Borssele Reactor vessel. Doel-3 phenomenon Inspection at Borssele

Transcription

1 Borssele Reactor vessel Doel-3 phenomenon Inspection at Borssele

2 Introduction Jan van Cappelle Head of Borssele Nuclear Power Plant Responsible for nuclear safety and radiation protection at the Borssele Nuclear Power Plant 2

3 Overview 1. What it is 2. Immediate concern! 3. Clear evidence 4. Proof of the pudding 5. Famous last words 3

4 What it is Doel-3 Phenomenon Let s just refresh our memories again! 4

5 Doel-3 Phenomenon cloud of laminar indications, concentrated in the base material, mostly on the inner side of the forged ring The figure displays a typical example of data recorded in the lower core shell. Left: an axial section, with indications appearing as colour spots. Right: the indications, all detected in a 20 sector of the shell, are cumulated on the figure plane. They appear to be nearly laminar in nature and form a cluster sinking with increasing altitude, from the inner surface up to a depth of approximately 120 mm. Source: Safety case report: Doel 3 reactor pressure vessel assessment, Electrabel. Published on 5

6 Doel-3 Phenomenon What is the Doel-3 phenomenon? US inspection: Large amount of grouped laminar indications, in the base material on the inner side of the ring, oriented more or less parallel to the walls, spread almost evenly all around the circumference of the ring. Origin: If the temperature of the ingot decreases below approximately 200 C before the hydrogen concentration is sufficiently reduced, hydrogen flaking occurs (mainly) at impurities. 6

7 Doel-3 Phenomenon Distinctive characteristics of the Doel-3 phenomenon : large amount of laminar fractures, in the base material, nearly parallel to the walls, distributed almost evenly around the entire circumference, originated during fabrication Conclusion: If any one of these characteristics is not present, then there is no Doel-3 phenomenon 7

8 Actions by EPZ EPZ responses since the Doel-3 phenomenon was related to Borssele s RPV manufacturer Rotterdam Dockyard Co. (RDM)? 8

9 General response Every event at a nuclear power plant initiates a learning process: Own specialists launch an investigation World Association of Nuclear Operators (WANO), the international sector organisation of nuclear power plants established to share knowledge internationally for safe nuclear energy, ensures experiences are shared German association of major electricity producers (VGB) coordinates sharing of experience between nuclear plants supplied by Siemens/KWU 9

10 Immediate Concern! Could the the Doel 3 phenomenon be present in the Borssele reactor pressure vessel? Is the situation in Doel-3/Tihange-2 transferable to Borssele? 10

11 Immediate Actions EPZ specialists compared Doel-3 with Borssele (desk study) Data collection: own archive, Electrabel/Tractebel, Areva, VGB, other NPPs, former RDM epmloyees, Lloyds, Find similarities Find differences Find crack development scenarios Expert evaluation 11

12 Similarities Reactor vessels at Doel-3, Tihange-2 and Borssele are all made of carbon steel Manufacturing of the affected rings in Doel-3/Tihange-2 and the Borssele reactor pressure vessel were all contracted to RDM RDM subcontracted some work: casting by Krupp forging by RDM

13 Differences Borssele had different supplier, with different specifications Siemens/KWU deliberetly specified a different type of carbon steel for Borssele, designed for its resistance against hydrogen flakes Siemens/KWU specified more stringent requirements regarding quantity of hydrogen than ASME prescribed Borssele cast segments were much smaller than Doel/Tihange s Manufacturing documentation for Borssele is complete, it includes all temperature treatments and all inspection reports Krupp and RDM had extensive experience with Borssele-type steel, not with Doel-type steel 13

14 Crack development scenarios Origination of hydrogen flakes well known phenomenon since early days of forged reactor pressure vessels Information on Doel-3 phenomenon consistent with knowledge on hydrogen flaking in large forgings Preconditions to prevent hydrogen flakes well known 14

15 Evaluation Expert evaluation for Borssele RPV: Preconditions to prevent hydrogen flakes met US inspections during manufacturing suitable to detect Doel-3 phenomenon US inspection reports demonstrate the Doel-3 phenomenon was not present Conclusion: Doel-3 situation not transferable to Borssele Therefore no reason to assume Doel-3 phenomenon present in Borssele RPV 15

16 Clear Evidence Borssele reactor pressure vessel free from the Doel 3 phenomenon must be proven Formal evidence required to demonstrate the absence of Doel-3 phenomenon based on facts and an accepted knowledge base 16

17 Dedicated project team Actions More extensive international exchange of information Analysis of manufacturing documentation Formal safety assessment of Borssele reactor vessel Repeat of manufacturing inspection on remaining original material The team also contracted NRG to prepare an inspection on the Doel 3 phenomenon in the next regular outage (April 2013), taken into account knowledge development on the phenomenon 17

