Full Steam ahead for Flamanville 3EPR turbine island construction

POWER

May 2010

The 1750 MWe ARABELLE™ turbine generator is the world’s largest engine. The first such machine in Europe is

currently under construction at EDF’s Flamanville 3 site. The turbine island at Flamanville 3 has now

progressed from the manufacturing phase to construction, with the focus currently on site work and

installation of major components.

, Performance & Process Director, and ,Project Director, Flamanville 3, Alstom Power Thermal Products, Nuclear

s France’s first EPR, EDF’s 1750MWe Flamanville 3 unit, currentlyunder construction on the coast ofNormandy, marks the start of a new

era for the French nuclear programme – both interms of unit size and technology – the EPRbeing classified as a “Generation III” reactor,which is advanced but also evolutionary.Similarly, the turbine island is an evolutionarysolution that builds very firmly on experienceamassed with the country’s 58 existingpressurised water reactors and also withexported plants. Areva is providing theFlamanville 3 nuclear steam supply system,which is designed to provide over 9000 t/h ofsaturated steam at a pressure of 75 bar and atemperature of 290°C to the steam turbine.

Alstom’s role, under a contract awarded inSeptember 2006, is to convert this vast quantityof wet steam into electricity in the most effectiveway possible, achieving a thermal cycleefficiency in excess of 38%. The Alstom scopeof supply includes engineering, manufacturingand procurement, construction andcommissioning of the steam turbine,turbogenerator, condenser, moisture separatorreheaters, feedwater heaters, deaerator,condensate extraction pumps, cooling watercirculating pumps, plus auxiliary equipment suchas the turbine bypass system, compressed airdistribution system and busbars.

Alstom has in fact over the years provided thesteam turbines, turbogenerators, condensers andmoisture separator reheaters for all the Frenchoperating nuclear plants to date, and has alsosupplied a large proportion of the other mainequipment, such as circulating water pumps andcondensate extraction pumps, boiler feed waterpumps with associated drives, emergency dieselgenerators, etc.

But Flamanville 3, with a turbogenerator ratedat 2000 MVA, represents a significant scaling upover what has gone before, and indeed when itenters service, currently expected in 2012, it willbe the world’s largest power generating unit(although the Taishan 1 and 2 EPRs currentlyunder construction in China – and due to entercommercial service in 2013 – are also based onAlstom steam turbine technology and mightsubsequently take the lead by a short head due toa slightly higher reactor rating).

Flamanville 3 will incorporate the longest laststage blade ever made by Alstom.

Also, in a departure from previous FrenchPWR practice, it will use vertical moistureseparator reheaters, as specified by EDF in itsrequest for proposals.

The design of the 1750 MWe ARABELLE™steam turbine for Flamanville 3 builds onexperience with EDF’s four 1550 MWeARABELLE™ units currently operating inFrance. These machines, two each at the ChoozB and Civaux N4 plants, have been running forover ten years and already set the record for thelargest steam turbines in service.

The Arabelle concept, initially introduced atthe end of the eighties, was to deliver higherefficiency, reduced investment costs for theturbine hall, reduced maintenance, andmaximum reliability. With the support andencouragement of EDF, ARABELLE™ wasdeveloped at a time when most turbine

manufacturers were limiting their ambitions inthe face of bleak commercial prospects fornuclear power.

Unique among large nuclear steam turbines,the ARABELLE™ architecture employs singleflow HP and IP sections, contained in acombined HP/IP casing to reduce overall length(with, in the case of Flamanville 3, about 1100MWe produced from a 13 stage rotor weighingjust 140 t, in a HP/IP module weighing around

600 t). The combined HP/IP casing is similar tothose sometimes used in fossil firedapplications except for its much larger size(bearing in mind that a saturated nuclear steamturbine needs to accommodate an inlet volumeflow about five times bigger than a coal unit ofequivalent power because of the much lowersteam pressures and temperatures). In theARABELLE™ concept, the incoming mainsteam expands in the single flow HP section andis then fed to the moisture separator reheaters(MSRs), where it is superheated in two stages,using a derivation of the main steam and anextraction from the HP. The superheated steamis then expanded in the single flow IP cylinderof the turbine. This IP section is a keydistinguishing feature of ARABELLE™ (seediagram, bottom left).

