EDF 3-loop RPV life management beyond 40 years of operation - PowerPoint Presentation

1. EDF 3-loop RPV life management beyond 40 years of operation S. VIDARD (EDF / SEPTEN) - N. JARDIN (EDF / UNIE) - A.M. DONORE (EDF / R&D)4th PLiM conferenceLyon, october 2017

2. SummaryEDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017Management of nuclear components ageingApplication to 3-loop RPV (900 MWe fleet)Focus on two ageing mechanismsThermal ageing of RPV outlet nozzlesIrradiation ageing of RPV beltline regionConclusion

3. Management of nuclear components ageingAgeing management process is part of EDF Long Term Operation (LTO) policyThe process applies to safety-related components (mechanical, electrical, civil works,…) whose failure would affect the plant safety  summary :Selection of safety-related structures / components concerned by ageing mechanismsFor each area of component / structure : identification of potentially relevant ageing mechanisms (depending on material, operating conditions, OPEX feedback,…)Actions demonstrating that each ageing mechanism is properly managed : in-service inspection / surveillance, repair / replacement programmes, supporting R&D ageing programmesPeriodic reviews to include new OPEX feedback, additional results on ageing mechanisms, etc… Process is of course applied to RPVsEDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017

4. Application to 3-loop RPV (900MWe fleet)General presentation of componentMain material = low alloy Cr-Ni-Mo steel (A508 cl.3 type) – inner surface cladded with austenitic steelOther materials = base-nickel alloy (radial guides, CRDM adaptors, bottom-mounted instrumentation penetrations)Main dimensions : total weight = 350t / inner diameter = 4m / thickness in active core region = 200mmMain manufacturing features :Flanges, cylindrical shells, transition ring, nozzles : forged from solid ingotsSpherical shells : laminated plates or forged from solid ingotsWelds of main body : all circumferential (or set-in for nozzles) + austenitic stainless steel DWMsCircumferential weldsSet-in nozzle weldsSS-DWM weldsBase-nickel alloy 600Base-nickel alloy 690EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017

5. Application to 3-loop RPV (900MWe fleet)Identification of main relevant ageing / degradation mechanisms ? Component subject to cyclic loading conditions  evaluation of fatigue riskDifferent types of materials and specific environmental conditions  evaluation of corrosion risk : stress corrosion cracking, intergranular corrosion cracking, atmospheric corrosion, acid boric corrosion,…Component operating at high temperature  evaluation of thermal ageingComponent partially affected by irradiation from reactor core  evaluation of irradiation ageing (neutron flux) 29 [ageing mechanism / area] couples selected for analysis (covering 7 different mechanisms and 18 areas)EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017

6. Application to 3-loop RPV (900MWe fleet)Conclusions on the identified couples ageing mechanisms / areasIn most cases :Either the ageing mechanism on the area is not confirmed by experience, in-service inspection or R&D programmesOr the area can be repaired or replaced with « reasonable » difficulty The ageing mechanism is controlledFor two specific cases (thermal ageing of outlet nozzles and irradiation ageing of beltline region) :The mechanism on the area is confirmedAnd the area cannot be repaired or replaced (or with excessive difficulty) The ageing mechanism requires specific attentionEDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017

7. Focus on two ageing mechanismsMost significant damageing mode for outlet nozzles / beltline region : fast fractureRequirement for fast fracture analysis : « loading of potential crack remains lower than material resistance at all times »  illustration EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017Crack loading : depending on crack dimensions, thermohydraulic transient,… (not affected by the considered ageing mechanisms)Material resistance : depending on metal temperature and a specific material property (RTNDT) For both mechanisms, effect of ageing = RTNDT shift (embrittlement)

8. Focus on two ageing mechanismsThermal ageing of RPV outlet nozzlesWhy only the outlet nozzles ?  operating temperature higher than the other areas of RPV (320°C instead of 285°C)Evaluation of embrittlement due to thermal ageing (RTNDT shift) : predictive model depending on material phosphorus content, operating temperature and time (« McLean model »)Embrittlement initially evaluated for 40 years of operationDemonstration of the model validity for 60 years of operation  supporting R&D experimental programme (see paper # 094)Results : confirmation of the model’s conservatism for 60 years operation  update of mechanical properties uses as input data for mechanical calculation (fast fracture analyses)EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017

9. Focus on two ageing mechanismsThermal ageing of RPV outlet nozzlesIllustration of embrittlement predictions : 40 years vs. 60 yearsEDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017Two types of materials concernedBase metal : limited additional RTNDT shift between 40y and 60y (≤ 3°C)HAZ : additional shift between 40y and 60y ≤ 10°C  the impact of +20 years remains limited, thanks to limited phosphorus content

10. Focus on two ageing mechanismsThermal ageing of RPV outlet nozzlesOther supporting actions for integrity demonstration of outlet nozzlesUpdate of design analyses (RCC-M)Update of fast fracture analyses (RSE-M), with material properties at end of life (60 years)Fatigue evaluation (usage factor, crack growth) with 60 year cyclic loadingsIn-service inspection programme (based on previous inspection results and manufacturing conditions) during 10-year outagesEDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017

11. Focus on two ageing mechanismsIRRADIATION ageing of RPV BELTLINE REGIONEDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017Concerned area = beltline regionShells and weld(s) facing the coreFluence at end of life > 1018 neutron/cm²Effect of irradiation = embrittlement (RTNDT shift) depending on :Chemical content of material (copper, phosphorus, nickel)Irradiation level (fluence, in neutron/cm²)Particular ageing mechanism, subject to mandatory requirements (including specific monitoring of material properties)

