A U G U S T 2 0 1 9

TableofContents

1. Theissue....................................................................................................................2

2. Summary...................................................................................................................2

3. Utilizationofelectricitygenerationcapacity..............................................................3

4. Availabilityofelectricitygeneration..........................................................................4

5. Optionstoincreaseutilizationandavailability...........................................................8

5.1. Introduction...................................................................................................................8

5.2. Windpower...................................................................................................................8

5.3. Solarpower...................................................................................................................8

5.4. Hydroelectricpowerplants............................................................................................8

5.5. Nuclearpowerandotherthermalpowerplants.............................................................9

6. Nuclearpoweroutputduringheatwaves.................................................................10

7. Avoidingcurtailment...............................................................................................17

7.1. Introduction.................................................................................................................17

7.2. Upgradestoexistingplants..........................................................................................187.2.1. Optionsforexistingcoastalnuclearpowerplants.......................................................................187.2.2. Optionsforexistingriver-sitednuclearpowerplants..................................................................18

8. AbouttheAuthor.....................................................................................................20

8.1. StaffanQvist................................................................................................................20

1. Theissue

For the second summer in a row, some nuclear power plants in Europe have been forced totemporarilyshutdownorreducepoweroutputduetoextremeheatwaves.Somehavesuggestedthatthiscurtailmentdemonstratesthatnuclearenergyisill-adaptedtoawarmingclimate.Whydosomenuclearpowerplantshavetostopproducingelectricityduringheatwaves,andwhataretheimplicationsofthisissue?Aretherewaystofixthesituation?InthisarticleweexploretheimpactoftheEuropeanheatwavesof2003,2006,2018and2019onnuclearpoweroutput.

2. Summary

• Nuclearpowerplantsalreadyoperateatthehighestcapacityfactorandavailabilityfactorofany electricity generating technology. This is also trueduring heatwaves,whenwindandhydroelectricoutputcanbesubstantiallydepressed.

• Curtailmentofnuclearpowerduringheatwavesisnotaresultofsafetyconsiderations.Curtailmentprimarilyoccursatriversitedplantsandareduetolimitationsintheallowedtemperatureatwhichcoolingwatercanbereturnedtoariver.

• CurtailmentofnuclearpowerduetoperiodsofextremeheathashadtheeffectofreducingEuropeannuclearpoweroutputbyapprox.0.1%sincetheyear2000.ForFrancespecifically,whichwithitsmanyinlandriver-sitedplantshasbeentheworsthitcountry,thecorrespondingfigureisapproximately0.15%

• Atpeaktimes,lessthan5%ofEuropeannuclearpowercapacityhasbeenunavailablespecificallyduetocurtailmentduringrecentheatwaves.Evenattimesofpeakcurtailment,theavailabilityofnuclearpowerexceededthatofanyotherlow-carbonelectricitygeneratingtechnologyinEurope,includingsolarPV,windandhydroelectricity.

• Toaddressthisprobleminthenear-mid-term,technicalfixesarenotnecessarilyrequired.Forexample,theFrenchnuclearfleetrunsat60%capacityfactorduringthesummer,heatwaveornot,sinceitistypicallydeployedtovarywithload,andloadislowestinsummer,soscheduledoutagesarecommon.Electricitypriceshaveremainedmodestduringcurtailmentperiods(€40-60/MWh)andFrancecoversitsowndemandduringthesummer.Tocompensateforlostoutputatitsmostvulnerableriver-sitedplantsduringheat-wavecurtailments,Francecouldincreaseoutputattheremainderofitsfleetifeconomicincentiveswereprovided.

• Overthelongerterm,therearealsotechnicaloptionsreadilyavailableforalltypesofpowerplants,includingnuclear,toincreasebothratesofutilizationaswellasavailability.Thesewillalsobedrivenbyeconomics,notengineeringlimits.Thecostincreasesassociatedwiththeseoptionsarerelativelymodest.

