Doel 3 & Tihange 2 RPV Flaw Indications. Evaluation by Belgian Safety Authorities. 1. Regulatory Body in Belgium 28/06/2013

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1 Doel 3 & Tihange 2 RPV Flaw Indications Evaluation by Belgian Safety Authorities Doel 3 & Tihange 2 RPV Flaw Indications Evaluation by Belgian Safety Authorities 1. Regulatory Body in Belgium 3. International collaboration - In-service inspections - Origin and evolution of indications - Material properties - Structural integrity of RPV -Load test 5. What s next? 1

2 1. Regulatory Body in Belgium Federal Agency for Nuclear Control Federal: Nuclear = Federal matter Agency: Public Interest Organisation created by law of 15/04/1994 operational since 1/09/2001 Autonomous government institution Governed by Board of Directors and daily management by Director General and Directors 150 employees Nuclear: Nuclear safety, physical protection, nonproliferation, radiation protection (workers, public & environment) Control: Regulating, Licensing, Inspections, Surveillance of radioactivity on Belgian territory Supported by Scientific Council 1. Regulatory Body in Belgium Bel V: Technical Support Organisation of FANC in charge of permanent and periodical control of major nuclear facilities AIB Vinçotte : Follow up of in-service inspections and evaluation of results (ASME Code Section III and XI) 2

3 Doel 3 & Tihange 2 RPV Flaw Indications Evaluation by Belgian Safety Authorities 1. Regulatory Body in Belgium 3. International collaboration - In-service inspections - Origin and evolution of indications - Material properties - Structural integrity of RPV -Load test 5. What s next? Flaw Indications found during 2012 RPV Inservice inspections at Doel 3 & Tihange 2 Safety concern: Is structural integrity of the reactor pressure vessel still maintained at all times and in all circumstances? Source: Electrabel 3

4 3 step approach towards licensee Step 1: Collection of all relevant information (construction file, previous in-service inspections, detailed findings of 2012 in-service-inspection, ) Step 2: Explanation of origin of flaw indications Step 3: Discussion of justification file for possible restart Need to exchange information on international level FANC Technical Coordination Definition of regulatory approach International information exchange Technical meetings with licensee, foreign authorities,... Bel V & AIB-Vinçotte will Evaluate all requested deliverables (construction file, PSI and ISI records, ) (step 1&2) Give technical evaluation of justification file (step 3) Supported by 3 regulatory expert working groups with participants from other nudear safety authorities FANC will also consult Scientific Council : scientific expert working group International review board for an independent evaluation 4

5 Via Techical Secretary Licensee documents Via Technical Secretary Nuclear Safety authorities WG 1 Non-destructive Examination Techniques Via Technical Secretary WG 2 - Metallurgical origin / Root causes of flaw indications WG 3 - Structural mechanics & fracture mechanics justification file National Scientific Expert Group Scientific Council Advice National Scientific Experts International review board Advice International Review Board Evaluation AIB-Vinçotte Evaluation Bel V Advice Scientific Council Decision Political Authorities FANC summary note for political authorities with proposal for decision Final Meeting between WG 1-3, IRB & SC 08-09/01/2013 Doel 3 & Tihange 2 RPV Flaw Indications Evaluation by Belgian Safety Authorities 1. Regulatory Body in Belgium 3. International collaboration - In-service inspections - Origin and evolution of indications - Material properties - Structural integrity of RPV -Load test 5. What s next? 5

6 3. International collaboration Nuclear Safety Authorities Need to exchange information on international level Unique case, limited to Doel 3 and Tihange 2? Impact on other nuclear reactors? 3 working groups with experts from foreign nuclear safety authorities WG 1 : Non-destructive Examination techniques WG 2 : Metallurgical origin / root causes of the flaw indications WG 3: Structural mechanics & fracture mechanics 3. International collaboration Nuclear Safety Authorities Meetings: August & October 2012, January 2013 Participants from Finland, France, Germany, Japan, the Netherlands, South Korea, Spain, Sweden, Switzerland, the United Kingdom and the United States, and by experts from IAEA, OECD/NEA and EC Goals share information and experience between nuclear safety authorities about regulatory approaches and actions; provide technical advice to the Belgian nuclear safety authority (FANC, Bel V, AIB-Vinçotte) 6

7 3. International collaboration Topics discussed Manufacturing practices Indications and inspection results Flaw indications not detected / detectable during manufacturing and pre-service inspections? Laminar flaws? Metallurgical origin of indications Hydrogen flaking theory confirmed as most probable cause? Other causes possible? Evolution of flaw indications? Structural integrity assessment Justification approach (ASME XI) Need for additional inspections Doel 3 & Tihange 2 RPV Flaw Indications Evaluation by Belgian Safety Authorities 1. Regulatory Body in Belgium 3. International collaboration - In-service inspections - Origin and evolution of indications - Material properties - Structural integrity of RPV -Load test 5. What s next? 7

8 Timing June-July 2012: Flaw Indications found at Doel 3 RPV September 2012: Flaw Indications found at Tihange 2 RPV 05/12/2012: Electrabel Safety Cases 30/01/2013: Publication of FANC Provisional Evaluation Report: additional analysis and tests are necessary (16 requirements) February- April 2013: Licensee action plan to fulfill FANC requirements (approved by FANC on 06/02/2013) April 2013 : Electrabel submits Addenda to Safety Cases 17/05/2013: Publication of FANC Final Evaluation Report In service inspections RESULTS OF LICENSEE ACTION PLAN REQUIREMENT ON : CONCLUSION : 1. Clad interface imperfections 2. Non-inspectable areas 3. Identification of potentially unreported higher tilted flaws 4. Indications with 45 T shear wave response 5. Partially hidden indications 6. Inclination of flaws detected by ultrasonic testing 7. Full formal qualification To be achieved by the licensee ASAP after the restart 8