Previous-generation nuclear steam turbinestypically have a two-flow HP turbine plus twoor three two-flow LP sections, in which the IPexpansion is accommodated. After expansion inthe HP turbine, the steam typically enters theMSRs, where it is dried and superheated by aderivation of the main steam and then fed to theLP turbines for final expansion down to thecondenser pressure. ARABELLE™ is the onlylarge nuclear turbine that has a separate singleflow IP section, with the steam flow split formultiple expansion in the LP sections done at apressure about three times lower than previousgeneration machines.

The maximal use of single flow expansion,from 75 bar down to 3 bar, accounting for 60%of the total expansion, is a major contributor tothe overall high efficiency. Single flow isinherently highly efficient because of thereduction in the effect of secondary losses thatdevelop at blade roots (eg due to turbulence)and tips (eg due to leakage) in the steam path.Basically, the significance of “border effects”is reduced because a greater proportion of theexpansion is achieved with longer blades,which have a higher aspect ratio (=height/width), see diagram below.

ARABELLE™ now comes in two sizes forboth 50 Hz and 60 Hz grids, a 1700 MWe classmachine and a 1000 MWe version. As well asbeing used at Flamanville 3, the 1700 MWeversion is to being deployed at Taishan 1 and2 in China (the latter employing a shorter laststage blade, with smaller LP exhaust area,reflecting warmer average cooling watertemperatures than in Normandy), and isselected for the EPR projects in the USA,starting with Calvert Cliffs 3. The 1000 MWeversion has been adopted by China for itsCPR1000 projects (an indigenised version of

the French-supplied Daya Bay 900 MWePWRs) under construction at: Ling Ao 3 and 4(Phase 2); Hongyanhe 1-4; Ningde 1-4;Fangjiashan 1 and 2; and Fuqing 1-4.

Also contributing to high efficiency is the largeLP exhaust area, 155 m2 at Flamanville 3, takingmaximum benefit of Alstom’s longest ever laststage blades (1.75 m).

The Alstom LSB design features an integralsnubber to ensure reliability and a curvilinear firtree attachment, providing easier access forinspection.

Thanks to the vibration control provided bythe snubber connection between blades, thistype of blade provides the benefit of a reducedweight – around 80 kg – compared with freestanding blades. To achieve the requiredstiffness free standing blades may end upweighing around four times more than this.With relatively light, integrally snubberedblades, it is possible to design the bearingsystem so that it can withstand the unbalancecreated by postulated failure of the LSB.Meeting this design criterion is not reallyfeasible with significantly heavier blades.

Aerodynamic design is also optimised andthe last stages benefit from the 3D profilesdeveloped by advanced computer modelling,

and now made possible by modernmanufacturing techniques.

The Flamanville site is fairly good in terms ofseawater cooling water temperature, with aresulting condenser pressure of 46 mbar. Thelarge LP exhaust area at Flamanville is designedto make maximum use of this by minimising thevelocity of the exhaust steam and thus the kineticenergy losses. Kinetic energy of the exhauststeam can represent several percentage points ofturbine power, and its reduction is highlybeneficial to the project.

Further significant performance benefits derivefrom the use of two-stage moisture separatorreheating, as well as from improvements to thefeedwater heating systems.

With the two-stage moisture separatorreheater, for a given final reheat temperature,only half the live steam flow is used comparedwith a single stage reheater. This replacementof main steam by already partly expanded HPextraction steam provides a very valuable cycleefficiency benefit. As already noted, the MSRsat Flamanville 3 are arranged vertically, adeparture from previous practice at FrenchPWRs, but an arrangement already provided onother units by Alstom, eg in Germany.

The feed heater configuration at Flamanville3 is upgraded compared with the previousgeneration of nuclear plants, and is in line withbest practice today. There are seven stages offeedwater heating: four LP heaters (fed fromextractions in the LP section, an extractionfrom the IP section, and the IP exhaust); thedeaerator (fed from HP exhaust); and two HPheaters (fed from extractions in the HP section).

