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- 2. 1.0 Introduction? The?object?of?the?6?week?internship?was?to?learn?more?about?the?thermal?hydraulic?and? safety?aspects?of?PWRs,?more?specifically?the?AP1000.?This?work?was?conducted?under?the? supervision?of?Ms.?Zhen?Xu?from?Shanghai?Nuclear?Engineering?Research?and?Design?Institute? and?Professor?Wang?from?the?University?of?Michigan.?? The?following?is?the?typed?schedule?for?the?internship,?assigned?and?proposed?by?Ms.Zhen?Xu:?? Date? Job?content? July.1?st? ?CJuly.10?th ?? Read?and?understand?the?section?1.1、1.2、4.4、and?chapter?15?of?DCD?of? AP1000.? July.10?st? ?CJuly.19?th ?? Read?and?understand?the?section?7?in?chapter?4?of?volume?III??and?section?5?in? Chapter?5?of?volume?II?in?document?of?URD,?summarize?the?requirements? relate?to?core?design?and?accident?analysis.? July.20?st? ?CJuly.24?th ?? Gather?the?latest?international?laws?and?regulations?related?with?the?thermal? hydraulic?analysis?of?PWR.?Then,?search?for?the?document?about?the?EPR,?and? finish?a?report?comparing?the?characteristic?of?ESF?of?EPR?and?AP1000.? July.25?st? ?Aug.6?th ?? Calculate?the?cases?of?＾Malfunction?of?feedwater?system?which?cause?the? decrease?of?feedwater?temperature￣?and?＾RCS?boron?concentration?balance? design?transient￣.? Aug.7?th? ?Aug.12?th ?? Accomplish?a?report?which?summarizes?the?work?and?results?during?the? internship?of?this?two?months.? ? This?report?is?an?all?encompassing?report?that?combines?the?previous?reports?and?the? recent?calculations?that?were?finished?on?the?12?th? ?of?August.?Upon?completion,?this?report?will?be? turned?as?my?semester?assignment?for?NERS?499?under?Professor?Wang.?? ? ? 2
- 3. 2.0 AP1000? 2.1 Vol.?3?Sec.7?Chpt.?4?C?Reactor?Systems? 2.1.1 PWR?Core? The?basic?core?design?for?a?PWR?must?fulfill?proper?design?expectations?while?trying?to?be? economically?feasible,?as?well?as?being?within?engineering?safety?limits.?A?core?design?consists? of?fuel?assemblies,?fuel?rods,?control?rods,?reactivity?control?system,?neutron?system?and?core? instrumentation.?? ? The?major?functions?that?the?PWR?core?accomplish?are:? ¢ Fuel?systems?that?provides?adequate?power?and?cycle?energy?production.?? ¢ Fission?products?and?fuel?are?contained?within?cladding.? ¢ The?control?of?excess?reactivity?in?the?core.? ? Control?rods?for?short?term?reactivity?adjustment.? ? Dissolved?poison?concentration?in?coolant?for?long?term?reactivity?adjustment.? ? e.i.?Fuel?depletion?and?Reactor?cool?down? Assembly?layout?and?loading?pattern?are?determined?by?obtaining?a?realistic?minimum?level?of? neutron?leakage?at?the?perimeter?of?the?assembly,?and?for?a?negative?moderator?temperature? coefficient?at?critical?level?operation.?Control?rods?should?be?easily?inserted,?and?capable?of? properly?initiating?scram.?Lastly,?the?core?should?be?designed?to?not?undergo?bulk?boiling?in?the? hot?channel?under?standard?operating?conditions.?Overall,?the?material?used?in?fuel?assembly? construction?should?be?corrosive?resistant?to?prevent?fretting?damage?and?damage?to?the?stainless? steel?springs.?Therefore,?the?material?used?must?be?mechanically?sound?to?hold?the?weight?of?the? assembly?and?not?corrode?in?the?core?environment.? ? 2.1.2. PWR?Material? The?fuel?system?in?a?PWR?core?should?maintain?a?high?neutron?economy,?but?should?be? mechanically?sound?and?corrosive?resistant.?A?common?cladding?material?is?Zircaloy?due?to?its? high?corrosive?resistance.?Unfortunately,?it?has?a?higher?tendency?of?hydrogen?formation?causing? a?plethora?of?other?problems.?Ultimately,?standard?designs?limit?hydrogen?formation?to?less?than? 2ppm?on?a?Uranium?weight?basis.?For?control?rods,?the?material?composition?changes?depending? on?the?exposure.?For?example,?in?the?AP1000?design,?Wet?Annular?Burnable?Absorbers? (Ag?In?Cd)?and?Integrate?Fuel?Burnable?Absorbers?( )?are?used?for?high?and?low?exposureCB4 ? settings?respectively.?IFBAs?coat?the?surface?of?the?fuel?rods,?while?the?WABAs?take?up?open? spaces?in?the?guide?tubes.? 3
