Module 08Module 08MagnoxMagnox and and

AdvancedAdvanced Gas Gas CooledCooled ReactorsReactors(AGR)(AGR)

Prof.DrProf.Dr. . H. H. BBööckckVienna University of Technology /AustriaVienna University of Technology /AustriaAtominstituteAtominstituteStadionalleeStadionallee 2, 2, 1020 Vienna, Austria1020 Vienna, Austriaboeck@ati.ac.atboeck@ati.ac.at

Nuclear Power Nuclear Power PlantsPlants in in thethe UKUK

All Reactors: Coolant ChoicesAll Reactors: Coolant Choices

Plant Operation licences ends BNFL plans closure Age at closure

Calder Hall 2006/ 2008 Shut down 03/2003 50

Chapelcross1,2,3,4 2008/ 2010 Shut down 06/2004 50

Bradwell 2002 Shut down 02/2002 40

Dungeness A1,A2 2006 Shut down 12/2006 40

Sizewell A1,A2 2006 Shut down 12/2006 40

Oldbury 1,2 2008 2008 40

Wylfa 1,2 2004/ 2004 2009* 38

Status of Status of MagnoxMagnox ReactorsReactorsbyby 20062006

TypicalTypical MagnoxMagnox LayLay--outout

Magnox Cross SectionMagnox Cross Section

Cross Section through Cross Section through MagnoxMagnox CoreCore

MagnoxMagnox: : OldburyOldbury AA

OldburyOldbury TechnicalTechnical DataData

Electric Output Electric Output grossgross 450 450 MWMWee CoreCore heightheight 9.8 m9.8 m

Electric Electric outputoutput netnet 435 435 MWMWthth CoreCore diameterdiameter 14.2 m14.2 m

Thermal Thermal efficiencyefficiency 28%28% NumberNumber of of fuelfuel channelschannels 33083308

Thermal powerThermal power 815 815 MWMWthth NumberNumber of of controlcontrol rodsrods 101101

COCO22 inletinlet temptemp.. 220 220 ººCC FuelFuel rodsrods per per channelchannel 88

COCO2 2 outletoutlet temptemp.. 365 365 ººCC LengthLength of of fuelfuel rodrod 97.3 cm97.3 cm

MassMass of of UUnatnat 292 t292 t Diameter of rodDiameter of rod 28 mm28 mm

PressurePressure vesselvessel heightheight 31.7 m31.7 m FuelFuel UUnatnat

PressurePressure vesselvesseldiameterdiameter

32.6 m32.6 m CladdingCladding MagnoxMagnox alloyalloy

MagnoxMagnox FuelFuel ElementElement

•Natural metallic uranium as fuel •Magnox alloy: 99%Mg, rest 0.8% Al0.002-0.05% Be, 0.008% Ca, 0.006% Fe

•Fuel: 1 m long, 10 cm diameter

Refuelling MachineRefuelling Machine

• 6-10 elements per channel connected by a steel rod

• 100 mm diameter • All fuel elements in

one channel replaced together

• 2000-6000 channels depending on reactor type

• On-load refuelling

MAGNOX Reactor Limits MAGNOX Reactor Limits

• Max Tfuel <560 ºC (Phase change at 660 ºC with 10% volume increase)

• Max Tclad <450 ºC (high creep rate above 560 ºC)

• Channel size is a trade-off between leakage, heat transfer and pressure drop

• At a temperature of about 680 ºC increasing disintegration of CO2+C to 2 CO, prevention by CO2doping with methane

MAGNOX MAGNOX Reactor Reactor LimitsLimits

• Tout ~ 400 ºC: reduced steam temperature and reduced efficiency to ~ 30%

• Steel absorbing rods to flatten radial power• Power density ~ 1kW/litre (PWR 80kW/litre, BWR

50kW/litre)

MAGNOX Reactor ControlMAGNOX Reactor Control

• Safety Rods (1-2% reactivity)• Coarse rods• Fine rods (Steel rods)• Secondary shut down system by boron-

steel balls and boron dust powder• Only 0.5 % of U utilisation• Produces ~ 550 kg Pu / 1000 MWe

(PWR produces 280 kg Pu/ 1000 MWe)

Advanced GasAdvanced Gas--Cooled ReactorCooled Reactor

• Large graphite moderator

• High initial cost • Low power density

~ 6 kW/litre• 8 fuel elements coupled

together on a SST rod and refuelled together on load

AGR Cross SectionAGR Cross Section

Internal gas ducts

Standpipes through PV

AGR Fuel & CoreAGR Fuel & Core• Higher temperatures to produce better steam quality• UO2 ceramic fuel• Enriched fuel required (approx. 2%)• Stainless steel cladding

– oxidation in CO2 at 800 ºC– Low conductivity– High σabs

• Higher power density requires cluster type fuel to optimise surface to volume ratio

• TFuel <1300 ºC• TIn ~310 ºC• TOut ~675 ºC• Tsteam ~553 - 650 ºC• TGraphite ~500 ºC to reduce C loss• Surface structured rods to increase turbulence and heat transfer• Lower Pu production than Magnox

AGR Fuel AssemblyAGR Fuel Assembly

• 36 fuel pins per assembly • Graphite sleeve• Separates coolant from

bulk moderator

AGR Fuel ChannelsAGR Fuel Channels

• 7-8 elements coupled together on stainless steel bar

• 1 refuelling stand-pipe per channel

• Monthly refuelling

Gas Flow in AGRGas Flow in AGR

• Separate coolant flow streams: Hot through core • Cold: Up in the gap between steel liner and core

to cool the pressure vessel (liner)• Down through graphite channels in the

moderator blocks at 350 ºC• Up the fuel channels (hot)• Out from the side of the standpipes in the gas

dome above the core • Down to gas circulators through boilers

AGR: AGR: HinklkeyHinklkey Point BPoint B

AGR SafetyAGR Safety

• Prestressed concrete pressure vessel – Redundant layers – steel liner, no external gas ducts– Rapid depressurisation low probability

• Control rod standpipes– Flexible rods– Pressure vessel

• Diverse Secondary Shutdown Systems– Nitrogen gas purge– Boron dust (=death to reactor)

ReferencesReferences

•• http://www.karehttp://www.kare--uk.org/magnoxes.htm#9uk.org/magnoxes.htm#9•• http://www.bnfl.com/index.aspx?page=41http://www.bnfl.com/index.aspx?page=41