run. Thereafter,the constraint is removed, so gravity is affected and torque ofvalue −9.25 N m (along Z-axis) is applied on wheels 6 and 7, inthe simulation, for the remainder of the duration.

As simulation shows after 0.0248 s, all the wheels are alwaysin contact with the surface and pushing against the vessels toattain static equilibrium. Up to 0.4 s there is no relative motionbetween the wheels and vessel. After 0.4 s the vehicle is free

acceleration profile with respect to time.

A.P. Singh et al. / Nuclear Engineering and Design 241 (2011) 3719– 3728 3727

Fig. 19. End wheel spring deformation with respect to time.

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Fig. 20. The future ISI device negotiati

to move in X direction and a torque of value −9.25 N m (alongZ-axis) is applied at wheel 6 and 7. This makes the device move,without slipping in negative X direction, resulting in the devicemotion against gravity (Ref. Fig. 18).

At the end of 0.1 s, acceleration of the vehicle is asymptotictowards 1.0 m/s2.

C) Simulation for vehicle motion against gravity in knuckle regionThe device motion is simulated to verify its maneuverability

in the cylindrical-knuckle transition region. Simulation is runfor duration of 0.1 s with the vehicle in an inclined position(25◦ with vertical) in knuckle region. Actuation force on pistonsand applied torque at wheel 6 and 7 are same as in previoussimulation, namely 3300 N and −9.25 N m, respectively.

The device is not free to move in X (gravity) direction for thefirst 0.04 s of the run. Thereafter, the constraint is removed and

the torque (along Z-axis) is applied at wheel 6 and wheel 7, inthe simulation, for the remainder of the duration (0.06 s.). Thedeformations of the end wheel springs are given in the Fig. 19,which ensure the wheel contact in the knuckle region.

cylindrical-knuckle transition region.

The simulation validates the inherent advantage of bringingall the wheels in continuous contact with the respective ves-sel surfaces to aid smooth motion of the device. The springscause these passive wheels to adapt to the geometry change asit moves and hence all the wheels remain pressed on to boththe vessel surfaces (Fig. 20).

5. Summary

The evolution of the ISI devices from prototype to PFBR hasgone through a rigorous analysis, simulation, experimental proto-types and validation in mock-ups. This has resulted in optimizingthe kinematic parameters for commercial FBRs. The device will be

manufactured and tested in a mock-up to validate the gap adapta-tion mechanism and key kinematic parameters of the device. Theseinputs are crucial for the designer to arrive at the size of the vesselsfor future FBRs.

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cknowledgements

The authors are grateful to S. Gopinath and M. Mohan Raj ofIRD, IGCAR and Dr. S.N. Shome of Central Mechanical Engineer-

ng Research Institute, Durgapur, India for their assistance in thectivities involving CAD modeling and simulation in the currentork.

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Seed, G., 1986. In-service inspection and monitoring of CDFR. Journal of NuclearEnergy 2.

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