CANDU 9 FUELLING MACHINE CARRIAGE D.J. Ullrich and J.F. Slavik · 2005. 2. 20. · CAN/CSA N285.0,...

FIRST INTERNATIONAL CONFERENCE ON CANDU FUEL HANDLING SYSTEMS, MAY 1996

CANDU 9 FUELLING MACHINE CARRIAGE

D.J. Ullrich and J.F. Slavik

AECL CANDUCANDU 9 Reactor and Fuel HandlingSaskatoon, Saskatchewan, Canada

CA9700730

ABSTRACT

Continuous, on-power refuelling is a key featureof all CANDU reactor designs and is essential tomaintaining high station capacity factors.

The concept of a fuelling machine carriage can betraced to the early CANDU designs, such as theDouglas Point Nuclear Generating Station. In theCANDU 9 480NU unit, the combination of a mobilecarriage and a proven fuelling machine headdesign comprises an effective means oftransporting fuel between the reactor and the fueltransfer ports. It is a suitable alternative to thefuelling machine bridge system that has beenutilized in the CANDU 6 reactor units.

The CANDU 9 480NU fuel handling systemsuccessfully combines features that meet theproject requirements with respect to fuellingperformance, functionality, seismic qualificationand the use of proven components. The designincorporates improvements based on experienceand applicable current technologies.

1. INTRODUCTION

CANDU reactor operation is based on the conceptof continuous, on-power fuelling, which is carriedout by the remotely controlled Fuel HandlingSystem. The fuelling machine head, a pressurevessel which contains new or irradiated fuel duringits transport between the reactor and the transferports, can be supported either by a bridge system,such as that used in the CANDU 6, or by a mobilecarriage such as in Douglas Point NGS. For theCANDU 9 480NU design, a carriage system hasbeen adopted.

An important consideration in the selection of thecarriage system for CANDU 9 was having a designthat would lend itself to seismic qualification forfuture sites with potentially higher seismicities thanthose of the previously constructed CANDUstations. Other design goals included reduced

construction time and improved on-powermaintainability of the carriage and the fuellingmachine head. Simplicity and the maximum use ofstandard, commercially available componentswere also a part of the design intent. Supplier andoperator input was incorporated.

In the following sections, an outline of therequirements applied to the fuelling machinecarriage concept is provided, along with a detaileddescription of the carriage system functional andstructural design. A summary of the benefits of thecarriage system is included.

2. DESIGN REQUIREMENTS

The key CANDU 9 480NU project requirements,related to the fuelling machine carriage systemperformance and functionality, included:

i) meeting the fuelling demands of the CANDU 9480NU reactor in support of the target lifetimecapacity factor of 90%;

ii) access, with the required positioning accuracy,to all fuel channels, the new and irradiated fueltransfer ports, the rehearsal facility and theancillary port;

iii) drive mechanisms compatible with computercontrol in the fully automatic, semi automatic andmanual modes;

Design requirements related to safety andlicensing were:

iv) meeting the requirements of the CAN/CSAN285 series of standards for Class 1C pressureboundary component supports, with references tothe ASME Boiler and Pressure Vessel Code,Section III, Subsection NF;

v) application of quality assurance programsduring design and construction, based on the CSACAN3-N286 and Z299 standards;

vi) carriage design licensable in Canada;

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vii) seismic qualification to ensure structuralintegrity during a 0.2 g Design Base Earthquake(DBE);

viii) providing safe and reliable transport of thefuelling machine head, thus ensuring the integrityof the contained new and irradiated fuel and of theinterfacing components;

ix) meeting the environmental qualificationrequirements for normal operating conditions andpostulated accident conditions;

x) satisfying the current human factorsrequirements with respect to the system layout,equipment maintenance and overall minimizationof dose expenditures;

Other requirements:

xi) minimizing construction time.

3. CARRIAGE SYSTEM DESIGN

The design of the CANDU 9 480NU carriage isfunctionally based upon the Douglas Point NGScarriage. There are two dedicated fuelling machineand carriage assemblies per reactor that operate inconcert to fuel a single channel. Correspondingly,there are two independent fuel transfer systems tohandle new and irradiated fuel.

Each CANDU 9 480NU carriage (Figure 1)operates between the fuel transfer ports inside themaintenance lock and the fuelling machine vault.Once in the vault, the carriage turntable rotates 90°so that the fuelling machine faces the reactor. Thecarriage positions the fuelling machine head at theselected lattice location in the X (lateral) and Y(vertical) directions, engages the seismic lockingmechanisms, and then advances the fuellingmachine head in the Z direction. Once the headarrives at the pre-stop position, X and Y correctionmeasurements are established. If necessary, thehead is retracted clear of the end fitting and X andY homing corrections are carried out by the fine Xand carriage Y drives, respectively. Therepositioned fuelling machine is then advanced tocontact the end fitting with sufficient force to stallthe Z drive. At this point, a standard CANDUfuelling sequence commences.

