REACTOR VESSEL ASSESSMENT

Transcription

1 WANO Technical Conference Doel 3-Tihange 2 RPV Issue 1 DOEL 3 TIHANGE 2 REACTOR VESSEL ASSESSMENT TU DELFT 28 JUNE

2 GDF SUEZ KEY FIGURES 90.7 billion in 2011 revenues 218,900 employees Capacity: GW installed 14.8 GW under construction 11 billion in gross investments in 2012 Breakdown by fuel at December 31, 2011 (in TWh)* Breakdown by region at December 31, 2011* Natural gas Biomass and biogas 2.6 Wind power 7 Other TWh 44.5 Nuclear ,8 Hydro power** Coal North America 12.3% Latin America 41.2% Europe 10.4% 20.1% Middle East 11% 5% Australia * Including 100% of the capacity of GDF SUEZ assets regardless of the actual holding rate, exc. International Power. ** Including pumped storage. Asia 3 GDF SUEZ ORGANIZATION GDF SUEZ Management Committee Corporate functions: Finance, RH, Comm, SD, R&D, IT, HSE, etc Nuclear Development Nuclear Safety & Radioprotection Energy International Energy Europe Energy Services Infrastructures Global Gas and LNG Environment North America South America Middle East, Turkey, Africa Asia Australia Electrabel (Tihange/Doel) Synatom Laborelec Tractebel Engineering Fabricom Cofely Axima Cofely Endel Cofely Ineo Omega Concept Transnubel Tecnubel Cofely Services 4 2

3 NUCLEAR FLEET Doel & Tihange PWR 1. Doel MW (2 loop - 75) 2. Doel MW (D1 twin) 3. Doel MW ( 82) 4. Doel MW ( 85) 5. Tihange MW ( 75) 6. Tihange MW ( 83) 7. Tihange MW ( 85) Licensed Westinghouse & Framatome (AREVA) - constructed and operated according to US codes, rules, and standards, transposed to Belgian context 5 REACTOR VESSEL ASSESSMENT Overview Indications June August 2012 Safety assessment September December 2012 Feedback authorities January February 2013 Additional analyses, tests, and inspections February April 2013 Conclusions May June

4 REACTOR VESSEL ASSESSMENT Overview Indications June August 2012 Safety assessment September December 2012 Feedback authorities January February 2013 Additional analyses, tests, and inspections February April 2013 Conclusions May June NUCLEAR SAFETY TOP PRIORITY International knowledge sharing RPV Inspections Doel 3 Periodic Safety Reviews Return on experience France No underclad cracks, but Vessel head top cap Vessel head flange Vessel flange Nozzle shell I/O nozzles Core upper shell Core lower shell Transition ring Vessel bottom cap Carbon steel (200 mm)) Stainless steel cladding (7 mm) Primary water 8 4

5 QUICK REACTION Indications found Notification of authorities FANC, Bel V, AIB Vinçotte Full body inspections Full depth & entire inner surface First diagnosis: hydrogen flaking AREVA Tihange 2 inspections Similar, but less indications Hydrogen flaking, a known metallurgical phenomenon during casting and forging process 9 INDICATIONS Nearly laminar round shaped typical size 10 mm - very thin (1 to 4 µm) ASME XI definitions Indication: response or evidence from the application of a non-destructive examination, an elementary record or set of records indicating the possible presence of a flaw Flaw: an imperfection or unintentional discontinuity that is detectable by a non-destructive examination 10 5

6 REACTOR VESSEL ASSESSMENT Overview Indications June August 2012 Safety assessment September December 2012 Feedback authorities January February 2013 Additional analyses, tests, and inspections February April 2013 Conclusions May June MULTIDISCIPLINARY APPROACH Internal & external expertise Electrabel AREVA Laborelec International Experts Review Electrabel Doel 3-Tihange 2 RPV Assessment International Experts Review Board Nuclear Safety Authorities Review AIB-Vinçotte (AIA) Expert WG1 NDE Expert WG2 Metallurgy/Root Cause FANC Evaluation SCK.CEN Tractebel Engineering Oak Ridge National Lab. Electrabel Nuclear Safety Control Dept. Review International Experts Review Bel V National Scientific Council Review Expert WG3 Structural Integrity Analysis National Scientific Experts Political decision Licensee Regulator 12 6