3. Utilizationofelectricitygenerationcapacity

Commercialpowerplants(ofanytype)aregenerallyconstructed,maintainedandoperatedinawaywhichmaximizesprofitsfortheplant’sowners.1Thisrarely,ifever,2meansthattheplantsareconfiguredtoproduceelectricityattheirmaximumpossibleoutputforallhoursoftheyear.Ameasureoftheactualpowerproductionrelativetothemaximumpossiblepowerproductioniscalledthecapacityfactor(CF)andismeasuredinpercent.ACFof100%meansthepowerplantoperatesatmaximumcapacityallhoursoftheyear,whileaCFof20%meansitsannualoutputisonefifthofitstheoreticallyachievableoutput.TheannualcapacityfactorsfortheUnitedStatesin2018forallthemainelectricityproductiontechnologiesaregiveninFigure1.

Figure1,Annualutilizationofinstalledcapacity(capacityfactor),UnitedStates20183

AsisobviousfromFigure1,therearenorulesorregulationsforcingelectricitygeneratorstoalways produce at their maximum capacity. Instead, individual power plants makeinvestments that impact capacity factors and availability in a waywhichmaximises theirprofits.

1Theconstructionandoperationofallpowerplantsaresubjecttonationalandsometimesinternationalregulationandlaw.Additionally,electricgridoperatorsandenvironmentalagenciesmayimposeoperationalrestrictionstothewayplantsarebuildandoperate.2Smallerhydroelectricpowerstationslocatedinriversegmentswithveryabundantandsteadywatersupplymayintheoryapproachcloseto100%capacityfactorsduringprolongedperiodsbutwilleventuallyrequiregoingofflineformaintenance.Somemoderngeothermalplantshavealsobeenknowntohaveyearsatcloseto100%capacityfactor.3USEnergyInformationAdministration(2019)

4. Availabilityofelectricitygeneration

While there are no incentives or rationale for all generators to be configured to alwaysproduceattheirmaximumcapacity,thisisnotthesameassayingthatnoneofthemcoulddoso.Obviously,windandsolarplantsareatalltimeslimitedbytheresourcethatpowersthem,and therefore canneverbe calleduponatwill to increaseproductionwhenneeded.The“availability”ofsolarpower,definedastheoutputonecanreliablyexpecttoseeatanyonehouroftheyear, is0%.Thisisduetothecompleteunavailabilityofsolarpoweratnight.4While similarly one cannot guarantee any production from wind power, completely stillperiodsoverlargeareasoflandandseaarequiterare.Sincethereisusuallysomewindpoweravailableinageographicallydispersedandlargesystem,windpowerinaggregateistypicallyassignedareliabilityestimateof3-10%5.Thismeansthatsystemplanners“expect”that3-10%ofthepossibleproductionfromwindturbines(inaggregateacrossthesystem,notsinglegenerators)isavailableatanyonetime.Forpowerplantsthatusesomekindoffuelorstoredwaterastheenergyinput,thesituationisverydifferent.Aslongassufficientfueliskeptavailableonsite,thereareingeneral6notechnicallimitationsthatkeepsuchplantsfrombeingabletoproduceatmaximumcapacitywhencalledupon,atleastduringshorterperiods.Typically,powersourcessuchascoal,gas,oilandbiomass(bundledas“combustion”),conventionalhydroelectricandnuclearpowerareassignedanavailabilityfigureofupto~90%.Extremeheat-wavesreducestheavailabilityofalltypesofelectricityproduction,andalsohasnegativeimpactsontheavailabilityoftheelectricitygriditself.Hydroelectricpowerplantscansufferfromseveredroughtsandgeneralunavailabilityofwater.Allthermalpowerplants,includingnuclearpowerplants,operateatreducedthermalefficiencyasthewaterandairheatsup,andlocalregulationsmayforcecurtailmentsatsomeplants.Solarpanelsoperateatreducedefficiencyatveryhighairtemperatures.Windpoweroutputcandropdramaticallyduringheatwavesforextendedperiodsoftime,aswasseenmostrecentlythissummerinEurope.7A representativeavailability span (whichdependson local conditions) isgiven inFigure2.