The carriage is designed to the requirements of theCAN/CSA N285.0, General Requirements ForPressure Retaining Systems and Components inCANDU Nuclear Power Plants and CAN/CSAN285.2, Requirements for Class 1C. 2C. and 3CPressure Retaining Components and Supports inCANDU Nuclear Power Plants. These standardsrecognize the unique design of CANDU fuel

handling systems and allow pressure vesselsupports such as the carriage to be designed inaccordance with the ASME Boiler and PressureVessel Code. Section III. Subsection NF. Throughconformance to these design standards andcodes, the carriage system becomes eligible forlicensing in Canada.

The carriage assembly structure consists of sixmain sub-assemblies: the base, turntable,columns, outer elevator, inner elevator, and guideplate (Figure 1). The movements of the carriagesub-assemblies relative to one another and withrespect to fixed supports facilitate the fuellingmachine positioning at the reactor. The fixedsupports consist of a floor rail and an upper guidebeam. The carriage rail runs parallel to the reactorface and into the fuelling machine maintenancelock. The upper guide beam is centered over therail, spanning its full length. The guide beamsupports the carriage structure in the Z direction bytrapping the guide plate within a slot in the bottomof the guide beam.

The base is a structure on two wheels that providesthe X motion and half of the rotation freedom of thecarriage. It is a welded assembly consisting of twobeams, internal bracing and a circular skirt. Thebeams run parallel to the rail with cross membersspanning the rail. Additional bracing, perpendicularto the main members, supports the skirt. Onewheel of the base is driven by an electric motorthrough a reduction gear train, while the secondwheel is an idler that, when required, can be drivenby the backup X drive. The base is guided alongthe rail by guide rollers that contact the outsideedges of the rail. Hold down hooks, that run in slotsin the sides of the rail and are bolted to the mainbeams, prevent lifting of the carriage during anearthquake. The skirt supports a mounting ring atthe top and four outriggers at the bottom. Theoutriggers are provided for construction andmaintenance purposes and are capable ofsupporting the carriage assembly independentlyof the wheels. Finally, the inner race of a slewingring is bolted to the mounting ring at the top of theskirt.

On top of the base, the outer race of the slewingring is bolted to the underside of the turntable. Theouter race is manufactured with an external gearcut in its outside perimeter. For carriage rotation,this gear meshes with a pinion fixed to the basethrough another reducer and an electric motor.The turntable structure is of a welded, sandwichstyle construction. It has internal cross-bracingthat runs diagonally between the main membersand it is enclosed on top and bottom with steel

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plates. Access openings are provided for theconstruction of the turntable, and for inspectionand replacement of the bolts between the innerslewing ring cage and the base.

The column sub-assembly is bolted to the top ofthe turntable and it consists of two vertical columnsand two horizontal crossbeams (Figure 2). Thevertical columns are internally braced and have Yguide tracks along their front and back sides. Theinternal bracing at the bottom of the columns is inan X pattern facing upwards, providing hightorsional rigidity. The bracing in the active portionof the columns is arranged in a zig-zag pattern withthe edges of each brace corresponding to areactor lattice position. These angled bracessupport loads imparted by the outer elevator Yguide bearings to the columns through the Y guidetracks. The top outside stub of each columnhouses a radial thrust bearing which holds theballscrew. The lower stub on each columnsupports the ballscrew tensioner, while the Y driveseismic brake and gear reducer are bolted to theoutsides of the columns below the stubs. The Ydrive electric motors and drive trains are mountedon the turntable for improved access. The lowerhorizontal crossbeam between the two columnsserves as a mechanical lower stop position for theouter elevator. Permanent shielding is bolted to thelower crossbeam that will shield the underside ofthe fuelling machine head magazine duringmaintenance. The upper crossbeam houses thebearings which in turn hold the shaft of the upperguide plate. These bearings provide a pivot pointto allow rotation of the turntable and the columnsrelative to the base and the upper guide beam. Themating surfaces between the upper crossbeamand the columns are provided with keys that limitseismic shear loads through the bolts.

The outer elevator is positioned between thecolumns and allows the vertical movement of thefuelling machine. The outer elevator consists of aframe, four pedestals, outer crossbeams, a Z drivemounting beam and Z drive tracks (Figure 3). Theframe fits between the columns with extensions onthe sides of the frame protruding ahead of andbehind each column. The pedestals are bolted tothese extensions and they house the Y guidebearings. The Y guide bearings provide support tothe outer elevator in both the X and Z directions byriding along both the face and sides of the Y guidetracks mounted on the columns. An outercrossbeam spans between the front and backpedestals along the outside of each column,thereby surrounding each column. This outercrossbeam is the mounting point for the Y drive

ballnut. The Z drive mounting beam bolts acrossthe back two pedestals and serves to transfer Zdrive reaction and seismic forces from the fuellingmachine to the columns through the pedestals andY guide bearings. The Z drive tracks are mountedon the bed of the outer elevator and provide a trackfor the inner elevator to ride along. The Z drive is anAcme screw which is turned by an electric motorthrough a reducer. The screw, while rotating, drivesan Acme nut along its length. The nut itself is fixedto one end of a seismic spring pack which in turnis fixed to the inner elevator. The spring pack iscomprised of a tuned stack of hard Belleville springwashers. Its purpose is to allow relative movementof the fuelling machine with respect to the carriage,thereby limiting the carriage seismic inertial forcesimparted to the end fitting should the fuellingmachine be clamped on to an end fitting during anearthquake.

