EDF R&D program on the ageing of reactor pressure vessel internals

Transcription

1 EDF R&D program on the ageing of reactor pressure vessel internals A. Al Mazouzi EDF R&D, France Page 1 Contact: abderrahim.al-mazouzi@edf.fr

2 Outline 1. EDF R&D / MAI: objectives, members and mission 2. Field experience : bolts cracking 3. Modeling methodology 4. Modeling of Irradiation Assisted Stress Corrosion Cracking 5. Major unknowns and current R&D Programs 6. Conclusions Page 2

3 EDF in brief A global energy leader 37 million customers worldwide 158,842 employees worldwide 65.2 bn turnover, 44.5% of which stems from outside France TWh produced worldwide g CO 2 per kwh produced Key figures Electricity: all operational activities, from production to transmission & distribution and marketing Strong presence in Europe: France, UK, Italy Industrial operator in Asia and the United States Natural gas: a major player Page 3 44 Outside France, o.w. UK 16 Italy Turnover (%) 3 EDF Research & Development May France 2010 Production Mix (Group) (%) 1.3 Other energies 7.9 Hydraulic 5.5 Gas 9.8 Fossil fuels Total: TWh 75.4 Nuclear

4 R&D: top priorities Médiathèque EDF 3 top priorities: Consolidating and developing a decarbonated production mix: Nuclear advantage Development of renewable energies Carbon capture and storage Steering the energy demand: Knowledge of the demand New uses for electricity Smart cities Adapting the electrical system: Management of electrical facilities Development of transmission infrastructures Page 4 Research on electric vehicles: preparation of the elements used in a lithium battery cell

5 R&D: key figures Médiathèque EDF 500 Major research projects per year 486 M 2010 Budget one quarter of which is dedicated to projects with an environmental component Page 5 90% Success rate For annual contracts signed with EDF Group entities and business units

6 R&D: key figures Médiathèque EDF over 2,000 people, including 31% women 370 doctors 220 doctoral students 15 Departments 200 research fellows from Universities and other higher education establishments 2 Mixed research units (LAMSID, IRDEP) 12 Common laboratories 3 International institutes (MAI, ECLEER, EIFER) Page 6 7 Research Centres of which: 3 in France 1 in Germany 1 in the UK 1 in Poland 1 in China

7 About the MAI Page 7 Universities (Michigan, MIT, Tohoku, Manchester, Imperial, Oxford, Rouen, Lille, Paris ), ParisTech (Mines, Ponts, Chimie, Arts & Métiers), INP-Grenoble, INSA de Lyon

8 Major MAI research topics Lifetime of the Reactor Pressure Vessel (RPV) Lifetime of the RPV internal structures Stress Corrosion Cracking of components Thermal & environmental fatigue Secondary circuit management Concrete degradation Cable ageing NDE Page 8

9 Components and materials Lower internals description Formers Former 4m Core Barrel Baffle bolt CW 316 or 316L (17%Cr-11%Ni-2,5%Mo) Baffle plate SA 304L (18%Cr-10%Ni ) bolts 3m Baffle plates Lower Internals Page 9

10 Components and materials role to support the core weight, to maintain the alignment of the fuel assemblies, the control rods and the in-core instrumentation, to channel the coolant fluid flow, to protect the pressure vessel against the core radiations to stay rigid. Baffle plates Baffle bolts to position the control rods in the axis of the fuel assemblies to immobilize the fuel assemblies Page 10

11 Field experience - Chronological account In the 80's: baffle jetting occurred in CP0 reactors. 1988: first ultrasonic inspection of baffle bolts (some cracks were discovered). An inspection programme was scheduled. Some baffle bolts were extracted for metallurgical examinations and the phenomenon was attributed to IASCC. Evolution of the total number of cracked and uninterpretable bolts 120 Page 11 Total number of cracked and uninterpretable bolts Hours BUG2 BUG3 BUG4 BUG5 FES1 FES2