This is one more stage of reheat than inprevious-generation plants. In addition,forward recovery pumping of condensate of LPheaters is used to significantly increase theplant net output. Both these modifications havea measurable impact on the plant output.

Use of welded rotors, as opposed to mono blocsolid rotors, is a well established feature ofAlstom turbines (both gas and steam), developedover the last 80 years.

The rotor is made up of smaller forgings. Forvery large rotors as required in nuclear turbines,it allows better control of material properties.Because of the reduced stress compared with theshrunk on disk design, steel with lower yieldstrength can be selected allowing better resistanceto stress corrosion cracking while achieving theproperties required for the disks supporting thelast stage blades. Ultra large forgings can be a verysignificant bottleneck in the supply chain fornuclear plant, whereas smaller forgings can besourced from a larger number of suppliers.

As already noted, the Flamanville turbineisland includes a number of features aimed atfacilitating maintenance. For example, the LPinner casings are independent of the LP exhausthoods, allowing LP turbine assembly to beindependent of the condenser and the shaft-lineto be aligned without exhaust hooddismantling. In addition having the IP/LP pipework below the turbine table improves accessfor LP module maintenance.

The separate IP expansion also bringsmaintenance benefits.

The Flamanville 3 turbogenerator is a GIGATOP4-pole machine, with hydrogen-cooling of thestator, rotor and the static parts and water-coolingof the stator winding. Features and benefits include:• Stainless-steel cooling tubes for direct cooling

of the stator bars. The corrosion resistance ofstainless steel avoids clogging of the coolingtubes, losses are minimised and efficiencyenhanced. The electrical and cooling circuitsare kept separate, further improvingreliability. Over the past 35 years Alstomstainless-steel cooling tube technology hasdemonstrated excellent reliability in operation.

• Direct hydrogen cooling of the rotor provides anearly uniform temperature all along the rotorbody, minimising the risk of thermal unbalance.

• Triple-circuit hydrogen sealing system for verylow hydrogen consumption with high and constanthydrogen purity and generator efficiency (a well-referenced technology on large fossil fired plants).

• Stator end-winding support structure design thatreduces maintenance effort and contributes to highavailability. It can be readily re-tightened duringa major overhaul, facilitating maintenance.

• Ease of inspection and maintenance, with innercomponents designed to be easily accessible.The rotor can, for example, be removed,without disassembling the end casing.

• Brushless excitation, further reducingmaintenance requirements and contributing tocompactness. And last but not least,

• Ease of transport.

The Flamanville 3 design includes 2 x 50%circulating water pump sets for main unitcooling, each providing 110 000 m3/h with 15.4m head. These pumps are of the concrete volutetype. They rotate at 151 rpm, and operate withan efficiency of 91.5%.

Concrete volute pumps have a number ofadvantages over conventional, full-metal,pumps, including long life, best resistance tocorrosion, reduced noise and vibration,together with minimum maintenance. Thecasing (volute) and suction duct are made ofstandard reinforced concrete, with a very robustdesign against corrosion and abrasion, whilegood maintainability is assured by employinga simple vertical shaft “pull-out” design thatallows critical parts such as the shaft and theimpeller to be easily removed for maintenance.

With low rotation speeds pressure losses arereduced and the mass of the concrete structureprovides the pumps with excellent inertiaproperties – all contributing to high efficiency,sustained over the whole machine lifetime.

The volute and suction line, both integratedinto the pumping station civil work, areparticularly resistant to corrosion and abrasion– and even in a seawater environment, as atFlamanville, fouling hazards are reduced.There is also minimal exposure of metal partsto water.

The Flamanville 3 pump sets include a fullyequipped pull-out section, complete electricalmotors and gear boxes. The contract scope alsoincludes a full set of formworks for thehydraulic concrete forms of both pumps.

Alstom has supplied more than 200 Bergeronconcrete volute pumps for condenser coolingpurposes worldwide.