7 Safety Concern The integrity of the reactor vessel must be maintained during normal and accident conditions in order to guarantee the cooling of the nuclear fuel

8 First of a kind Origin and stability of indications Ultrasonic testing (UT) validation Material characteristics Structural integrity assessment 15 First of a kind Origin and stability of indications UT validation Material characteristics Structural integrity assessment 16 8

9 Root cause analysis confirmed flaking during manufacturing. Flakes Fish-eyes Likely Embrittlement Fabrication Hydrogen defects Casting defects Porosities Solidification cr. Non-metallic incl. Shatter cracks Porosities Tearing inclusions Thermal cracking In-Service Swelling Creep Gas bubbles Forging defects Macrosegregations Excessive work cr. Surface imperfect. Fatigue Cladding related defects Underclad cracking Lamellar tearing Temper embritt. Die related Buckling Corrosion Hydrogen defects Hydrogen flakes Due to insufficient dehydrogenation at the time of ingot pouring and the absence of a compensatory heat treatment just after forging 17 Detailed calculations confirmed stability Mechanism similar to flake formation Hydrogen induced cracking Fatigue Low cycle fatigue possible Ligament cracking Ligament cracking Propagation mechanism Corrosion Swelling Creep Gas bubbles 18 9

10 First of a kind Origin and stability of indications UT validation Material characteristics Structural integrity assessment 23/4/ UT reliable Acoustic beam focusing technique (MIS-B equipment) sound energy concentrated in a restricted volume of the examined material Different depth ranges covered by different UT transducers Qualified weld inspection technique applied to entire vessel wall TRANSITION RING TOOL [Operated by NTERCONTROLE-AREVA INTERCONTROLE picture] 23/4/

11 UT reliable Qualification based on destructive tests 27 samples containing flakes Representative material Conservative dimensioning Samples from a cast piece with similar material and flake characteristics as the Doel 3 and Tihange 2 RPVs 21 First of a kind Origin and stability of indications UT validation Material characteristics Structural integrity assessment 22 11

12 No impact on material characteristics Elaborate testing program 400 representative samples Mechanical and metallurgical AREVA, Laborelec, SCK.CEN Destructive tests confirmed fracture toughness and structure of the material surrounding the flakes 23 First of a kind Origin and stability of indications UT validation Material characteristics Structural integrity assessment 24 12

13 Structural integrity confirmed Deterministic and probabilistic methods developed Three separate assessments: 1. Flaw Acceptance 2. Fracture toughness 3. PTS 25 Structural integrity confirmed Deterministic and probabilistic methods Validation by external experts Confirmation of conservative nature Simulation and modeling confirm that flakes meet acceptance criteria with significant safety margin 26 13

14 REACTOR VESSEL ASSESSMENT Overview Indications June August 2012 Safety assessment September December 2012 Feedback authorities January February 2013 Additional analyses, tests, and inspections February April 2013 Conclusions May June SAFETY CASE SUBMITTED Positive reviews Internal positive advice by SCP / DFC External FANC, Bel V, AIB Vinçotte National & international expert groups 28 14

15 PROVISIONAL EVALUATION REPORT Request for complementary information Safety case report of excellent quality No elements for permanent shutdown Additional information required for restart 29 REACTOR VESSEL ASSESSMENT Overview Indications June August 2012 Safety assessment September December 2012 Feedback authorities January February 2013 Additional analyses, tests, and inspections February April 2013 Conclusions May June