12. Focus on two ageing mechanismsIRRADIATION ageing of RPV BELTLINE REGIONKey factor of irradiation ageing = neutron fluence  « the lower, the better »EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017Fuel assemblies equipped withHafnium rods (4 x 3)Fluence = [neutron flux] x [time]Limitation of fluence  limitation of embrittlement[time] parameter : the longer, the better  need to reduce the neutron fluxTwo steps of improvement :1st step in the 90s : modification of fuel assemblies pattern  40% reduction of maximum neutron flux2nd step at 4th 10-year outage : insertion of hafnium rods (neutron absorbers) in specific fuel assemblies  up to 45% additional reduction expectedInsertion of hafnium rods forecasted in all 900MWe RPVs

13. Focus on two ageing mechanismsIRRADIATION ageing of RPV BELTLINE REGIONIllustration of efforts on neutron flux reduction EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017Impact of optimizations on neutron flux shape  maximum effect around azimuth 0°Impact of optimizations on fluence  reduction up to 40% compared to design scenario

14. Focus on two ageing mechanismsIRRADIATION ageing of RPV BELTLINE REGIONMonitoring of RPV material properties : Irradiation Surveillance Programme (ISP)EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017capsule n°2capsule n°4capsule n°3capsule n°1capsule n°5capsule n°6Content / objectives of ISP for each RPV :Material specimens machined from acceptance rings / test coupons  usually 6 capsules / RPVCapsules periodically withdrawn to test materials  measurement of irradiation effect on material properties (RTNDT shift)Capsules irradiated faster than RPV  anticipated knowledge of materiel propertiesRequirement : each capsule at least equivalent to RPV irradiation reached at 10-year outages (1st to 6th)

15. Focus on two ageing mechanismsIRRADIATION ageing of RPV BELTLINE REGIONResults acquired so far :Capsules 1 to 4 extracted, irradiation beyond 60 years already reached for several capsulesIncoming results for capsules 5 and 6  irradiation significantly greater than RPVs after 60 years of operationEDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017

16. Focus on two ageing mechanismsIRRADIATION ageing of RPV BELTLINE REGIONUse of ISP results : Improvement of embrittlement model by fitting predictive formula on ISP results (capsules 1 to 4) and experimental dataComparison of new capsules results with predictive model to check the material behaviourConfirmation / improvement of embrittlement model at higher fluences with incoming resultsEDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017

17. Focus on two ageing mechanismsIRRADIATION ageing of RPV BELTLINE REGIONEDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017Other supporting actions for integrity demonstration of nozzlesUpdate of fast fracture analyses, with material properties at end of life (60 years)Fatigue evaluation (crack growth) with 60 year cyclic loadingsImplementation of new methodologies (Warm Pre-Stressing, thermohydraulical models,…) supported by R&D programmesComplete in-service inspection of beltline region during 10-year outages with automated machine (« MIS »), with qualified NDT

18. ConclusionThe ageing management process implemented by EDF as part of LTO policy, is applied to RPV and periodically reviewedAnalysis of relevant ageing mechanisms for RPV shows that most of them are controlled through usual maintenance policy, including adequate in-service inspectionsTwo mechanisms require particular attention, and are supported by specific actions :Thermal ageing (RPV nozzles), supported by R&D programme to provide adequate predictions of ageing mechanism on material properties for 60 years of operationIrradiation ageing (beltline region), supported by RPV-specific monitoring of material properties, and controlled by inserting hafnium rods to reduce neutron flux (starting from 4th 10-year outages)The performed analyses and implemented actions provide good confidence for 3-loop RPV operation beyond 40 yearsEDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017

19. Thank youfor your attention

20. Appendices900MWe fleet = 34 plantsRPV in French NPP Main Coolant System (MCS)EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017Typical layout of MCS in French NPPs :Originally Westinghouse license3 primary loops / Steam Generators / Main Coolant Pumps1 pressurizer connected to Loop 1 through a surge lineRPV located a the center of the MCS and containment building

21. Illustration on significant ageing mechanisms + preventive / corrective actions EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017Fatigue of studs / nuts / flanges  evaluation of usage factor and adequate in-service inspectionAtmospheric corrosion of stainless steel DWMs  specific in-service inspection on repaired areas + risk eliminated by modification of insulationIrradiation ageing of low-alloy steel (shells and welds)  in-service inspection of beltline region, surveillance programme of material properties, ageing effects included in integrity analysesSCC of CRDM adapters  risk eliminated with RPV head replacement on all plants (use of alloy 690)Thermal ageing of low-alloy steel  relevant only on outlet nozzles (higher temperature), adequate in-service inspection, supporting experimental programme for ageing prediction, ageing effects included in integrity analysesSCC of bottom mounted penetrations (alloy 600)  adequate in-service inspection and development of repair processAppendicesExamples of identified ageing mechanisms

22. AppendicesRPV mechanical analysesDesign analyses : according to RCC-M volume B ( ASME class 1) + updated every 10 year (mandatory)Damageing modes : excessive deformation, plastic instability, progressive deformation, fatigue crack initiation and fast fractureFast fracture (usually « limiting damage » for LTO) :In active core region (= fluence > 1018 n/cm² at EOL)Out of active core region : all welds (including DWM), base metal of thick areas (flanges, nozzle shell, bottom transition ring), studsApplied requirements during operation : RSE-M + French Order 10th november 1999EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017

23. AppendicesRPV in-service inspectionInspection : during 10-year outages, mostly with an automated machine (« MIS »)Systematically inspected areas :UT : all welds of main body (+ RT / PT on DWMs)UT : base metal / weld in active core regionOther inspected areas :UT : nozzles corners and inner surface, RPV head weldUT : nozzle shell (sampling)UT + eddy currents : bottom mounted instrumentation penetrationsEddy currents : studs and nuts, CRDM adapters (sampling)EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017