- 4. 2.2. Vol?2.?Sec.?5.?Chpt.?5?C?PWR?Core?Damage?Prevention?Requirements? 2.2.2. General?Requirements? Analysis?of?core?coolant?inventory?control,?and?decay?heat?removal?system?using?the?following? core?safety?features:?? ¢ Residual?Heat?Removal?? ¢ Emergency?Feedwater? ¢ Safety?Injection?System? ¢ Safety?Depressurization?and?Vent?System? Further?analysis?of?the?safety?system?will?include?the?use?of?motor?driven?and?turbine?driven? pumps,?as?well?as?the?heat?exchanger?used?in?the?RHR?and?valve?systems.?All?these?system? should?be?readily?available?for?control?and?monitoring?during?start?up,?steady?state?and?cool? down?operations.?? 2.2.3. Residual?Heat?Removal?System?(RHR)? To?begin,?the?RHR?system?does?a?variety?of?different?functions?from??decay?heat?removal? along?with?RCS?heat?removal?to?transferring?water?from?refueling?cavity,?removing?heat?from?the? IRWST?during?feed?and?bleed,?lower?the?temperature?during?overpressure?conditions?and?as?a? potential?back?up?to?the?CSS?during?a?long?term?LOCA.? The?RHR?system?in?a?PWR?takes?water?from?one?or?two?RCS?hot?legs,?cools?it,?and? pumps?it?back?to?the?cold?legs?or?core?flooding?tank?nozzles.?The?suction?and?discharge?lines?for? the?RHR?pumps?have?valving?to?provide?reasonable?assurance?that?the?low?pressure?RHR?system? is?isolated?from?the?RCS?when?the?RCS?pressure?is?greater?than?the?RHR?system?design?pressure.? Relief?valves?are?provided?to?protect?the?RHR?system?from?an?overpressure?condition,?although? the?relief?capability?is?not?sufficient?to?protect?the?RHR?system?from?an?overpressure?condition?if? isolation?valves?are?open?when?the?RCS?pressure?is?significantly?greater?than?the?RHR?design? pressure.?? In?PWRs,?the?RHR?system?is?also?used?to?fill,?drain,?and?remove?heat?from?the?refueling? water?cavity?during?refueling?operations,?to?circulate?coolant?through?the?core?during?plant? startup?before?RCS?pump?operation,?and?in?some?to?provide?an?auxiliary?pressurizer?spray.?? Like?many?safety?features,?redundancy?is?implemented?to?prevent?complete?failure?of? RHR?function.?Therefore,?the?RHR?has?two?independent?systems?as?a?precaution.?Furthermore,? in?the?case?of?low?RCS?water?levels,?the?RCS?is?actually?designed?to?never?go?below?the? minimum?water?level?for?RHR?operation.?? 4
- 5. 2.2.4. Emergency?Feedwater?System?(EFW)? In?the?case?of?loss?of?feedwater,?the?EFW?will?be?triggered?and?will?begin?inserting? feedwater?at?a?systematic?flow?rate?into?the?Steam?Generator.?The?flow?rate?will?depend?on?the? following:? ¢ Potential?spills?in?Steam?Generator? ¢ Status?of?Reactor?Coolant?Pumps? ¢ Single?Failure? There?is?a?risk?of?overcooling?RCS,?overfilling?the?Steam?Generator,?increasing?the? pressure?in?the?containment?and?ultimately?causing?an?unnecessary?diesel?generator?capacity.?? It?is?important?to?note,?that?the?EFW?can?also?be?initialized?manually?in?the?case?of?SG? levels?being?deemed?too?low.?The?inserted?water?is?standard?secondary?water?that?is?pumped? through?either?electric?or?steam?turbine?pump.?The?electric?pump?allows?for?more?reliability? whereas?the?steam?turbine?driven?pump?allows?for?decay?heat?removal?during?station?blackout.? For?the?steam?turbine?drive?pumps,?the?pipes?are?designed?to?prevent?the?condensation?of?the? steam?along?the?inside?walls?of?the?pipe.?Additionally,?it?should?be?noted?that?there?is?standard? testing?on?pumps,?valves?and?instrumentation?should?be?regularly?monitored?as?to?prevent?any? abnormal?incidents.?? 