4Solarpowerinaggregateinahypotheticalelectricitygridwithextremelongitudespread(acrossmanytimezones)mayintheorybeassignedahigherthanzeroavailabilityfigure.5Thisvaluecanbecalculatedandestimatedindifferentways,oneofwhichiscalculateanoutputdurationcurveandassignthereliableoutputfractionasonewhichis,forexample,reachedmorethan90%ofthehoursoftheyear.6Again,thisreportwillhighlighttheexceptionstothisgeneralization.7Overall,somemodelshavesuggestedthatwindavailabilityintheNorthernhemispheremaydecreasebyasmuchas15%duetofuturewarming.SeeKarnauskas,KristopherB.,JulieK.Lundquist,andLeiZhang."Southwardshiftoftheglobalwindenergyresourceunderhighcarbondioxideemissions."NatureGeoscience11.1(2018):38.

Figure2,Representativespanofavailabilityfordifferentpowersources

Europeanwindenergyoutput,showninFigure3,typicallydipsto its lowestvaluesduringsummer. Averaged over the entire summer of 2018, the total combined wind energyavailabilityacrossallEUmemberstateswasabout14%.

Figure3,WindEnergyoutputandinstalledcapacityinEurope(EUmemberstates)in20188

Averaged over shorter time durations and smaller geographical areas, the minimumavailabilityofintermittentenergysourcessuchaswindandsolarPVdropsfurther.Historicproductionstatistics shown inFigure4 indicate that theminimumcombinedoutputofallwindandsolarpowerinEuropecandropbelow2%duringsinglehours,andbelow5%forperiodsaslongas48hours.Minimumcombinedshorter-termoutputperiodstypicallyoccur

8DatafromWindEurope,“WindenergyinEuropein2018Trendsandstatistics”(2019).Installedcapacityisassumedtobelinearlyincreasingfromstarttoendofyearvalues,actualtrendmaydiffer.

in the summer nights and longer-term minimum output typically occurs in early fall(SeptemberandOctober).

Figure4,MinimumcombinedcapacityfactorofSolarandWindenergyinEurope(basedhourlydata2012-2016fromnationalTSOsandENTSO-E)

Theavailabilityofnuclearandhydroelectricpowerplantsisalsoseasonallydependent,risingtopeakvalues(~90%)duringtimesofpeakelectricitydemand.Sinceavailabilityistypicallylessimportantduringseasonsoflowdemand,theiravailabilityinaggregateis,byplanning,lower.NuclearplantsinEuropescheduletheirannualoutageformaintenanceandrefuellingduringlatespring,summerandearlyfall,whenelectricitydemandisthelowest.Similarly,hydroelectric plantswith large reservoirs operate at low capacity during these periods inorder to savewater for higher demand periods in thewinter. Scheduled outages can beshiftedintimetoincreasebothproductionandavailabilitytospecificallytackleheatwaves,ifthisisdeemednecessary.Forexample,theFrenchnuclearfleetrunsat~60%capacityfactorduringthesummer,heatwaveornot,sinceitistypicallydeployedtovarywithload,andloadislowestinsummer,soscheduledoutagesforrefuelingarecommon.Frenchelectricitypriceshaveremainedmodestduring curtailment periods (€40-60/MWh) and France covers its own demand during thesummer. Therefore, to compensate for lost output in its river-sited plants, France couldincreaseoutputattheremainderofitsfleetoralteritsscheduledoutageplanningifsufficienteconomicincentiveswereprovided.Anapproximatecomparisonbetweenthesummertimenuclear availability, planned unavailability and the impact of heat-wave curtailmentcomparedtoFrenchsummertimeelectricitydemandisgiveninFigure5.