The inner elevator moves relative to the outerelevator to provide the Z motion of the carriage.The inner elevator consists of a base, a yawturntable, and a cradle support. The base haslinear guide bearings along the bottom that run onthe top and sides of the Z tracks. The yaw turntableis a smaller slewing ring that has its inner racebolted to the top of the inner elevator base, and itsouter race bolted into the bottom plate adjoiningthe cradle support pillars. The support pillarshouse the pitch pivot trunnions of the fuellingmachine cradle and the cradle moves laterallywithin the support pillars to provide the fine Xmotion. Spring centering mechanisms betweenthe fuelling machine cradle and the cradle supportpillars, and between the cradle support and theinner elevator base provide the pitch and yawfreedom necessary to allow a fuelling machine tocenter over an end fitting.

4. SEISMIC DESIGN FEATURES

Undesirable motion of the CANDU 9 480NUcarriage under seismic conditions is preventedthrough several means. The first restraintmechanism is an arrangement of wedge and pinstyle seismic locks (Figure 4). When activated,these mechanical devices prevent rotation andtranslation by locking the carriage sub-assembliesto one another or to fixed supports. The seismiclocks are engaged during every channel refuellingsequence, prior to the fuelling machine beingadvanced over the end fitting. Both types of locksemploy electric motors and Acme screw drives,and readily accessible manual drives for recoveryoperations are available.

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The wedge style seismic locks accommodatethermal expansion between interfacingsub-assemblies and/or fixed supports. The locksemploy force control feedback through the Acmescrew drives to limit the depth of lock engagement.The force control establishes a positive contactbetween the locking wedge face and the lockingstriker plate but it limits the force in order to preventany tendency of the lock system to move thecarriage. The lower arrangement consists of twolocks bolted back to back and mounted at thereactor side of the carriage base. These two locksthen engage locking holes in a floor embedment.At the top of the carriage, one lock is bolted to theback of each column and it engages acorresponding hole in the upper guide beam. Thelocking holes in the upper guide beam and floorplate are spaced one lattice pitch apart. Due to thevarious angles at which the carriage must operatein the fuelling machine maintenance lock, a radialpattern of locking holes exists in that section of theupper guide beam. Because the base does notrotate, only a single embedment with two lockingholes is sufficient to lock the base to the floor whenthe carriage is in the maintenance lock.

The locking of the turntable to the carriage base isaccomplished with a straight pin style seismic lock.The straight pin style is used only in this locationbecause the two sub-assemblies, given theirphysical proximity, will be subject to the samethermal transients, thus leading to minimalmisalignment. One lock is located at the base ofeach column. The pin extends through the bottomof the turntable and engages a mating hole in alocking ring welded to the base structure within theslewing ring.

In addition to the wedge and pin type seismiclocks, all electric drive motors have integral brakeswhich are automatically applied when the drive isde-energized, making them fail-safe. For furthersafety, the ballscrews are equipped withseismically qualified fail-safe brakes and arepre-tensioned with spring packs that preventcompression of the ballscrew under seismicallyinduced lifting loads.

In order to protect the fuelling machine carriageassembly from an earthquake occurring while thecarriage is in transit, a seismically activated andqualified switch will cut the power to all drives,thereby activating their brakes. As a backup to themotor brakes, seismically qualified snubbers andmechanical stops prevent overtravel and providefor controlled deceleration of any componentshould the motor brakes slip.

5. DESIGN BENEFITS

The benefits of the carriage design range fromsimplified construction to improved reliability andreduced time and radiation dose expendituresduring operation and maintenance activities. Thenew design incorporates feedback from operatorsand suppliers. The CANDU 9 480NU design is alsoexpected to be adaptable for CANDU sites withseismic levels higher than the 0.2 g DBE currentlybeing considered.

Manufacturing tolerances are eased by the use ofshims between sub-assemblies becausecustomized shims bring critical sub-assembliesinto alignment. Along with these shims, simplebolted connections between sub-assemblies allowfor a shorter carriage set up time at site.Procurement, manufacturing and construction ofthe carriage are all simplified by maximizing theuse of standard commercial parts. Additionally, theselection of proven electric motors as the primemovers has led to a significant reduction in thenumber of mechanical parts required for theCANDU 9 carriage in comparison to the CANDU 6carriage, largely due to the elimination of thecarriage oil hydraulic system.