18 Manufacturing documentation Borssele manufacturing documentation is complete and fully in order All manufacturing documentation reassessed in Long Term Operations project (2034) Therefore good idea of condition of all vital components This included condition and quality of the reactor pressure vessel Reactor pressure vessel: ASME, with additional S/KWU requirements 4 times 100 % US inspection during manufacturing allmost perfect condition at installation regular inspections since commissioning, ASME+ Borssele vessel is top-quality and in excellent condition 18

19 Manufacturing documentation RDM is main contractor, did not perform all steps We have a very good picture of process associated with Borssele vessel: Who, what, where, why, how Inspections by RDM, S/KWU, TÜV, Stoomwezen Siemens/KWU specification Casting Forging Cladding Welding Pressure test quality control Siemens/KWU supervision ISI 19

20 Conclusions Doel-3 phenomenon not possible in Borssele RPV Type of steel highly resistant against hydrogen flaking Documentation of all stages of manufacturing and of all inspections is complete All preconditions to prevent hydrogen inclusion better than required Rings subjected to 100% inspection after each stage of manufacture (incl. 4 x ultrasound) Doel-3 phenomenon would have been found with detection methods used in 1969; this has been demonstrated on original material Siemens, TÜV and Dutch government (Stoomwezen) checked RDM inspections 20

21 Situation end 2012 EPZ presented Dutch nuclear regulator KFD with convincing evidence that Doel-3 phenomenon is not present at Borssele KFD confirmed evidence Responsible Minister informed the Parliament 21

22 Proof of the pudding But the proof of the pudding is in the eating EPZ announced that evidence will be backed by targeted ultrasonic inspection during next regular outage 22

23 Why an inspection? Obvious concerns at the general public: an inspection was considered the ultimate proof whether Borssele is free from the Doel-3 phenomenon or not Regular reactor pressure vessel inspections were already scheduled for the 2013 outage Preparation was already long under way Amended operating license for Long Term Operation not yet applicable, but it required such an inspection 23

24 How was inspection performed? Considering the characteristics of the Doel-3 phenomenon Large amount of laminar indications in the base material, Oriented nearly parallel to the walls, Spread almost evenly all around the circumference of the ring, an US inspection of a 1m wide vertical band covering all parts is more than sufficient to rule out the presence of the Doel-3 phenomenon The inspection was expanded to 4x 1m wide band, 90 apart 24

25 How was inspection performed? Main coolant pipes Main coolant pipes circular welds, reactor vessel segments Scans of 1 x 8 metres Scans on north, south, east and west sides & base 25

26 How was inspection performed? Ultrasound inspection of reactor vessel wall NRG: qualified and accredited inspection company 6 months of preparation (training and development of equipment, qualification of method and people) Inspection was prepared to be done in the normal 2013 outage 26

27 How was inspection performed? Vessel wall scanner Base scanner 27

28 Inspection Results Findings: Each band was free of any reportable indications Results: Absence of the Doel-3 phenomenon was proven 4 times Conclusion: 100% certainty that Borssele vessel does not have Doel-3 phenomenon 28

29 Guarantees of inspection result NRG works for EPZ Lloyd s works for nuclear regulator KFD Lloyd s supervises NRG on behalf of KFD NRG reports to EPZ Lloyd s verifies results Lloyd s reports to KFD EPZ reports to KFD KFD assesses inspection results KFD reports to Minister of Economic Affairs 29

30 Famous Last Words Communications we can never do it right, but we can easily do it wrong! 30

31 Communication EPZ puts a lot of effort in communicating facts Reliable, verifiable and in an understandable way EPZ granted requests for interviews during entire process Fact sheet on Doel 3 phenomenon and the Borssele reactor pressure vessel Press event at the site of the certified inspection company NRG, that prepared the US equipment for the inspection Inspection preparation and execution filmed and available to the public Q&A s Etc. 31

32 Communication but we ve found ourselves challenged by an unexpected perception of these inspections at the general public! EPZ: we have done 4 times a 100% inspection on the Doel-3 phenomenon. We have covered about 50% of the inner surface to do this. Media, general public: EPZ has inspected only 50%, a random sample, just the areas that were known to be free of cracks, 32

33 Thank you for your attention Zeedijk 32, 4454 PM Borssele Postbus 130, 4380 AC Vlissingen Tel. +31 (0) Website: N.V. Elektriciteits-Produktiemaatschappij Zuid-Nederland EPZ 33

34 Manufacturing inspection 34

35 Testing base scanner How was inspection performed? 35

36 Positioning base scanner How was inspection performed? 36