2.2.5. Safety?Injection?System?(SIS)? The?overall?function?of?the?SIS,?is?to?maintain?acceptable?boron?concentration?in?the? coolant.?The?SIS?injects?boron?during?cold?core?shutdown?and?during?main?steam?line?breaks.? Furthermore,?it?will?also?used?to?adjust?excessive?boron?levels?seen?in?RCS?levels?in?cold?leg? LOCAs,?to?prevent?possible?boron?precipitation.?During?safe?cool?shutdowns,?the?injection?of? boron?will?taken?from?the?IRWST?to?maintain?safe?shut?down?by?keeping?the?reactor?at? subcritical?levels.?In?the?case?of?a?main?steam?line?break,?the?SIS?will?take?water?from?the? refueling?storage?tank?and?inject?the?coolant?to?maintain?an?dose?limit?within?10?CFR?20?limits.?It? should?be?noted,?that?in?emergencies,?the?SIS?is?capable?of?providing?cooling?during?a?bleed?and? feed?operations.?? 2.2.6. Safety?Depressurization?and?Vent?System? The?SDVS?is?the?system?comprised?of?the?valves?and?piping?that?connects?and?allows?for? the?flow?from?the?pressurized?steam?space?and?reactor?upper?head?to?the?IWRST.?The?SDVS?is?a? general?system?that?is?used?for?the?depressurization?and?venting?of?some?high?pressure?systems.?It? is?designed?to?be?a?safe?and?ultimately?useful?tool?to?eliminate?high?pressure?in?the?RCS.?In?the? case?of?a?transient?loss?of?feedwater?(TLOFW)?the?SDVS?will?trigger?and?will?allow?for?core? 5
- 6. cooling?using?a?single?bleed?path?in?a?2/4?pump?system?and?preventing?immediate?fuel? uncovering.?? The?SIS?is?designed?to?operate?in?any?condition,?excluding?start?up.?It?is?used?mainly?in? standard?operation?and?in?upset?or?accident?scenarios.?Furthermore,?the?valves?in?the?SDVS? should?be?able?to?operate?in?a?blackout,?allowing?for?bleeding.?Ultimately,?the?SDVS?is?not? automatically?actuated,?but?rather?manually?actuated?from?the?control?system.?? 3.0 Evolutionary?Power?Reactor? 3.1 Introduction? The?EPR?is?a?Franco?German?designed?reactor?from?the?companies?of?AREVA,?EDF?and? Siemens.?With?multiple?ERPs?being?built?in?many?countries,?and?with?many?other?countries? verifying?the?design,?the?EPR?is?one?of?the?most?popular?modern?reactor?designs?in?the?world? today.?The?EPR?is?one?of?the?biggest?reactors?under?construction,?with?an?approximate?1650? MWe?and?a?four?loop?safety?system?making?it?a?very?interesting?and?feasible?reactor?under? construction?today.? 3.2 Design?Benefits?? Arguably?the?greatest?advantage?of?the?EPR?design?is?the?four?loop?safety?system.?The?concept? behind?this?design?was?to?create?a?safety?system?with?vast?amounts?of?redundancy.?This?concept? ultimately?brought?about?the?idea?of?have?four?independent?emergency?cooling?systems.?Each?of? the?loops?provides?adequate?decay?heat?removal?for?up?to?1?3?years?after?reactor?shutdown.?? Compared?to?many?PWR,?it?has?reduced?fuel?consumption?allowing?for?easier?system? maintenance.?Additionally,?there?is?a?slightly?higher?thermal?efficiency?with?means?a?reduction?in? water?usage,?but?considering?the?four?cooling?loops,?the?amount?of?water?used?is?still?relatively? similar?to?other?PWRs.?A?very?useful?and?distinct?benefit?to?other?PWRs?is?the?use?of?hydrogen? re?combiners?that?will?minimize?the?possibility?of?hydrogen?explosions?by?a?drastic?margin.?? 3.2.1 Comparison?to?the?AP1000? The?EPR?boasts?some?very?impressive?safety?features,?but?does?have?some?very?important? differences?compared?to?the?AP1000.?In?a?safety?standpoint,?the?core?accident?frequency?of?the? EPR?is?approximately?3.7?*10^?7?(Rx?yr)?while?the?AP1000?boasts?a?core?accident?frequency?of? ~1*10^?6?