The reliability of the CANDU 9 carriage is expectedto be improved over that of the CANDU 6 carriage.The structure is inherently robust, with all carriagecomponents that support the fuelling machinebeing designed to accommodate loads resultingfrom a DBE. Given that the normal operating loadsare, typically, an order of magnitude lower thanseismic loads, the mechanical equipment of thecarriage is expected to have considerableoperating lifespan. In order to further improve thesystem reliability, a backup X drive is provided anda single Y drive unit can safely lower the elevatorand fuelling machine head assembly. As well, oneseismic brake and one ballscrew can support theentire suspended mass. Other features thatenhance safety and reliability include an increasedZ drive range for recovery purposes; if required,the full Z drive range will allow the recovery of afuelling machine with a guide sleeve stuck in thesnout, even with a crept pressure tube.

Maintenance activities, and the anticipatedradiation dose expenditures attributable to theseactivities, were a significant consideration in theselection of a carriage system. The CANDU 9480NU mobile carriage system allows for carriagemaintenance to be carried out inside the shieldedand environmentally isolated maintenance locks,rather than in more active locations such as thefuelling machine vaults. On-power maintenance

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of the carriage is possible, a feature that positivelycontributes to the station capacity factor ascarriage maintenance does not require a reactorshutdown. Other improvements are obtainedthrough ready access to carriage components andthe use of bolted component connections. Boltedconnections facilitate the removal ofsub-assemblies that can then be taken to lowactivity locations for maintenance. For field work,strategically placed shielding for the fuellingmachine head will be incorporated into thecarriage structure so that fuelling machine headmaintenance can be carried out with less dosecommitment than in the previous CANDU designs.Finally, through the use of commercially availableparts, carriage maintenance can be performed byless specialized work groups, thus enabling doseequalization programs to succeed.

6. SUMMARYThe CANDU 9 480NU fuelling machine carriagedesign represents a departure from the bridgesystem utilized in the successful CANDU 6 reactordesign. The carriage concept is not new, however,as its origins can be traced to the earlier CANDUreactor designs such as that at Douglas PointNuclear Generating Station.

The two wheel fuelling machine carriage design,described in the foregoing sections, meets thefunctional, performance, safety and constructabilityrequirements of the CANDU 9 480NU project. Thecombination of a robust CANDU 9 carriage, fullyintegrated with the proven CANDU 6 fuellingmachine head, has the capacity to support thestation lifetime target capacity factor of 90%.

The carriage design has the potential to satisfy therequirements of future CANDU sites with higherthan 0.2 g DBE levels. Other significant benefitsinclude on-power maintenance access to boththe carriage and the fuelling machine head, andthe use of commercially available, standardizedcomponents. These features are intended tominimize dose expenditures and the costsassociated with fuel handling systemmaintenance. In addition, a high degree ofpre-assembly is planned in order to shortenin-situ construction and the commissioning timerequirements.

The carriage system, as a pressure boundarycomponent support, meets the requirements ofthe applicable CSA standards and ASME Coderequirements. It is designed to be licensable inCanada, as well as other comparable internationaljurisdictions.

ACRONYMS

CANDU - Canada Deuterium Ujanium

ASME - the American Society of MechanicalEngineers

CAN/CSA - Canada / Canadian StandardsAssociation

DBE - Design Basis Earthquake

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GUOEBEAM

M E PLATE

COLUMN

FUELLNG MACHNECRADLE

OUTERELEVATOR

NNERELEVATOR

TURNTABLE

BASE

FIGURE I CARRIAGE GENERAL ARRANGEMENT

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UPPER SOSMCLOCKS (2)

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LOWERCROSSBEAM

TURNTABLESBSME LOOS (2)

UPPEREROSSBEAM

LOWER SEISMCLOCKS Gl

FIGURE 2 CARRIAGE COMPONENTS

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NNERCROSSBEAMS C l

Z - QRIVEMOUNTING BEAM

OUTERCROSSBEAMS 12)

CRADLEPILLARS

YAWTURNTABLE

BALLNUTS (2)

Y - GUDE BEARINGHOLDERS

PEDESTALS IM TRACKS 0

FIGURE 3 ELEVATOR COMPONENTS

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WEDGE - STYLESEISMIC LOCK

PIN - STYLESEISMIC LOCK

FIGURE 4 SEISMIC LOCKING MECHANISMS

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THE CANDU 9 FUEL TRANSFER SYSTEM

Z.G. KeszthelyiGE Canada, Nuclear Products

107 Park Street NorthPeterborough, Ontario, K9J 7B5

D.T. MorikawaAECL

2251 Speakman DriveMississauga, Ontario, L5K 1B2

CA9700731

ABSTRACT

The CANDU 9 fuel transfer system isbased on the CANDU 6 and the OntarioHydro Darlington NGD designs, modifiedto suit the CANDU 9 requirements. TheCANDU 9 new fuel transfer system isvery similar to the CANDU 6, withmodifications to allow new fuel loadingfrom outside containment, similar toDarlington. The CANDU 9 irradiated fueltransfer system is based on the Darlingtonirradiated fuel transfer system, withmodifications to meet the more stringentcontainment requirements, improveperformance, and match station layout.