9 In service inspections FANC FINAL CONCLUSIONS* The uncertainties regarding the capability to properly detect and characterize all present flaws have been removed. In particular, the additional validations and tests by the licensee have shown that hidden flaws and higher tilted flaws can be adequately identified and characterized. No critical hydrogen flake type defects are expected in the areas non-inspectable by UT. *Based on Evaluation by AIB-Vinçotte Origin and evolution of the indications RESULTS OF LICENSEE ACTION PLAN REQUIREMENT ON : CONCLUSION : 8. Follow-up in-service inspections To be achieved by the licensee after the restart (during the next planned outage for refuelling) 9

10 Origin and evolution of the indications FANC FINAL CONCLUSIONS Hydrogen flakes most likely origin : number, size, location in zone of macro-segregation, orientation Factors to explain why the hydrogen flaking did not evenly affect all the forged components of the Doel 3 and Tihange 2 RPVs: size of the ingots and the combined sulphur and hydrogen contents. Significant evolution of hydrogen flakes during reactor operation unlikely, but still: follow-up in-service inspections Material properties RESULTS OF LICENSEE ACTION PLAN REQUIREMENT ON : CONCLUSION : 9. Additional characterization of the material mechanical properties 10. Residual hydrogen 11. Irradiation properties To be achieved by the licensee ASAP after the restart 12. Local microscale properties To be achieved by the licensee ASAP after the restart 13. Thermal ageing To be achieved by the licensee ASAP after the restart 10

11 Material properties FANC FINAL CONCLUSIONS The licensee performed additional material tests on H1 nozzle cut-out material from Doel 3 and on materials, with and without flakes, from the AREVA steam generator shell VB-395. Hydrogen flaking affects the mechanical (tensile and fracture toughness) properties of the material by reducing its ductility and increasing its brittleness. However the degradation of the material properties is considered to be sufficiently limited. From additional experimental fracture toughness tests, the 50 C margin on RT NDT considered in the Safety Case is deemed to be conservative. No significant amount of residual hydrogen present inside the flakes. Structural integrity assessment RESULTS OF LICENSEE ACTION PLAN REQUIREMENT ON : 14. Sensitivity study of higher tilted flaws 15. Large scale validation tests CONCLUSION: 11

12 Structural integrity assessment FANC FINAL CONCLUSIONS The use of a screening criterion procedure allows to conclude that the presence of hydrogen-induced flaws in the Tihange 2 and Doel 3 RPV shells has not a significant impact. Large Scale tensile test specimens from the VB-395 shell: requirement for sufficient ductility and sufficient load carrying capacity is satisfied. Two large scale bend tests on specimens from the VB-395 shell: confirmed the conservatism of the calculations with a failure load well above the predicted load. Load Test RESULTS OF LICENSEE ACTION PLAN REQUIREMENT ON : CONCLUSION : 16. Load test with acoustic emission monitoring and subsequent UT inspection Source: Electrabel 12

13 Load Test During load test : acoustic emission monitoring No evolution Post load test : UT-inspection No evolution Matching of indications Source: Electrabel Load Test FANC FINAL CONCLUSIONS The load-tests that were performed on the Tihange 2 and Doel 3 reactor pressure vessel did not reveal any unexpected conditions. The results from the acoustic emission measurements performed did not reveal any critical source of area where supplementary investigations are mandatory. The post-load test ultrasonic testing inspections in 2013 confirmed that there was no evolution of the flaws induced by the load test. Both the number of indications, the amplitude and the dimensions of each indications are consistent with the results of the ultrasonic inspection testing in September

14 Final Conclusions 16 REQUIREMENTS OF PROVISIONAL EVALUATION REPORT: 11 are resolved 5 to be achieved by the licensee after the restart The FANC together with Bel V and AIB-Vinçotte have confirmed that all the safety concerns at the origin of the short-term requirements have been solved in a satisfactory manner. As a consequence, the FANC considers that the Doel 3 and Tihange 2 reactor units can be restarted safely. Final Conclusions SPECIFIC RESTART PLAN : the possible impact of extended shutdown on maintenance and surveillance activities the assessment of safety related systems which were not used or let in a dormant state during shutdown and the associated pre-operational startups tests the possible staffing issues the possibly observed unexpected degradation mechanisms or underestimated rate of degradation the possible specific organization that will be put in place to manage the restart operations a specific inspection during the restart and after the restart of the units 14

15 Doel 3 & Tihange 2 RPV Flaw Indications Evaluation by Belgian Safety Authorities 1. Regulatory Body in Belgium 3. International collaboration - In-service inspections - Origin and evolution of indications - Material properties - Structural integrity of RPV -Load test 5. What s next? DOEL NPP 2 1 Doel 3 : 100% power on 09/06 (1 year shutdown) Tihange 2 100% power on 11/06 (9 months shutdown) 1 TIHANGE NPP 30 15

16 5. What s next? Follow-up of long-term actions Inspections of other Belgian RPVs (Tihange 1, Tihange 3, ) Identical RPV inspections (100%) after 1 year operation of Doel 3 & Tihange 2 Workshop to inform foreign regulators (September 2013) WENRA Recommendations (Europe) More information FANC-website Questions? 16