RPV DESIGN. FABRICATION AND MATERIALS

Transcription

1 RPV DESIGN. FABRICATION AND MATERIALS Marta Serrano. CIEMAT IAEA Training Workshop on Assessment of Degradation Mechanisms of Primary Components in Water Cooled Nuclear Reactors: Current Issues and Future Challenges CIEMAT, 29 September 2 October 2014

2 CONTENTS Introduction Design Fabrication Materials Large forgings

3 Introduction RPV Dimensions Height =10-20 m Wall thickness = cm Inner diameter= 4-5 m Operational conditions The normal operating pressure is MPa for PWRs and 7-8 MPa for BWRs. The maximum coolant temperature is about 330 C. Radiation environment 40 years

4 RPV - Introduction RPV design process includes a variety of different tasks - Generic Specification of initial material properties Reliable determination of material properties and the pressure and state of flaws in the component Determination of loading (operating, service) conditions Time dependent degradation under service conditions Surveillance of material and flaw state as well as monitoring the service conditions J. Fohl 1998

5 RPV - Introduction Nuclear Irradiation damage, In service inspections, 40 years of operation, Material qualifications TIME (TECNATOM) Ultrasonic and visual RPV designer

6 Design - Stress analysis In general the RPV is made by the welding or joining of different parts: Upper head and flange Nozzle shell course Intermediate cylindrical shells Botton head Different thickness and stress requirements Design Codes (ASME, RCC-M, KTA,..) IAEA No. NP-T-3.11

7 Design - Stress analysis Elastic analysis of stresses: Pressure stress: beltline cylinder, lower head hemisphere, and closure head hemisphere (away from joints with adjacent regions in beltline cylinder) Thermal stress: thick portion of the nozzle shell course region adjacent to a main coolant pipe penetration Discontinuity stress: joints between beltline cylinder and lower head hemisphere, between beltline cylinder and nozzle shell course region cylinder, and between closure head and the closure flange IAEA-TECDOC-1556

8 Design - Stress analysis Classification of stresses (relative to the thickness of the shell) Primary membrane stress, and bending stress, secondary stress (Q), local primary membrane stress, peak stress (F)

9 Design - Fatigue analysis Peak stress: For each load set, an individual fatigue usage factor is determined by the ratio of the number of cycles anticipated during the lifetime of the component to the allowable cycles. The design code specify fatigue design curves that define the allowable number of cycles as a function of applied stress amplitude. The cumulative usage factor (CUF) is the sum of the individual usage factors, and the Codes usually requires that the CUF at each location must not exceed 1.

10 Integrity is assured by a fracture mechanics approach Design - against non-ductile fracture Defects are allowed Critical size Safe operation = Not brittle fracture K I < K IC Design and analysis against non-ductile failure (heatup and cooldown limit curves or normal operation) 2K IM +K IT <K IR where K IM is the stress intensity factor for primary stresses, and K IT is the stress intensity factor for secondary stress

11 Design - against non-ductile fracture

12 RPV MATERIAL

13 Material Design objectives; Strong material High toughness Low brittle transition Assurance of zero defects Long life ~60 years Material selection: generic Availability Strength Durability Cost Formability J. Fohl 1998

14 Material Low alloy steels exhibit a ductile-to-brittle transition which would suggest that they are unsuitable for high-integrity applications; However, the high level of toughness achieved in the ductile failure region for the relatively low cost of the material provides a substantial driver for there use.