Figure5,Comparisonbetweenelectricitydemand,availablenuclearcapacity,plannedunavailablenuclearcapacityandheatwavecurtailmentinFranceinsummertime

5. Optionstoincreaseutilizationandavailability

5.1. Introduction

Therearetechnicaloptionsreadilyavailableforall typesofpowerplantsto increasebothratesofutilization(raisingthecapacityfactor)aswellasavailability.However,absentspecificregulations,iftheplantdoesnotincreaseprofitsbyinvestmentsthatraisethecapacityfactororavailabilityfactor,suchinvestmentswillnotbemade.5.2. Windpower

Windpowercapacityfactorsarephysically limitedbythelocalavailabilityofwind.Awindturbinewith a very highhubheight, very longblades and a small generator capacitywillproduceatafarhighercapacityfactorthanonewithashorterhubheight, largercapacitygeneratorandshorterblades.Somewindturbinemanufacturershavetakenmodeststepsinthisdirection,producingwhatisreferredtoas“lowspecificpowerdesigns.”Intheory,onecoulddesignawindturbinethatproduceselectricitynearratedpowerevenatverylowwindspeeds,butsuchdesignswouldincreasecosts.5.3. Solarpower

Solarpowerplantcapacity factorsarephysically limitedby insolation,but thiscanstillbeadjustedbysystemdesign.Solarpanelsproducedirectcurrent(DC),whichistheninvertedintoalternatingcurrent(AC)tobefedtotheelectricgrid.Typically,theinstalledDCcapacityofthesolarpanelsishigherthantheinverterACcapacitybyafactorof1.1-1.3(thisiscalledthe“loadratio”).Systemsaredesignedthiswaybecauseitisnoteconomicallyjustifiabletoinvest inan inverterandgridconnectiontohandletheabsolutepeakDC load,whichmayoccurjustbrieflyinthemiddleoftheday.Averyhighloadratiohastheeffectofraisingthesolarcapacityfactor(whichisbasedoninverterACcapacity)whilereducingtotalelectricityfedtothegrid.Generalavailabilityisnotincreasedunlessstorageisadded,sincethereisstillnoproductionatnight.5.4. Hydroelectricpowerplants

Theoutputofahydroelectricpowerplantislimitedtotheannualin-flowoftheriversystemtowhichtheplantisconnected.Forarun-of-riverplant(wheredamsdonotregulateflowtoanyimportantdegree),raisingthecapacityfactorandavailabilityistechnicallyverysimple.Run-of-river plants with turbines and generators sized to match the expected annualminimumflowrateof the river sectionwhere theplant is sitedwouldachieveaveryhighcapacity factorandavailability.This typeofcapacityderatingwouldhoweverdramaticallyreduceelectricitygenerationandtheeconomicviabilityofsuchplants.

5.5. Nuclearpowerandotherthermalpowerplants

Nuclearpowerplantstypicallyrankatornearthetopofallavailableoptionsforbothcapacityfactor and availability inmost places where they are present, but there is still room forimprovement.Atcertainriver-sitedpowerstations,poweroutputoccasionallyneedstobereduced,andsomeplantsneedtoshutdownentirelyduringextremeheatevents.Sincetheseeventsoccurveryinfrequentlyandtypicallyonlylastsforafewdays,ithasnotbeendeemedcost-effectivetomaketheinvestmentsrequiredtobeabletocarryonproducingatmaximumcapacityduringsuchevents.Thelostincomefromreducedelectricitysalesduringafewdaysin thesummerevery fewyearsmaybe less thantheexpenses incurred from investmentsrequiredtoavoidforegoingthisproduction.Inthissense,thesituationisexactlythesameasthelackingeconomicmotivationtofurtherincreaseavailabilityandutilizationofwind,solarandrun-of-riverhydroelectricpower.