The three 50% condensate extraction pumpsets for Flamanville 3 (two in operation, one instandby) are also being supplied by Alstom.These Bergeron pumps are of the vertical multi-stage bowl diffuser type, arranged inside asuction barrel. They are designed for highreliability (with experience at power plant sitesfor over 25 years with minimum servicing). Thedesign is based on double suction impellers,allowing reduced pump lengths but very high

efficiency. The barrel is installed in a concretepit below the condenser level and operatesunder condenser pressure.

The double suction is located at the verybottom of the pump in order to operate underthe best possible NPSH (net positive suctionhead) conditions. The suction impeller has beendesigned and tested to ensure the lowestrequired NPSH at all operating points, whilethe pressure stages are located as close aspossible to the pump discharge head.

The electric motor, which has its ownthrust-bearing device, is located on a separatecivil structure to avoid interactions with thepump itself, and to minimise vibrations.Alstom has already supplied more than 200such Bergeron condensate extraction pumpsfor nuclear power plant applicationsworldwide.

The engineering phase of the Flamanville 3turbine island is completed and manufacturingis almost finished.

The turbine island erection phase started inSeptember 2009 and equipment already on siteincludes main components for the condenser –which is the first major piece of equipment tobe installed – such as hot well, neck and tubebundles. Feedwater tanks, reheaters, HPheaters and LP heaters are also now on site.Turbine island construction is on target to hitits contractual schedule, which calls for themajor milestone of turning of the 70 m longshaft line – using the electrical turning gear –in 2011.

A key challenge in the manufacturing ofturbine island components has been to re-establish a complete supply chain, following along period in Europe without significantnuclear power plant orders. This had resulted ina diminished pool of players, lack ofcompetition, and high prices, making a globalapproach necessary, with the added challengeof ensuring that all components weremanufactured to the relevant Europeanstandards and required quality. Alstom’s widenetwork of dedicated sourcing professionalslocated in traditional supplier markets helpedthe Flamanville 3 project team to support a

global sourcing approach. All suppliers selectedadhere to Alstom’s high quality standardsincluding in terms of their technical capabilitiesand EHS aspects.

Timely manufacturing of the turbinecomponents for Flamanville 3 has involvedcollaboration among Alstom’s worldwidemanufacturing sites and its global network ofsuppliers. No less than 11 countries, includingthe USA and several in Asia, were involved. Aspart of this collaboration, a new millingmachine was sent from China to Alstom’sMorelia factory in Mexico, for manufacturingof the diaphragm with which theARABELLE™ steam turbine is equipped.

The steam turbine itself is being assembledin the Belfort factory in France. The Belfortworkshop has equipment that is among themost modern in Europe and its capacity for

making large, heavy rotors makes it one of theworld’s key manufacturing sites. The casingproduction line in the workshop wascompletely renewed in 2002 with three verylarge machining stations. In fact it has one ofthe world’s largest vertical machining centres,the VMG 10, which has an 8 m span betweencolumns and is able to machine the high andintermediate pressure casings for Flamanvilleand other EPR projects.

Globalisation brings its challenges,particularly when involving sub-contractors.Machining of the 8 m diameter LP inner casingfor Flamanville 3, for example, proved too timeconsuming for the sub-contractor initiallyselected. So to keep things on schedule, Alstomeventually had to take this work back into itsown facilities, Belfort for the inner casings andKarlovac for the associated exhaust structures.

This was more due to a scheduling issue than aquality issue. But there have also beeninstances where getting sub-suppliers to fullyunderstand the quality requirements took moreeffort than had been initially anticipated.However, the quality management is now inplace at these locations, and excellent work hasbeen done. This has included qualificationaudits to check the quality systems of thesuppliers including their technical capabilitiesand EHS aspects, as well as continuous checks,surveillance audits and inspections duringexecution.

The focus of turbine island activities has nowmoved from manufacturing to construction,where Alstom is on-site, working alongside itscustomer, EDF, to deliver the project to therequired high quality levels, within ademanding schedule. MPS