15 Material Typical RPV Steels Mn-Mo (SA302B, 20MnMo55) Mn-Mo-Ni (SA302Bmod, SA533 B1) Ni-Mo-Cr (SA508C2, 22NiMoCr36, 22NiMoCr37) Mn-Mo-Ni (SA508C3, 20MnMoNi55, 16MnD5, 18MnD5) Cr-Mo-V (15KhMFA) Ni-Cr-Mo (15Kh2NMFA) Ni Mn Si Mo V Cr Cu P Min Max Min Max Min Max Min Max Min Max Min Max Max Max A302 B 1,15 1,50 0,15 0,30 0,45 0, ,035 A 533 B1 0,40 0,70 1,15 1,50 0,15 0,40 0,45 0, ,035 A 508 C2 0,50 0,90 0,50 1,00 0,15 0,40 0,55 0,70 0,05 0,25 0,45 0,15 0,015 A 508 C3 0,40 1,00 1,20 1,50 0,15 0,40 0,45 0,60 0,05 0, MND5 0,50 0,80 1,15 1,60 0,10 0,30 0,43 0,57 0,02 0,20 0,020 20MnMoNi55 0,50 0,80 1,20 1,50 0,15 0,30 0,40 0,55 0,02 0,20 0,12 0,012 22NiMoCr37 0,60 1,20 0,50 1,00 0,15 0,35 0,60 0,02 0,25 0,50 0,12 0,012 15Kh2MFA 0,40 0,30 0,60 0,17 0,37 0,60 0,80 0,25 0,35 2,50 3,00 0,025 15Kh2MFAA 0,40 0,30 0,60 0,17 0,37 0,60 0,80 0,25 0,35 2,50 3,00 0,08 0,012 15Kh2NMFA 1,00 1,50 0,30 0,60 0,17 0,37 0,50 0,70 0,10 1,80 2,30 0,020 15Kh2NMFAA 1,00 1,50 0,30 0,60 0,17 0,37 0,50 0,70 0,10 1,80 2,30 0,08 0,010

16 Material Plates: SA-302, Grade B: Mn-Mo plates used in the 60 s. German designation 20MnMo55. SA-302, Grade B Mod: The addition of Ni (0,4-0,7 %) to SA-302B increase the strength, so larger vessel can be designed. SA-533 Grade B class 1 Forgings SA-508 Clase 2 German designation 22NiMoCr36 ó 22NiMoCr37. SA-508 Clase 3, higher manganese content, lower molybdenum, and slightly lower C. German designation 20MnMoNi55, french designation 16 MnD5 and 18MnD5. WWER steels The use of forgings reduce the number of welds

17 Material Chemical composition is a key issue for radiation embrittlement Strength increase with Ce=C+Si/24+Mn/6+Ni/40+Cr/5+Mo/4+V/14 C: Cementite improve hardness and strength of steel but decrease toughness properties. Should maintain to the minimum level needed to achieve the desired strength. Si: Silicon is used as deoxidizers. Improve the transition temperature Mn: Manganese is also use as deoxidizer, and improved the strength and hardenability of low carbon steel. Above 1.65% the steel tends to become air hardened, with resultant impairing of the ductility. Ni: Is beneficial to steel with less than about 0.40% C. Improving toughness at low temperatures and weldability Mo: Carbide former, it form complex carbides (FeMo) 6 C, Fe 21 Mo 2 C 6. Improved the yield strength, tensile strength and lowered DBTT of the steels V: Vanadium carbides make the material relatively resistant to thermal ageing, fine grained (tempered bainite) and strong but the weldability is not good (preheat treatment)

18 Material Chemical composition is a key issue for radiation embrittlement Strength increase with Ce=C+Si/24+Mn/6+Ni/40+Cr/5+Mo/4+V/14 C: Cementite improve hardness and strength of steel but decrease toughness properties. Should maintain to the minimum level needed to achieve the desired strength. Si: Silicon is used as deoxidizers. Improve the transition temperature Mn: Manganese is also use as deoxidizer, and improved the strength and hardenability of low carbon steel. Above 1.65% the steel tends to become air hardened, with resultant impairing of the ductility. Ni: Is beneficial to steel with less than about 0.40% C. Improving toughness at low temperatures and weldability Mo: Carbide former, it form complex carbides (FeMo) 6 C, Fe 21 Mo 2 C 6. Improved the yield strength, tensile strength and lowered DBTT of the steels V: Vanadium carbides make the material relatively resistant to thermal ageing, fine grained (tempered bainite) and strong but the weldability is not good (preheat treatment) Irradiation damage

19 Material RPV steel Impurities Cu: BM: In older plants come form the automotive (wiring) scrap used in the production of ingots W: Copper-coated electrodes: To minimize the oxidation of the wires during storage and improve electrical conductivity P, S: Impurity from the scrap Al, Sn, N, As, Co PWHT of welds: The amount of Cu in solid solution is less than bulk Cu. Cu already precipitate during PWHT. Increase of Ni at matrix and GB was also observed as a result of PWHT