(Rx?yr).?Although?both?designs?boast?very?low?frequencies,?it?should?be?noted?that?the? NRC¨s?frequency?threshold?is?set?at?10^?4?(Rx?yr)? The?AP1000?operates?with?two?loops,?along?with?a?PRHR?heat?exchanger?which?allows?for? natural?circulation?heat?removal.?The?Passive?Safety?Injection?Systems?includes?Core?Makeup? Tanks,?Accumulators,?IRWST?injection?system?and?a?means?of?automatic?RCS?depressurization.? In?the?case?of?core?meltdown,?the?EPR?uses?the?concept?of?a?｀Core?Catcher¨?while?the?AP1000? keeps?the?corium?in?In?vessel?retention.?? 6
- 7. ? 4.0 Case?1:?Malfunction?in?Feedwater?System?? The?reduction?of?the?feedwater?temperature?causes?the?decrease?of?the?RCS?temperature?which? cause?reactivity?insertion?into?the?core.?The?case?can?occur?at?either?at?Hot?Zero?Power?(HZP)?or? during?Hot?Full?Power?(HFP).?The?HZP?case?is?bound?by?the?HFP,?because?the?load?and? feedwater?flow?is?lower?and?the?variety?rate?of?energy?is?less?at?HZP.?Therefore,?it?is?only? necessary?to?consider?the?reduction?of?the?feedwater?temperature?at?HFP.A?simple?case?was? generated?to?show?the?difference?in?enthalpy?to?analyze?the?excessive?load?increase?in?secondary? steam?flow.?? The?reduction?of?feedwater?enthalpy?could?be?compared?with?the?case?of?excessive?load? increase?in?secondary?steam?flow.?If?the?reduction?of?feedwater?enthalpy?in?the?case?of? malfuction?of?feedwater?system(case?A)?is?less?than?the?reduction?of?feedwater?enthalpy?in?the? case?of?excessive?load?increase?in?secondary?steam?flow(case?B),?The?case?A?is?bounded?by?the? case?B.?The?reduction?of?feedwater?enthalpy?was?calculated?in?the?case?of?excessive?load?increase? in?secondary?steam?flow(case?B)?using?the?initial?conditions?in?Appendix?A.1.?? ? The?following?equation?was?used?to?determine?Heq:? ????Eq.?4.1Sec.?Steam?Enthalpy ec.Feedwater?Enth.) .1 Sec.Steam?Enth. eq) .0?????( ? S * 1 = ( ? H * 1 ? ? The?calculated?enthalpy?was?342?btu/lbm,?demonstrating?a?78?btu/lbm?enthalpy?reduction?in?the? feedwater.?? 5.0 Case?2:?RCS?Boron?Concentration?Design?Transient?? In?the?case?of?a?varied?boron?concentration?in?the?RCS,?the?spray?is?tripped?and?begins?to? process?to?balance?out?the?boron?concentration?between?the?RCS?loop?and?the?Pressurizer.? During?this?scenario,?the?standby?heater?causes?an?increase?in?pressure?inside?the?Pressurizer.?The? pressure?then?reaches?a?set?minimum?pressure?level?in?which?the?spray?is?tripped?therefore? maintaining?the?pressure?inside?the?Pressurizer?at?a?level?proportional?to?the?spray?rate.?After? continued?operation?of?the?spray,?the?boron?concentration?in?the?RCS?loop?and?the?Pressurizer? should?level?off.?This?scenario?can?apply?to?lower?or?higher?levels?of?boron?concentration.?? For?case?2,?the?assumption?that?the?secondary?side?was?not?affected?by?the?transient?was? made.?The?RCS?pressure?will?vary?with?the?pressure?in?the?Pressurizer?as?the?coolant?flowing? from?the?Pressurizer?heats?the?nozzle?of?the?surge?line?connected?to?the?RCS?hot?leg.? ? 7
- 8. ρ h )P = VB * ? * ( f ? hcl Eq?5.1? ? Where P is power, is volumetric flow rate, ρ is the density of the fluid in the spray, is the? ? ? ? VB ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?hcl ? ? enthalpy?of?the?fluid?in?the?cold?leg?and? is?the?unknown?variable.hf ?? Next, the second equation was used to determine the flow rate with the determined pressure of? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? the Pressurizer. Knowing that the pressurizer flow rate is proportional to the maximum and? ? ? ? ? ? ? ? ? ? ? ? ? ? minimum?pressure?values?seen?in?Appendix?B.1.?The?equation?simply?becomes?the?following:? ? ???????????????????????????????????Eq?5.2P ?Pf l V ?VB f B l = P ?Pm l V ?VB m B l ?? Where stands for the volumetric flow rate of the fluid relative to the pressure . The ｀m¨? VB f ? ? ? ? ? ? ? ? ? ? ? ? ? ? Pf ? ? ? and ｀l¨ subscripts indicate the maximum and minimum, for the volumetric flow rate and the? ? ? ? ? ? ? ? ? ? ? ? ? ? ? pressure.?? ? This part of the calculation is where I had problems to resolve the correct values due to lack of? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? resources provided by SNERDI. Based on rough estimations from the NIST tables, and the? ? ? ? ? ? ? ? ? ? ? ? ? ? conservation of energy and mass equations, I was able to determine an estimated saturation of? ? ? ? ? ? ? ? ? ? ? ? ? ? ? pressure of 15.719 MPa with a volumetric flow rate of 13.844 with the heater on? ? ? ? ? ? ? ? ? ? ? /hr?m3 ? ? ? ? ? (1230kW). From this, the maximum temperature reached in the Pressurizer was approximately? ? ? ? ? ? ? ? ? ? ? ? 345 C based on the saturation pressure of 15.719 MPa. Furthermore, it was determined that the? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? estimated saturated enthalpy was ~1230 kJ/kg. The length of time of the entire transient case? ? ? ? ? ? ? ? ? ? ? ? ? ? ? should take ~120 minutes based on the total volume of the Pressurizer and the flow rate out of it? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? (which is the same as the flow rate into the Pressurizer). That¨s the length of time before the? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? water in the Pressurizer is completely replaced and the RCS¨s boron concentration levels are? ? ? ? ? ? ? ? ? ? ? ? ? ? back?at?nominal?conditions.? ? ? ? ? ? ? ? ? ? ? 8
- 9. ? 6.0 Appendix?? ?? A.1?Initial?Conditions?for?the?Feedwater?System?Transiet? ¢ The?secondary?side?steam?enthalpy?is?H?steam?=?1200.0?Btu/lbm?after?the?accident?? ¢ The?secondary?side?feedwater?enthalpy?is?H?feed?=420.0?Btu/lbm?after?the?accident?? ¢ The?normalized?secondary?side?steam?flow?is?R=1.1?after?the?accident?? ¢ The?secondary?side?steam?enthalpy?maintains?the?same?before?and?after?the?accident?? ¢ The?feedwater?flow?maintains?the?same?before?and?after?the?accident.? ? ? B.1?The?initial?conditions?for?the?Boron?Conectration?RCS?Transient:? ¢ Operating?Power?of?Pressurizer?standby?heater:?1230?kW? ¢ Initial?spray?rate?pressure:?15.686?MPa? ¢ Maximum?spray?rate?pressure:?16.065?MPa? ¢ Maximum?spray?rate:?159?m?3? /h? ¢ RCS?cold?leg?temperature:?279.4?C? ¢ RCS?hot?leg?temperature:?322.3?C? ¢ Pressurizer?norminal?water?volume:?28.32?m?3 ? ¢ Setpoint?value?of?low?temperature?alarm?of?spray?pipe:?262.8?C? ¢ Total?volume?of?spray?line:?0.350?m?3 ? ¢ Norminal?Pressurizer?pressure:?15.5MPa? ? The?main?assumptions?for?the?case?were?as?follows:? 1 The parameters on the secondary side are not affected by the transient. The RCS? ? ? ? ? ? ? ? ? ? ? ? ? ? pressure vary with the pressurizer pressure, as the fluid flow from the pressurizer, the? ? ? ? ? ? ? ? ? ? ? ? ? ? heat impact may be caused to the nozzle of pressurizer surge line connect to the RCS? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? hot?leg?? 2 The pressurizer water level is maintained stably, the fluid flow in the surge line equal to? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? the?spray?flow.? ? ? 9
- 10. ???????C.1?Resources? ¢ ＾1.1,?1.2,?4.4,?15."??AP1000?Design?Control?Documents?.?Rev.?19?ed.?6.?Print.? ? ¢ "Design?Certification?Application?Review???U.S.?EPR."??NRC:?.?Web.?17?Aug.?2015.? ? ¢ "International?Atomic?Energy?Agency?|?Atoms?For?Peace."?Web.?17?Aug.?2015.? ? ¢ "NRC:?Home?Page."?Web.?17?Aug.?2015.? 10