12 Field experience Factorsinfluencingthe extent of bolts cracking Total amount of cracked bolts Irradiation dose: the overall compilation of data shows that there is a threshold for inservice baffle bolt cracking and that the rate of cracking decreases for higher dose window of higher cracking dose threshold decrease in cracking Temperature: Correlation between the temperature calculated and the cracking level per equivalent column location in the reactor (chronological account of temperature between beginning and end of the cycles) Number of Dective Bolts Cumulated dose of the bolt Bolt temperature 1J15 2J15 3J15 1K15 2K15 1L15 2L15 3L15 4L15 1L14 2L14 1M14 2M14 1M13 2M13 Stress Bolt location Material Page 12

13 Design improvement and mitigation measures Measures to reduce stress and temperature: Conversion downflow to upflow design to reduce the differential pressure between the core barrel/baffle plate inter-space and the core itself. Better cooling of the bolts (holes in the formers), Lower torque of the bolts Parabolic-shaped connections of the shanks to the heads, 2000 to 2008 : Functional repairs carried out replacement of bolts New technology EPR : no bolts, no weld but massive internals Solution to all the problems Or New kind of problems? Page 13

14 Field experience How much does itcost? Some figures about bolt replacement : - Development and qualification of UT control methods ~ 1.2M - UT control of the bolts ~ 400 k - Replacement of cracked bolts ~ 2 M - Replacement of the Internals on one PWR ~ 105 M Need of studies to understand and anticipate the problems Page 14

15 EDF R&D methodology Neutronic calculations Deposit Energy Thermo-Hydraulic calculations Gas Production Irradiation Dose Temperatures Materials Materials Properties Constitutive Law IASCC Modelling Mechanical calculations IASCC Initiation Criterion Cracking Risk Analysis Stress Strain Field Experience In Service Inspections Page 15 PERFORM 60 FP7 Project Safety Reports Maintenance Strategy Life Span

16 Mechanical calculations Global model for the deformation of the structure Local model for the stress/strain of the bolts Page 16 dpa T ( C) Stress (MPa)

17 PERFORM 60 FP7 Project Materials ageing: IASCC Page 17 Courtesey: M. Vankeerbergen (SCK.CEN)

18 PERFORM 60 FP7 Project Methodology: integration of modules INPUTS: Microstructure T, ph T, fluence Load Microstructural evolutions: RIS Matrix damage OUTPUTS: Time to initiation Depth of cracking Cracking criteria: True initiation? Crack extension? Plasticity law evolution: Interaction matrix Critical resolved shear stress Page 18 Stress & strain evaluations: Local values Strain localization (clear bands) Stress concentration on GBs Oxidation: Mean & max oxide penetration Metal-oxide interface

19 PERFORM 60 FP7 Project Objectives of the project Deliver descriptive models for irradiation degradation mechanisms relevant to LWR internals: Irradiation Assisted Stress Corrosion Cracking (IASCC) Integrate single phenomenon modules into numerical tools describing SCC and microstructure evolution of irradiated stainless steels Compatibility between modules Top-down approach to focus developments on the needed contribution to end products Verification and Validation of modules Page 19 Focus on industrial relevant materials for final verification The main aim of the MA-project is to provide a chain of codes based on the multi-physics and multi-scale approaches to be able to simulate the behavior of stainless steels, and more especially the initiation of IASCC under PWR conditions,

20 PERFORM 60 FP7 Project Irradiation effect: Microchemical evolution 15 Precipitation Defect clusters 10 5 Precipitate size, nm Dose, dpa Segregation 100 nm Page 20 Nano-cavities: Swelling?

21 PERFORM 60 FP7 Project Modelingof Microstructure & Segregation Tools to build end-products Atomic-level tools to parameterise end-products ab initio potentials & MD elementary properties Inputs and mechanisms to parameterise end-products cascades AKMC and MMC, phase field primary damage mechanisms IRRAD pka spectrum CONVOLVE End-products Microstructure modelling OKMC Rate theory loops & voids density ; size distribution, swelling Segregation SCMF RIS FE source term LONG_TERM clusters distribution f(t) Experimental validations HARD Page τ(t)