16 Addressing additional requirements Flaking confirmed and fully understood UT inspection valid Affected material sound and good properties Structural integrity demonstrated with significant safety margin Load test reveals no new results 31 Addressing additional requirements Flaking confirmed and fully understood UT inspection valid Affected material sound and good properties Structural integrity demonstrated with significant safety margin Load test reveals no new results 23/4/

17 Flaking confirmed and fully understood Flaking susceptibility model Explaining flaking discrepancy in different components Chemical and micro-fractographic analyses Hundreds of samples Too much hydrogen during fabrication Factors that contribute to creation of H flakes Fruehan s graph 33 Flaking confirmed and fully understood Each and every flaw detected is known exact position in RPV wall maximum dimensions in three orthogonal directions This enables the calculation of different flaw statistics (e.g. D3): average flaw density in first 100mm of lower core shell is 2.1 flaws/litre average distance between flaws is 20.4 mm no correlation between positions and fluence distribution no trend between flaws inclinations and position in 34 17

18 Addressing additional requirements Flaking confirmed and fully understood UT inspection valid Affected material sound and good properties Structural integrity demonstrated with significant safety margin Load test reveals no new results 35 Extending UT validation Additional destructive testing Representative samples Higher tilted flakes (Partially) hidden flakes Correct detection and characterization of all types of indications 36 18

19 Addressing additional requirements Flaking confirmed and fully understood UT inspection valid Affected material sound and good properties Structural integrity demonstrated with significant safety margin Load test reveals no new results 37 Good material properties Complementary tests 172 small and large samples Fracture toughness and tensile tests Material characteristics similar between material with and without flakes Specimen with H-flake for direct measurement of toughness at tip of flake 38 19

20 Addressing additional requirements Flaking confirmed and fully understood UT inspection valid Affected material sound and good properties Structural integrity demonstrated with significant safety margin Load test reveals no new results 39 Structural integrity reconfirmed Complementary elasto-plastic analysis Flakes meet requirements of international codes and standards Large-scale bending and tensile testing Proving conservativeness and appropriateness of the assessment methods Tensile test specimen (25mm diam.) Colored boxes envelope flakes 4-point bending test of bars with hydrogen flakes Failure load >> calculated failure load 40 20

21 Structural integrity reconfirmed Extended flake acceptability analysis Confirming the structural integrity with substantial safety margin Structural integrity reconfirmed ASME defines flaw-screening criterion Acceptable flaw size 2a acc Screening criterion flaw size less than half of 2a acc : harmless Lager: further analysis required Eleven found But all meet acceptability criterion (< 2a acc ) 42 21

22 Addressing additional requirements Flaking confirmed and fully understood UT inspection valid Affected material sound and good properties Structural integrity demonstrated with significant safety margin Load test reveals no new results 43 Additional load test 175 bar abs - RPV temp ca 135ºC Acoustic emission measurements Application of AFIAP best practices guide Applicable to isolated industrial tanks Post-load UT inspections Load test did not reveal any unexpected condition nor induced any flaw evolution 44 22

23 REACTOR VESSEL ASSESSMENT Overview Indications June August 2012 Safety assessment September December 2012 Feedback authorities January February 2013 Additional analyses, tests, and inspections February April 2013 Conclusions May June SAFETY CASE ADDENDUM Conclusion of the Project Team Based on all of the tests, analyses, and inspections, Electrabel is convinced that the structural integrity of the RPVs has been demonstrated and that all safety requirements are met. Electrabel asks for the immediate restart of both units

24 SAFETY CASE ADDENDUM Reviews Internal positive advice by SCP / DFC External FANC, Bel V, AIB Vinçotte National & international expert groups Authorities give go-ahead for restart 17 May SAFE RESTART Doel 3: 3 June 2013 Tihange 2: 7 June

25 NUCLEAR SAFETY TOP PRIOTITY Long term Future RPV inspections Each outage Qualifying the MIS-B UT inspection tool and technique 49 Thank you for your attention 25