1. INTRODUCTION

The CANDU system is based on on-powerfuelling. An important aspect of thesystem is 'fuel transfer' which includes ailthe equipment and operations required toload new fuel into a fuelling machine fordelivery to the reactor and later totransfer the irradiated fuel between afuelling machine and the storage bay.

This paper describes an advanced fueltransfer system being designed for theCANDU 9.

CANDU 9 is the latest version of thePressurized Heavy Water Reactor (PHWR)system developed in Canada by AECL. Ithas a net electrical output in the range of870 MW.

The seemingly simple fuel transfer systemmust satisfy many stringent requirements.The basic ground rules for this equipment

are safety and reliability. The equipmentmust be designed and built, for instance,in such a way that at no time will theoperator be confronted with a situationwhich leaves him without any means forsolving a break-down problem involving astuck, uncooled fuel bundle in theirradiated fuel port.

The paper provides a brief description andillustration of the new and irradiated fueltransfer systems at both the CANDU 6and Darlington stations. The papercontinues with a more detailed descriptionof the proposed CANDU 9 fuel transfersystem which is being designed by a jointteam of AECL and GE Canada designers.

2. DESCRIPTION OF NEW FUELTRANSFER SYSTEMS

2.1 CANDU 6

In the CANDU 6 stations, new fuel isstored outside the reactor building anddelivered into the reactor building whenneeded. Once in the reactor building,new fuel is loaded manually into the newfuel transfer mechanism. It is thentransferred into the fuelling machine headunder remote control from the maincontrol room. (See Figure 1).

Two new fuel transfer mechanisms areprovided; one to supply each fuellingmachine head.

The new fuel transfer mechanisms arelocated in the reactor building, withincontainment, between the two fuellingmachine locks.

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The new fuel transfer mechanism consistsof a loading trough and ram, a magazineand indexing drive, a single-stage transferram, and a port/magazine transition piece.

The magazine assembly consists of ahousing and rotor, with capacity for 12fuel bundles and the new fuel port shieldplug. The magazine is indexed by anelectric motor and a mechanical indexingunit.

An airlock gate valve is installed betweenthe new fuel magazine and the loadingtrough to seal off the magazine wheneverfuel is not being loaded into themagazine. This valve reduces the spreadof contamination from the fuellingmachine maintenance lock into the newfuel room. Contamination is also reducedthrough a duct connected to the vapourrecovery system which maintains a slightnegative pressure in the new fuelmagazine.

The loading ram is an oil/air driven ram.The transfer ram is driven by an electricmotor and chain drive.

The port/magazine adapter connects themagazine and the new fuel port. Thisassembly locks the new fuel port shieldplug in place and releases the shield plugfrom the transfer ram when needed.

The new fuel ports are mounted inembedments in the maintenance lockwalls. A shield plug is normally latchedin the new fuel port to provide shieldingfor the new fuel room.

2.2 DARLINGTON

There are four new fuel transfermechanisms in each of the two loadingareas. These mechanisms are locateddirectly above the irradiated fuel receptionbay in the fuelling facilities auxiliary areas.(See Figure 2).

The new fuel port penetrates thecontainment wall between the new fuelloading area and the fuelling machineroom. The containment integrity is

maintained by two gate valves betweenthe new fuel port and the magazineassembly. A third gate valve is locatedbetween the loading trough and themagazine and is interlocked with theother gate valves to prevent simultaneousopening. The magazine is maintained at aslightly negative pressure through anactive vent to prevent any flow of tritiuminto the new fuel loading area.

The fuel bundles are transferred from theloading trough into the magazine by aram, the force of which is restricted tolimit the force applied to the bundles.

The fuel bundles are transferred from themagazine into a transporter located in thenew fuel port and then into the fuellingmachine head by a two-stage ram. Thetransporter is moved from the new fuelport into the head by one ram while thesecond ram transfers the bundles fromthe transporter into the fuel carriers in thefuelling machine head magazine.

2.3 CANDU 9

The CANDU 9 new fuel transfermechanism is based on both the CANDU6 and Darlington designs. The designpermits new fuel to be loaded into thefuelling machine head from outsidecontainment.

The CANDU 9 design uses the standard37-element fuel bundle, but will also beable to accommodate the 43-elementCANFLEX fuel bundles in the future. Thefuel handling sequence for CANDU 9 isillustrated in Figure 4.

2.3.1 Description

Two new fuel transfer mechanisms areprovided; one to supply each fuellingmachine head.

The mechanisms, shown in Figure 5, arelocated outside containment in the reactorauxiliary building on either side of theairlock. New fuel is therefore loaded intothe new fuel transfer mechanisms fromoutside the reactor building.

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The new fuel transfer mechanism consistsof a loading trough and ram, a magazineand indexing drive, a single-stage transferram, a port and two port containmentvalves.

