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 conference
Lyon, october 2017

2. Summary Management of nuclear components ageing
Application to 3-loop RPV (900 MWe fleet)
Focus on two ageing mechanisms
Thermal ageing of RPV outlet nozzles
Irradiation ageing of RPV beltline region
Conclusion
EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017

3. Management of nuclear components ageing
Ageing management process is part of EDF Long Term Operation (LTO) policy
The 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 mechanisms
For 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 programmes
Periodic reviews to include new OPEX feedback, additional results on ageing mechanisms, etc…
 Process is of course applied to RPVs
EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017

4. Application to 3-loop RPV (900MWe fleet)
Circumferential welds
Set-in nozzle welds
SS-DWM welds
Base-nickel alloy 600
Base-nickel alloy 690
General presentation of component
Main material = low alloy Cr-Ni-Mo steel (A508 cl.3 type) – inner surface cladded with austenitic steel
Other 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 = 200mm
Main manufacturing features :
Flanges, cylindrical shells, transition ring, nozzles : forged from solid ingots
Spherical shells : laminated plates or forged from solid ingots
Welds of main body : all circumferential (or set-in for nozzles) + austenitic stainless steel DWMs
EDF 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 risk
Different 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 ageing
Component 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 / areas
In most cases :
Either the ageing mechanism on the area is not confirmed by experience, in-service inspection or R&D programmes
Or the area can be repaired or replaced with « reasonable » difficulty
 The ageing mechanism is controlled
For two specific cases (thermal ageing of outlet nozzles and irradiation ageing of beltline region) :
The mechanism on the area is confirmed
And the area cannot be repaired or replaced (or with excessive difficulty)
 The ageing mechanism requires specific attention
EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017

7. Focus on two ageing mechanisms
Most significant damageing mode for outlet nozzles / beltline region : fast fracture
Requirement for fast fracture analysis : « loading of potential crack remains lower than material resistance at all times »  illustration
Crack 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)
EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017

8. Focus on two ageing mechanisms Thermal ageing of RPV outlet nozzles
Why 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 operation
Demonstration 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 mechanisms Thermal ageing of RPV outlet nozzles
Illustration of embrittlement predictions : 40 years vs. 60 years
Two types of materials concerned
Base 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
EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017

10. Focus on two ageing mechanisms Thermal ageing of RPV outlet nozzles
Other supporting actions for integrity demonstration of outlet nozzles
Update 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 loadings
In-service inspection programme (based on previous inspection results and manufacturing conditions) during 10-year outages
EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017

11. Focus on two ageing mechanisms IRRADIATION ageing of RPV BELTLINE REGION
Concerned area = beltline region
Shells and weld(s) facing the core
Fluence at end of life > 1018 neutron/cm²
Effect 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)
EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017

12. Fluence = [neutron flux] x [time]
Focus on two ageing mechanisms IRRADIATION ageing of RPV BELTLINE REGION
Key factor of irradiation ageing = neutron fluence  « the lower, the better »
Fluence = [neutron flux] x [time]
Limitation of fluence  limitation of embrittlement
[time] parameter : the longer, the better  need to reduce the neutron flux
Two steps of improvement :
1st step in the 90s : modification of fuel assemblies pattern  40% reduction of maximum neutron flux
2nd step at 4th 10-year outage : insertion of hafnium rods (neutron absorbers) in specific fuel assemblies  up to 45% additional reduction expected
Insertion of hafnium rods forecasted in all 900MWe RPVs
Fuel assemblies equipped with
Hafnium rods (4 x 3)
EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017

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

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

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

16. Focus on two ageing mechanisms IRRADIATION ageing of RPV BELTLINE REGION
Use of ISP results :
Improvement of embrittlement model by fitting predictive formula on ISP results (capsules 1 to 4) and experimental data
Comparison of new capsules results with predictive model to check the material behaviour
Confirmation / improvement of embrittlement model at higher fluences with incoming results
EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017

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

18. Conclusion
The ageing management process implemented by EDF as part of LTO policy, is applied to RPV and periodically reviewed
Analysis of relevant ageing mechanisms for RPV shows that most of them are controlled through usual maintenance policy, including adequate in-service inspections
Two 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 operation
Irradiation 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 years
EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017

19. Thank you
for your attention

20. Appendices 900MWe fleet = 34 plants
RPV in French NPP Main Coolant System (MCS)
Typical layout of MCS in French NPPs :
Originally Westinghouse license
3 primary loops / Steam Generators / Main Coolant Pumps
1 pressurizer connected to Loop 1 through a surge line
RPV located a the center of the MCS and containment building
EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017

21. Appendices Examples of identified ageing mechanisms
Illustration on significant ageing mechanisms + preventive / corrective actions
Fatigue of studs / nuts / flanges  evaluation of usage factor and adequate in-service inspection
Atmospheric corrosion of stainless steel DWMs  specific in-service inspection on repaired areas + risk eliminated by modification of insulation
Irradiation ageing of low-alloy steel (shells and welds)  in-service inspection of beltline region, surveillance programme of material properties, ageing effects included in integrity analyses
SCC 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 analyses
SCC of bottom mounted penetrations (alloy 600)  adequate in-service inspection and development of repair process
EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017

22. Appendices RPV mechanical analyses
Design 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 fracture
Fast 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), studs
Applied requirements during operation : RSE-M + French Order 10th november 1999
EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017

23. Appendices RPV in-service inspection
Inspection : 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 region
Other inspected areas :
UT : nozzles corners and inner surface, RPV head weld
UT : nozzle shell (sampling)
UT + eddy currents : bottom mounted instrumentation penetrations
Eddy currents : studs and nuts, CRDM adapters (sampling)
EDF 3-loop RPV life management beyond 40 years of operation | PLIM Lyon - October 2017