6. Nuclearpoweroutputduringheatwaves

For nuclear and other thermal power plants (coal, combined-cycle gas, oil, biomass etc.)situatedatinlandriverlocations,theavailabilityandtemperatureofcoolingwatermaygiverisetoproblemsduringextremeheatwaves. Insuchcases,thepowerplantsmayhavetoreducetheirpoweroutputortemporarilystopproduction.Curtailmentofnuclearpowerduringheatwavesisnotaresultofsafetylimitations.Thisisinstead usually in response to environmental regulations which limit the temperature atwhich the plant is allowed to return coolingwater to a river. 9 Coastal power plants aregenerallyunaffectedbyextremeheatwaveeventsduetothemorelimitedimpacttemporaryheatwaveshaveonthetemperaturesoflargerbodiesofwatersuchasalargelakeorocean.Since2000,therehavebeenfourmajorheat-waveeventswherenuclearpowerplantoutputhasbeensignificantlycurtailed:inthesummersof2003,2006,2018and201910.France,thelargest nuclear power producer in Europe and second globally (behind theUS), has beenhardesthit.ThisismainlybecausetheFrenchnuclearfleethasalargenumberofplantssitedat inland river locations. The heat wave of August 2003 was exceptional in its duration,intensityandextensionandcausedtemporarycurtailedoutputat30nuclearreactorsacrossEurope.Theheatwavesof2006,2018and2019mainlyimpactedFrenchplants.Apartfromplants in France, heat-wave curtailment of significance after 2003 is known to also haveoccurredattheRinghals-2reactorinSweden11,theLoviisaplantinFinland,theMühleberg&BeznauplantsinSwitzerland,theSantaMariadeGaronaplantinSpainandtheIsar,Brokdorf& Grohnde plants in Germany. French nuclear output has in total been reduced byapproximately12TWhduetoextremeheat-wavecurtailmentsince2000,whichcorrespondstoabout0.14%oftotalnuclearoutputduringthesameperiod.Actualoutputandheat-wavecurtailmentisshowninFigure6.

9However,ifthereexistsanurgentneedforelectricityproduction,regulatorybodiesaresometimeswillingtograntatemporaryexemptionfromthecoolingwatertemperaturerestrictions.DuringtheheatwaveinAugustof2003,threereactorsattheTricastinplantandoneattheGolfechplantinFranceoperatedfortendaysundercoverofthesetemporaryprovisionstoavoidsupplydisruptions.10Someveryminorcurtailmentisknowntohaveoccurredinotheryears,forexamplein2015.11Of the curtailment events that havebeendescribed, forced reductions in coastal power plant output areexceptionallyrare,butexamplesdoexist.InlateJuly2018,thepowerofthecoastal-sitedRinghals-2reactorinSwedenwastemporarilycurtailedto49%duetoseatemperaturesgoingabove25°C.ThisistheonlyknownoccurrenceofaSwedishreactorreducingpoweroutputduetoseawatertemperature.Duetothiscurtailment,around85GWhofpossibleproductionwaslost,whichcorrespondsto0.1%ofSwedishnuclearpoweroutputthatyear.

Table1,EstimatednuclearpowerplantcurtailmentduetoheatwavesinEurope

Heat-waveCurtailednuclearoutputduetoheat-waves(TWh)

France RestofEurope12 Total

2003 5.513 2-3 7.5-8.5

2006 2.5 0.5-1.0 3-3.5

2018 1.714 0.3-0.6 2-2.6

2019 1-2 0.2-0.5 1.2-2.5

Otheryears 0.3 0.2 0.5

Sum 11-12 3.2-5.3 14.2-17.3

Figure6,Actualnuclearpowerplantoutputandapproximatelostoutputduetoheat-wavecurtailmentinFrance(2000-2019)[preliminaryfiguresfor2019]15

OutsideofFrance,themajorityofnuclearpowerplantsarelocatedonlesssensitiverivers,large lakesorat thecoast, so the relative impactofheat-wavecurtailment is significantlysmaller. An estimation of the impact of extreme heat-wave curtailment on total nuclearpowerplantoutput inEurope isgiven inFigure7.The total lostoutputduring theperiodshownisapproximately0.1%.