The new fuel magazine, similar to theCANDU 6 magazine, consists of acompletely enclosed steel housing with arotor. As in CANDU 6, there are six fuelstations and a station for the port shieldplug. The magazine rotor is driven from anelectric motor through a pinion and bevelgear. Indexing is controlled by amechanical cam and roller drive indexingunit.

The fuel loading ram consists of astainless steel rack with a ram headassembly. The ram is driven by a pinionand brushless servo motor.

An airlock valve, installed between thenew fuel magazine and the loadingtrough, seals off the magazine wheneverfuel is not being loaded into themagazine. This valve reduces the spreadof tritium through the new fuel magazineinto the new fuel room and enables thetransfer mechanism and fuelling machinehead to be pressurized during fuel transferto the fuelling machine head.

The transfer ram is similar to the new fuelloading ram and consists of a ram tubewith a latching ram head and a stainlesssteel rack. The entire ram is contained ina housing with a seal at the magazinehousing. The ram is driven by a pinionwith a sealed shaft.

The new fuel port is similar to the CANDU6 component. This assembly locks thenew fuel port shield plug in place andreleases the transfer ram from the shieldplug when needed.

The shield plug is normally latched in thenew fuel port and performs the samefunction as on CANDU 6.

The new fuel port is mounted in anembedment in the reactor building wall

between the new fuel transfer room andthe fuelling machine lock. Because thenew fuel transfer mechanism is fixed tothe reactor auxiliary building, and theports to the reactor building, the transfermechanism is designed to accommodatedifferential settlement and building shiftsdue to seismic events.

The port containment valves are locatedbetween the port and the magazinehousing. These valves are normallyclosed to maintain the containmentboundary.

2.3.2 Operation

New fuel pallets are delivered from thenew fuel storage room to the airlocklevel, and from there to the new fueltransfer room.

The new fuel bundles are inspectedbefore loading into the transfermechanism. The fuel bundles are liftedfrom the pallet using a fuel bundle liftingtool, suspended from an air balance hoistand a monorail. The bundles are placedon an inspection table and checked forinterlocked element spacers, using agauge, and vacuumed/air blown ifneeded.

Two bundles are loaded into the loadingtrough and the trough lid is closed. Theairlock valve is opened and the bundlesare pushed into the magazine by the newfuel loading ram. The ram is retractedand the magazine is indexed to the nextchannel position and two more bundlesare loaded. This is repeated until themagazine contains the required number ofbundles.

During new fuel loading, the magazine isopened to the ventilation - system tomaintain air flow from the new fuelloading room into the magazine.

To transfer fuel from the new fuel transfermechanism into the fuelling machine, thefuelling machine clamps onto the new fuelport in the fuelling machine lock, withincontainment in the reactor building. The

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water level in the fuelling machine islowered and the fuelling machine preparesthe port for fuel transfer by installing theguide sleeve.

The new fuel transfer mechanism and thefuelling machine head are pressurized andthe two port containment valves areopened. During the remainder of thetransfer sequence, the pressure in thetransfer mechanism and port is controlledby the new fuel transfer mechanismauxiliaries.

Until the containment valves are opened,the port and containment valves are thecontainment boundary and rest of thenew fuel transfer mechanism is outsidecontainment. After the containmentvalves are opened, the fuelling machinehead becomes the containment boundary.The pressure in the transfer mechanismand head allow containment integrity tobe confirmed and monitored.

To meet the regulatory requirements, thenew fuel port and containment valves areClass 2, and the remainder of the transfermechanism is Class 6.

Fuel bundles are transferred from thetransfer mechanism into the fuellingmachine head by the transfer ram. Thetransfer ram first removes the port shieldplug and stores it in the new fuelmagazine. The ram then pushes the fuelbundles in pairs from the new fuelmagazine into the fuelling machine head.This operation is controlled remotely fromthe fuel handling console in the maincontrol room.

3. DESCRIPTION OF IRRADIATED FUELTRANSFER SYSTEMS

A paper presented at an earlierconference (1) defined the major designrequirements for irradiated fuel transfersystems.

3.1 CANDU 6

The CANDU 6 irradiated fuel handlingsystem consists of discharge and transferequipment in the reactor building, andirradiated fuel reception and storage baysand equipment in the service building.(See Figure 1).

Irradiated fuel is transferred from thefuelling machine head to the dischargebay in air. The fuelling machine clampsonto the irradiated fuel port, prepares theport for transfer, and lowers the waterlevel in the head. The two ball valves onthe irradiated fuel port are opened andbundle pairs are pushed by the fuellingmachine ram through the port and ontoan elevator.

The elevator lowers the bundles into thedischarge bay onto a conveyor cart, thenreturns to the port to receive the nextbundle pair. This is repeated until all fuelhas been discharged from the fuellingmachine. There is one discharge bayconveyor serving both fuelling machines.The discharge conveyor transfers the cartto the reception bay conveyor.