22 PERFORM 60 FP7 Project From the evolution of the microstructure to the mechanical properties Physics modeling Irrad. microstructure Mesoscopic scale: DD Crystalline aggregate Mechanics Modeling RVE mechanics 10 nm 5 µm 100 µm CW Hardening Localisation Grain Boundaris Crytal rotation Localisation Page 22 Homogenization micro-meso Homogenization micro-macro Homogenization

23 PERFORM 60 FP7 Project Mechanical fields evaluation The observation of local mechanical fields is a good information to derive identification or to validate a model Displacement and total strain are natural quantities to compare experiments and computations 500 Austenitic stainless steel (316 L) Average Stress (MPa) Image acquisition topography R.O.I L / L 0 In situ sample Page 23 Dimensions in mm

24 PERFORM 60 FP7 Project Flow behavior of irradiated materials Irradiation effect: Adaptation of the crystalline law to integrate irradiation effect 304L Hyp 316 E [Pokor, 2003] Page 24

25 PERFORM 60 FP7 Project Effect of the environment Environment 300 C 1000 ppm B, 2 ppm Li 25 cc H 2 /kg Transport properties Diffusion coefficients Interface rate constants Field strength PD/MCM FEM of oxide formation and vacancy injection Material & Environment Oxide and Oxidation characterization Oxide & Oxidation properties PD/MC, IO model parameterization vacancy & ion flux at M/O interface Material 316 stainless steel Structure & Chemistry M 2 O 3 (x), AB 2 O 4 (x) A(x), B(x), M(x) O(x) AKMC Oxide film properties w/ link to dislocations Vacancy enhanced creep parameterization Corrosion contribution to crack-tip softening Page 25

26 PERFORM 60 FP7 Project Cracking criterion for nonirradiated stainless steel 5 x Mean stress = 563 MPa SD(Eeq) 0,08 0,07 0,06 0,05 0,04 0,03 0,02 0,01 FEM 1 measure/specimen Measures on the same specimen y = 0,3424x R 2 = 0,9382 Frequency Stress to crack GBs = 761 MPa Stress at grain boundaries (MPa) Page 26 0,00 0,00 0,05 0,10 0,15 0,20 Mean(Eeq)

27 PERFORM 60 FP7 Project Methodology: integration of modules INPUTS: Microstructure T, ph T, fluence Load Microstructural evolutions: RIS Matrix damage OUTPUTS: Time to initiation Depth of cracking Cracking criteria: True initiation? Crack extension? Plasticity law evolution: Interaction matrix Critical resolved shear stress Page 27 Stress & strain evaluations: Local values Strain localization (clear bands) Stress concentration on GBs Oxidation: Mean & max oxide penetration Metal-oxide interface

28 PERFORM 60 FP7 Project Example of results No crystal plasticity, 1 µm 3, final el. = 30%, dε/dtdt = s -1 Page 28 Opening stress at grain boundaries

29 PERFORM 60 FP7 Project Multi-Scale Modelling Approach Mechanical fields, corrosion Component behavior h-year Micro-analysis: TAP, TEM, SANS, 0.4 µm Time Finite Elements Mesoscopic (grain, set of grains) Dislocation Dynamics s - h Kinetic Monte Carlo [Rate theory] Classical Molecular Dynamics ns ab initio (Elementary Mecanisms) 0 - ps Page 29 1nn nn 1nm 3 (30-100nm) 3 (10-30nm) 3 µm 3 cm 3 System size

30 Main unknowns from field experience Need of R&D studies Effects of the environment on intergranular cracking Definition of the mechanisms: roles of hardening, Radiation Induced Segregation, Hydrogen? Grain hardening under irradiation, Strain localisation that may lead to stress concentration on the grain boundaries, Segregation on the grain boundaries, Irradiation creep and grain gliding, Weakening by Hydrogen (H from corrosion, transmutation, etc ) Possible precipitation of He bubbles in the grain boundaries, Influence of PWR chemistry Sweeling Principal parameters that can have an influence on the cracking sensitivity (temperature, stress, fluence...)? Threshold for the beginning of the cracking, crack growth rate, saturation level? Effect of the transient on the materials behavior: CIIDS to be launched within NUGENIA... Page 30