12Thisisaroughestimatebasedonnewsreportsaboutcurtailments13SFEN“Adapterlescentralesnucléairesauchangementclimatique”(2015)141.7TWhisaccordingtothisreport:https://www.montelnews.com/en/story/intense-heatwaves-no-longer-a-threat-to-nuclear-fleet--edf/1021785,actualcalculatedlostoutputfromFrenchunavailabilitydatais0.1TWh.Thereasonforthedifferenceisnotclear.15BPStatisticalReviewofWorldEnergy2019,SFEN“Adapterlescentralesnucléairesauchangementclimatique”(2015)andNucleonicsWeek60(2019).Nuclearoutputnumbersconvertedtonetfiguresbysubtracting4.1%self-consumptionofelectricity.2019outputfiguresareestimatedfromproductiondatauntilJune2019andcomparedwithpreviousyearsofoutput.

Figure7,Actualnuclearpowerplantoutputandapproximatelostoutputduetoheat-wavecurtailmentinEurope(2000-2019)[preliminaryfiguresfor2019]16

While lost generation is marginal compared to annual output, the larger worry is theavailabilityofthepowerduringthehoursanddayswherereliableelectricityiscritical.Theunavailability of nuclear power in Europedue to heatwave curtailment hasmomentarilyexceeded 5 GW, or about 4% of the Europe’s installed nuclear power. However, Frenchnuclearenergyoutputandavailabilityduringyearsofheatwavesandcurtailmentdonotdiffernoticeablyfromyearswithoutsevereheatevents,ascanbeseeninFigure8.Summer-month output of nuclear energy was in fact 2.1-2.7% higher in 2018 (when heat-wavecurtailmentoccurred)comparedtotheprecedingtwoyears.

16BPStatisticalReviewofWorldEnergy2019,SFEN“Adapterlescentralesnucléairesauchangementclimatique”(2015)andNucleonicsWeek60(2019).Nuclearoutputnumbersconvertedtonetfiguresbysubtracting4.1%self-consumptionofelectricity.2019outputfiguresareestimatedfromproductiondatauntilJune2019andcomparedwithpreviousyearsofoutput.

Figure8,WeeklycapacityfactorofFrenchnuclearenergyfor2016,2017and2018

Figure9givesthepoweroutputin30-minuteincrementsoftheFrenchnuclearfleetduringthesummerof2018comparedtothespanofvaluesfromthefiveprecedingsummersduringwhich there were no extreme heat events and no curtailment. The output is within theboundsofthetypicaloutputduringsummer,andagainnodiscernibleimpactisseenduringthecurtailmentperiod.

Figure9,ComparisonofFrenchnuclearoutputduringanextremeheatwave-strickenyear(2018)and

fiveyearswithoutextremeheatwaves(2013-2017)

The capacity factor duration curve of low-carbon electricity sources in France during theextremeheat-wavesummerof2018isshowninFigure10.Althoughnuclearwasstruckbyheat-wavecurtailmentthatsummer,itstillshowsasteadierandmorereliablepoweroutput(i.e.“flatter”)durationcurvethantheotheravailablelowcarbonelectricityoptions.Anotherwaytoshowthisisbyscalingupsolarandwindoutputacrossthissummertothelevelofactualnuclearoutput.Figure11showsFrenchsolarPVscaleduptoprovidethe~86TWhsofelectricitythatnuclearprovidedinthesummerof2018.Poweroutputinthisexamplevariesbetweenzeroand135GW,toprovidetheaverageoutputof~39GW.WindpowerhasbeenscaledinthesamewayinFigure12,andshowsanoutputvariationbetween1.4GWand158GW. Figure 12 shows that depressed output of wind can last over week-long periods. Ahypotheticalblendof50%windand50%solarscaledtonuclearoutputacrossthesummerisseeninFigure13.Thecombinedwindandsolaroutputvarybetween3GWand117GWandcanremainlowovermultipleweekperiods.Thus,whileheat-wavecurtailmentofnuclearpowerplantsdoesreduceitsavailabilityandreliabilityasapowersource,thisimpactisrelativelysmallwhencomparedtotheinherentvariabilityofoutputinotherlow-carbonelectricityoptions.