During irradiated fuel transfer from thefuelling machine head, the containmentboundary is at a containment gate at theend of the discharge bay canal. EarlierCANDU 6 units were not equipped with acontainment gate and rely on the fuellingmachine auxiliaries and the head of waterin the discharge canal for the containmentboundary. At all other times, the portvalves are closed.

After fuel reaches the reception bay, thefuel rack is removed from the conveyorcart and placed in the reception bay. Fuelbundles are transferred to the storage baytrays using manual tools. Once the traysare full (24 bundles/tray), they aretransferred to the storage bay and placedon storage tray supports.

The storage bay trays are stacked 19 highand sets of four stacks are secured with acovering frame. This assembly is sealedwith an IAEA device.

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For interim dry storage, bundles aretransferred from the trays to cylindricalbaskets. The baskets are then placed indry storage concrete canisters.

3.2 DARLINGTON

The major differences between theCANDU 6 and Darlington systems are asfollows:

The CANDU 6 irradiated fuel transfersystem is 'above water' meaning that theirradiated fuel port is located above thewater level in the bay. Darlington uses an'underwater' concept wherein the port islocated below the bay water elevation.An air-filled transfer chamber ('airchamber') is used. The bundles aretransferred from D20 in the fuellingmachine head, to the air chamber, andfinally into H20 in the bay. In a CANDU 6storage bay, irradiated fuel is stored insingle-layer trays. In Darlington, it isstored in multi-layer modules. Thisintroduces an additional indexingoperation.

A description of the Darlington systemfollows. Figure 3 illustrates the systemfeatures.

The irradiated fuel port penetrates thecontainment wall 4.4 m below the surfaceof the bay water. An underwater airchamber is attached to the port from thebay side. Flooding the air chamber withbay water provides emergency cooling incase a bundle becomes stuck in the port.Defected fuel in the underwater chambercan be identified by drawing air from thechamber through a detector ('drysniffing').Irradiated fuel is discharged from thefuelling machine onto a shuttle in theirradiated fuel port. The shuttle isretracted through the port into the airchamber where it is supported on a ladle.The ladle and shuttle are lowered totransfer the shuttle onto a verticallytravelling elevator. The elevator islowered to align the shuttle with a chosentube of the module, and the fuel ispushed out of the shuttle into the module.

Horizontal indexing of the modulecombined with vertical indexing of theelevator make it possible to fill all tubes inthe module.

Accurate indexing of the module conveyoris obtained by a Geneva mechanism. Atelescopic water hydraulic cylinderprovides smooth motion of the shuttlethrough the port. Shuttle positiondetection is by ferromagnetic sensors.Underwater equipment is driven, as far aspossible, from above water by motorizeddrives. All motorized equipment has thecapability of being driven manually.

The initial concept for handling defectedfuel at Darlington was to separatedefected fuel from sound fuel and, afterinspection in the reception bay, place it incans. Later experience indicated that theisolation of defected fuel in cans andcontainers was not necessary. A decisionwas made to place defected fuel directlyinto modules, with provisions for laterremoval of defected fuel from themodules for inspection.

3.3 CANDU 9

The fuel handling sequence for CANDU 9is illustrated in Figure 4. The systemminimizes the fuelling machine refuellingcycle time. This is achieved bytemporarily storing the irradiated fuel inthe port. Loading of the fuel into thestorage bay takes place later, after thefuelling machine departs from theirradiated fuel port.

3.3.1 Description

The irradiated fuel transfer system, shownin Figure 6, is located primarily in thereactor auxiliary building. It consists of:

a) An irradiated fuel port mounted in thereactor building containment wall.

b) Two port containment valves.c) A flexible port/magazine transition

piece.d) A totally enclosed irradiated fuel

magazine and its drive assemblywhich is located in the storage bay

125


wall within the reactor auxiliarybuilding.

e) An irradiated fuel transfer ram anddrive.

f) A bay valve.g) Associated air and water auxiliary

systems.h) Storage bay equipment which

includes the indexing tray, storageram, bundle tilter, 'basket modules',stacking frames and handling tools.

A paper published earlier (2) describes the'basket module' and future considerationsfor the dry storage of CANDU fuel.

The irradiated fuel port assemblyconforms to Class 2, Class 4 and Class 6as appropriate. It has the flexibility andstrength requirements to permit thehoming and locking of the fuellingmachine and to withstand high seismicloads. The port is sloped down towardsthe port magazine. D2O carried from thehead on the fuel bundles is collected toprevent its loss to the bay.

The irradiated fuel transfer mechanismspans two separate buildings; the reactorbuilding and the reactor auxiliary building.These two buildings can moveindependently of one another undersettlement and seismic actions.

The fuelling machine unloads irradiatedfuel through its associated port whichleads to one of the irradiated fuel storagebays located outside the reactor buildingcontainment wall. Each face of thereactor has one storage bay dedicated toit. The two storage bays are notinterconnected.

