doel 3 & tihange 2 rpv flaw indications evaluation by ... · pdf filerpv flaw indications...

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Doel 3 & Tihange 2 RPV Flaw Indications

Evaluation by BelgianSafety Authorities

28-06-2013

2013-06-28 Doel 3 & Tihange 2 RPV Issue

Doel 3 & Tihange 2 RPV Flaw IndicationsEvaluation by Belgian Safety Authorities


1. Regulatory Body in Belgium2. Regulatory Approach 3. International collaboration4. FANC Final Evaluation Report

- In-service inspections- Origin and evolution of indications- Material properties- Structural integrity of RPV- Load test

5. What’s next?

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• 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, non-proliferation, radiation protection (workers, public & environment)

• Control: Regulating, Licensing, Inspections, Surveillance of radioactivity on Belgian territory

Supported by Scientific Council

1. Regulatory Body in BelgiumFederal Agency for Nuclear Control


• 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 andevaluation of results (ASME Code Section III and XI)

1. Regulatory Body in Belgium


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1. Regulatory Body in Belgium

2. Regulatory Approach 3. International collaboration4. FANC Final Evaluation Report


5. What’s next?

2. Regulatory Approach

• Flaw Indications found during 2012 RPV In-service 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

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• 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 internationallevel



• 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 participantsfrom other nudear safety authorities

• FANC will also consult – Scientific Council : scientific expert working group– International review board for an independent evaluation


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National Scientific Expert Group

Scientific Council

Decision Political Authorities

Evaluation AIB-Vinçotte

Advice International Review Board

Advice National Scientific Experts

FANC summary note for political authorities with

proposal for decision

Evaluation Bel V

WG 1 – Non-destructive Examination Techniques

WG 2 -– Metallurgical origin / Root causes of

flaw indications

WG 3 - Structural mechanics & fracture

mechanics – justification file

Nuclear Safety authorities

Advice Scientific Council

International review board

Licensee documents

Via Technical Secretary

Via Technical Secretary Via Techical Secretary

Final Meeting between WG 1-3, IRB

& SC08-09/01/2013




1. Regulatory Body in Belgium2. Regulatory Approach

3. International collaboration4. FANC Final Evaluation Report


5. What’s next?

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3. International collaborationNuclear 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 safetyauthorities– WG 1 : Non-destructive Examination techniques – WG 2 : Metallurgical origin / root causes of the flaw

indications– WG 3: Structural mechanics & fracture mechanics


3. International collaborationNuclear 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)


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3. International collaborationTopics 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




1. Regulatory Body in Belgium2. Regulatory Approach 3. International collaboration

4. FANC Final Evaluation Report- In-service inspections- Origin and evolution of indications- Material properties- Structural integrity of RPV- Load test

5. What’s next?

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4. FANC Final Evaluation ReportTiming

• 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


4. FANC Final Evaluation ReportIn service inspections


REQUIREMENT ON : CONCLUSION :

1. Clad interface imperfections

2. Non-inspectable areas

3. Identification of potentially unreported highertilted 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 licenseeASAP after the restart

RESULTS OF LICENSEE ACTION PLAN

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4. FANC Final Evaluation ReportIn 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-inspectableby UT.

*Based on Evaluation by AIB-Vinçotte2013-06-28 Doel 3 & Tihange 2 RPV Issue

4. FANC Final Evaluation ReportOrigin and evolution of the indications



8. Follow-up in-service inspections To be achieved by the licensee after the restart (during the next planned

outage for refuelling)


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4. FANC Final Evaluation ReportOrigin 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 operationunlikely, but still: follow-up in-service inspections


4. FANC Final Evaluation ReportMaterial properties



9. Additional characterization of the materialmechanical properties

10. Residual hydrogen

11. Irradiation properties To be achieved by the licenseeASAP after the restart

12. Local microscale properties To be achieved by the licenseeASAP after the restart

13. Thermal ageing To be achieved by the licenseeASAP after the restart


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4. FANC Final Evaluation ReportMaterial properties

FANC FINAL CONCLUSIONSThe 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 RTNDT considered in the Safety Case is deemed to be conservative.

• No significant amount of residual hydrogen present inside the flakes.…


4. FANC Final Evaluation ReportStructural integrity assessment


REQUIREMENT ON : CONCLUSION:

14. Sensitivity study of higher tilted flaws

15. Large scale validation tests


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4. FANC Final Evaluation ReportStructural 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.


4. FANC Final Evaluation ReportLoad Test



REQUIREMENT ON : CONCLUSION :16. Load test with acoustic emission monitoring and subsequent UT inspection

Source: Electrabel

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During load test : acousticemission monitoring No evolution

Post load test : UT-inspection No evolution Matching of indications

2012-2013

Source: Electrabel


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 2013.


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4. FANC Final Evaluation ReportFinal Conclusions

16 REQUIREMENTS OF PROVISIONAL EVALUATION REPORT:

11 are resolved5 to be achieved by the licensee after the restart

The FANC together with Bel V and AIB-Vinçotte haveconfirmed that all the safety concerns at the origin of theshort-term requirements have been solved in a satisfactorymanner.As a consequence, the FANC considers that the Doel3 and Tihange 2 reactor units can be restartedsafely.


4. FANC Final Evaluation ReportFinal 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 start-ups 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


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1. Regulatory Body in Belgium2. Regulatory Approach 3. International collaboration4. FANC Final Evaluation Report


5. What’s next?

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3

Tihange 2100% power on 11/06(9 months shutdown)

4

DOEL NPP

1

2

3

Doel 3 :100% power on 09/06(1 year shutdown)

TIHANGE NPP


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5. What’s next?

• Follow-up of long-term actionsInspections 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 informationFANC-website

Questions?


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