Figure10,Durationcurveforcapacityfactoroflow-carbonelectricityinFranceduringthesummerof

2018(June1sttoAugust31st)

Figure11,FrenchSolarPVoutputscaleduptonuclearoutputacrossthesummerof2018

Figure12,Frenchwindpoweroutputscaleduptonuclearoutputacrossthesummerof2018

Figure13,Frenchwindandsolarpoweroutputscaleduptocombinedmatchnuclearoutput

acrossthesummerof2018

7. Avoidingcurtailment

7.1. Introduction

It is obvious from the data presented in previous sections that heat-wave curtailment iscurrentlyamarginal issuewithavery loweconomic impactonnuclearpowerproduction.However, changes in the global climatemake extremeweather eventsmore likely goingforward. It is telling that out of the 4 recent periods inwhich significant curtailment hasoccurredinEuropesince2000,twooccurredinthelasttwoyears.Withincreasinglikelihoodofcurtailmentinthefuture,theeconomiccaseforinvestmentstoovercometheseproblemsbecomes more appealing. At present levels, which indicates a medium-term loss ofproduction of ~0.1-0.15%/year, only relatively minor (and cheap) modifications can bejustified to mitigate the situation. However, regulatory requirements as well as publicrelationspressuremayinducenuclearpowerplantoperatorstononethelessmakesignificantinvestmentstoovercometheseissueseveninthenearterm.Inresponsetothecurtailmentsof2003and2006,ElectricitédeFrance(EDF)launchedthe"Grands Chauds" (“Great Heat”) project. This project examines the prospects for climatechange,analyses the impactontheFrenchnuclearpower fleetanddefines thenecessaryadaptationsbothforsafetyandavailability.Referenceplantdesigntemperatureshavebeenadapted,sitebysite,forbothairandwater.Forexample,atthepeakofthemostextremeheateventtodate(thatofAugust2003),temperaturesoftheLoireriverthatcoolstheChinonnuclearpowerplantwereashighas32.5°C.AttheTricastinplant,thehighesteverrecordedairtemperature(alsoin2003)was42.5°C.GoingforwardtheChinonplantwillbeadaptedtomanageawatertemperatureof37°CintheLoireriver,whiletheTricastinplantshouldhandleairtemperaturesof46°C.Ingeneral,theplantsinvolvedintheGrandChaudsprogramhavehad their design temperatures updated to be 3-5°C above the peak temperatures everrecordedintheairandwateratthesesites.Giventhatextremeweathereventsarelikelytobecomeevermoreextremeandfrequent,itisnotguaranteedthatsuchmodificationswillpreclude any curtailment in the future. However,with the program in place, the relativefrequencyandimportanceofcurtailmentarelikelytofall.

7.2. Upgradestoexistingplants

7.2.1. Optionsforexistingcoastalnuclearpowerplants

Thedocumentationandanalysisfortheoperationofthecomponentsandsystemsofnuclearpowerplantsaredefinedforsomespecificmaximumtemperatureoftheairandseaorriverwater. For many plants, the original analysis and determination of these “referencetemperature”valuesweredonein1970sand80sandmaythereforenotbeapplicableforthepeaktemperatureconditionsofthe2000sandbeyond.While the Swedish coastal-sited Ringhals-2 was temporarily forced to reduce power, nocurtailmentwasneededattheadjacentRinghals1,3and4reactorsatthesamesite.TheonlydifferenceofnoteisthatatRinghals-2,thedocumentationforoneofthecoolingcircuitsonlyextendedtocasesofwatertemperaturesupto25°C.Relativelyminorwork,whichmayinfactbe limited to simply reanalysingand resubmittingdocumentation forone subsystem,wouldbeneededtoraisethefull-powermaximumseawatertemperatureto27°C, in linewiththerestoftheRinghalsreactors.Oneengineeringoptiontofuture-proofanycoastalplantwhilealsoincreasingpoweroutputis to installadeepwater intake forcoolingwater.Rather thantakingwater fromnear thesurface,coolingpipesareextendeddowntodeeperandcoolerwaters,wheretemperaturesareconsistentlycoldevenduringheatwaves.Suchanadaptationwouldcostapproximately$100millionfora1GWeplantandisthereforerarelyeconomicallyjustifiedcomparedtothelostoutputitwouldcompensatefor.7.2.2. Optionsforexistingriver-sitednuclearpowerplants

Thereisawidearrayofpotentialupgradeoptionstoallowforriver-sitednuclearpowerplantstobeoperatedatfullpowerevenduringextremeheatwaveevents.