The port/magazine transition pieceprovides the required flexibility betweenthe buildings to allow these movementsto be accommodated without loss ofcontainment. This is achieved using twospecially designed ball joints toaccommodate the vertical, horizontal andaxial displacements. The transition piecehas a D2O recovery circuit to recover D2Ovapour that evaporates or boils off thefuel bundle surface during fuel transfer in

air. This D2O recovery loop also containsprovisions for 'dry sniffing' to detectdefected fuel as it passes through thetransition piece.

The irradiated fuel magazine (or portmagazine) is located in a sleeve in thestorage bay wall within the reactorauxiliary building. The end plate of themagazine housing is removable to enablemaintenance to be carried out on therotor assembly. Mounted on the endplate are the transition piece, themagazine drive assembly, the irradiatedfuel transfer ram, and cooling waterconnections. The heat generated by theirradiated fuel bundles within themagazine is removed through a heatexchanger fitted internally in the magazinehousing.

The magazine rotor consists of astationary shaft, two end plates and sixmagazine channels. There are sevenchannel positions with one position usedduring maintenance only. This position isfitted with a hinged blanking plate toallow space for special tools (e.g.cleaning tools). The capacity of themagazine rotor is therefore six pairs offuel bundles.

The CANDU 9 irradiated fuel transfersystem is being designed to accommodateemergency recovery for all foreseeablefailure scenarios in a manner thatminimizes radiation and conventional riskto station staff, the public and theenvironment.

3.3.2 Operation

To prepare for fuel transfer, a pump isstarted to establish water circulation flowthrough the port magazine. The waterflows over a weir for level control in themagazine. The irradiated fuel magazineand transition piece are pressurized withair. The fuelling machine homes andlocks onto the irradiated fuel port and ispressurized. The two port containmentvalves are then opened and the port airpressure system regulates the pressure inboth the port and the head.

126


The fuelling machine magazine channel,containing the fuel bundles to betransferred, is aligned with the port. Therams of the fuelling machine are used topush the irradiated fuel from the fuellingmachine magazine into the port magazine,two bundles at a time. The rams are thenretracted into the fuelling machine andboth magazines index to the nextposition. This procedure is repeated untilall the fuel has been transferred.

The irradiated fuel transfer takes place inair from the time that the fuelling machinemagazine is indexed to align the fuel fortransfer until the port magazine is indexedfrom the load position and the fuel issubmerged below the water level in theport magazine. Fuel is then cooled in thecirculating water in the magazine.

The control systems associated with thedesign ensure that the proper sequencingof the operation is achieved. Once thefuel transfer is complete, the two portcontainment valves are closed. The portis then flooded. In an emergency, theport and magazine can be flooded from adump tank by gravity.

Irradiated fuel is now transferred from theport magazine to the storage bay byopening the bay valve. This operationequalizes the pressure in the port with thebay pressure. The bundles are pushed bythe transfer ram, two at a time, from themagazine onto an indexing tray as it ismoved automatically across the face ofthe irradiated fuel port. The tray has sixpositions for fuel bundles. Uponcompletion of transfer, the bay valve isclosed.

A storage ram is then used to push thebundles, one at a time, into a bundle tilterdesigned to rotate the bundle into thevertical position. The tilter restrains thebundle during this operation and is fittedwith a shock absorber to reduce impacton the bundle during tilting. A toolsupported from the manbridge is used totransfer the irradiated fuel bundles fromthe tilter to the 'basket module1.

4. CONCLUSION

Major features of the CANDU 9 irradiatedfuel transfer system design includecommonality of equipment between thenew fuel and irradiated fuel mechanismsand reuse or adaptation of technologyused and proven at other CANDU plants.The transfer system design providesadaptability to a wide range of siteconditions, low capital cost, shortconstruction schedule, minimum systemcomplexity, high system availability, lowoperating and maintenance cost, and ageneric approach where many of thefeatures can be applied to future CANDUdesigns.

ACKNOWLEDGMENTS

The authors would like to thank OntarioHydro, AECL and GE Canada for the useof their data.

REFERENCES

(1) KES2THELYI Z.G., DIDOMIZIO F.,GAERTNER B.R., "The Evolution ofCANDU Irradiated Fuel TransferSystems", A Paper Presented at theThird International Conference onCANDU Fuel, Chalk River, Ontario,Canada, 1992 October 4-8.

(2) NAKAGAWA R.K., "StandardizedApproach to the Design of CANDUUsed Fuel Receptacles", A PaperPresented at the Third InternationalConference on CANDU Fuel, ChalkRiver, Ontario, Canada, 1992October 4-8.

127

4ACCEPT

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CGFIGURE 6

CANDU 9 FUELLING MACHINE CARRIAGE D.J. Ullrich and J.F. Slavik · 2005. 2. 20. · CAN/CSA N285.0,...

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Transcript of CANDU 9 FUELLING MACHINE CARRIAGE D.J. Ullrich and J.F. Slavik · 2005. 2. 20. · CAN/CSA N285.0,...