1. Somenuclearplantslocatedonlargeriverswithhighflowratesuseopenloop(once-through)cooling.Thesearethetypesofplantsthatmostcommonlyfacecurtailmentduring heat waves. Adding recirculating wet cooling towers at these sites wouldreduce water withdrawal from the river by at least 95% and, given enough areaavailable for towers, could be dimensioned in a way as to preclude any futurecurtailment. The total cost for cooling tower capacity for a 1GWeoutput plant isapproximately$100million.17

2. Someplantsuseacombinationofopenloopandcoolingtowercooling,suchastheoccasionally curtailedBugeynuclearplanton theRhone river.A transition to fully

17KoenRademaekersetal.,“InvestmentneedsforfutureadaptationmeasuresinEUnuclearpowerplantsandotherelectricitygenerationtechnologiesduetoeffectsofclimatechange,”EuropeanCommission,Brussels,Belgium,2011.

closed-loopcoolingusing2additionalrecirculatingwetcoolingtowerswouldreducewater withdrawal requirements sufficiently to preclude curtailment altogether. Ifsufficient land area is available, an artificial pond could be added, as has beenimplementedattheCattenomplant,whichwouldfurtherreducetherelianceonriverwater.

3. Forhypotheticalplantslocatedatsiteswherenowater-coolingofanykindisavailable,forinstancebyacompletelydriedupriver,dry-coolingoptionsareavailable.Nosuchsitestoberetrofittedexists,but itmaybeanoptionforfuturesitingofplants, forexampleinfarin-landChina.

TheapproximatewaterusageofthedifferentoptionsisgiveninTable2.

Table2,Nuclearplantwaterusewithdifferentcoolingoptions

# Solution

Waterwithdrawnfromriver(m3/MWh)

Waterevaporated(m3/MWh)

Waterreturnedtoriver(m3/MWh)

1 Directcooling(openloop) 75-230(1) ~1.5(2) (1)-(2)2 Recirculatingwetcoolingtower

(naturaldraft)3.0-4.2 ~2.8 0.2-0.8

3 Recirculatingcoolingpond 1.9-4.2 1.7-3.4 0.2-0.84 Drycooling 0 0 0

8. AbouttheAuthor

8.1. StaffanQvist

EnergyEngineerPh.D.,NuclearEngineering,UCBerkeley,2013M.S.,MechanicalEngineering,RoyalInstituteofTechnology(KTH),2010B.S.,MechanicalEngineering,RoyalInstituteofTechnology(KTH),2008STAFFANA.QVISTisaSwedishengineerandconsultanttocleanenergyprojectsaroundtheworld.HeleadstheconsultancyQvistConsultingLimitedandlivesinLondon.Staffanistheco-author,withJoshuaS.Goldstein,ofABrightFuture:HowSomeCountriesHaveSolvedClimateChangeandtheRestCanFollow(PublicAffairsBooks,January2019).NewYorkTimesBookReview(2019):https://www.nytimes.com/2019/02/05/books/review/bright-future-joshua-s-goldstein-staffan-a-qvist.htmlFinancialTimesReview(2019)https://www.ft.com/content/ec785c86-1021-11e9-acdc-4d9976f1533b“ABrightFuturestartswithabang.“Fewbookscancrediblyclaimtoofferawaytosavetheworld,butthisonedoes,”thepsychologistStevenPinkerwritesinhisforeword.Thatisaboldassertion,butbythetimeIhadfinishedthebook,Iwashalf-convincedhewasright.”