20 Material RPV steel Impurities Cu: BM: In older plants come form the automotive (wiring) scrap used in the production of ingots W: Copper-coated electrodes: To minimize the oxidation of the wires during storage and improve electrical conductivity P, S: Impurity form the scrap Al, Sn, N, As, Co PWHT of welds: The amount of Cu in solid solution is less than bulk Cu. Cu already precipitate during PWHT. Increase of Ni at matrix and GB was also observed as a result of PWHT Irradiation damage

21 Material Trend of decrease of important impurities in RPV steels M. Brumovsky SOTERIA

22 Material The range of different alloying and impurities for plates and forgings Cu is higher for welds High-Ni welds and VVER base materials Similar Mn content P very high variability

23 20 15 Ni VVER 440 BM Ni USA A508C3 Ni USA A508C2 Ni French BM Material Ni USA A302B Ni USA A302BMod Ni USA A533B Ni Forging Ni Plates 0 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2, ,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2, Ni USA W L80 Plate Ni USA W L0091 Plate Ni USA W L1092 Plate Ni USA W L Ni USA W L80 Forging Ni USA W LW320 Forgings Ni VVER 440 W Ni VVER 1000 W Ni Weld (Forging) 10 5 Ni Welds (Plates) 0 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 0 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0

24 Mn USA A508C2 Mn USA A508C3 Mn French BM Mn VVER 440 BM Mn Forgings Material Mn USA A302B Mn USA A302BMod Mn USA A533B1 5 5 Mn Plates 0 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 0 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 9 6 Mn USA W L80 Forging Mn USA W LW320 Forgings Mn VVER 440 W Mn VVER 1000 W Mn Weld (Forging) 9 6 Mn USA W L80 Plate Mn USA W L0091 Plate Mn USA W L1092 Plate Mn USA W L124 Mn Welds (Plates) ,5 1,0 1,5 2,0 0 1,2 1,6 2,0

25 10 Si USA A508C2 Si USA A508C3 Si French BM Si VVER 440 BM 5 Si Forging Material Si USA A302B Si USA A302BMod Si USA A533B1 Si Plates 0 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0, ,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0, Si USA W L80 Forging Si USA LW320 Forgings Si French W Si VVER 440 W Si VVER 1000 W Si Weld (Forging) Si USA W L80 Plate Si USA L0091 Plate Si USA L1092 Plate Si USA W L124 Si Welds (Plates) ,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0, ,0 0,2 0,4 0,6 0,8

26 Material Cu USA A508C2 Cu USA A508C3 Cu French BM Cu VVER 440 BM Cu USA A302B Cu USA A302BMod Cu USA A533B1 Cu Forging Cu Plates 0,00 0,05 0,10 0,15 0,20 0,25 0,30 0,35 0,40 0,45 Cu USA W L80 Forging Cu USA W LW320 Forgings Cu VVER 440 W Cu VVER 1000 W Cu French W Cu Weld (Forging) 0,00 0,05 0,10 0,15 0,20 0,25 0,30 0,35 0,40 0,45 Cu USA W L80 Plate Cu USA W L0091 Plate Cu USA W L1092 Plate Cu USA W L124 Cu Welds (Plates) 0,00 0,05 0,10 0,15 0,20 0,25 0,30 0,35 0,40 0,45 0,00 0,05 0,10 0,15 0,20 0,25 0,30 0,35 0,40 0,45

27 15 10 P USA A508C2 P USA A508C3 P French BM P VVER 440 BM Material P USA A302B P USA A302BMod P USA A533B1 5 P Forging 5 P Plates 0 0,00 0,01 0,02 0,03 0,04 0 0,00 0,01 0,02 0,03 0,04 21 P USA W L80 Forging P USA LW320 Forgings P French W P VVER 440 W P VVER 1000 W 9 P USA W L80 Plate P USA L0091 Plate P USA L1092 Plate P USA W L P Welds (Plates) 7 P Weld (Forging) 3 0 0,00 0,01 0,02 0,03 0,04 0 0,01 0,02 0,03 0,04

28 FABRICATION

29 Fabrication Large vessels are fabricated by two methods. In the first method, rolled and welded plates are used to form separate steel courses. Such a vessel has both longitudinal and circumferential weld seams

30 Plates R.K. Nanstad

31 Plates R.K. Nanstad

32 Plates R.K. Nanstad

33 Fabrication In the second method, large ring forgings are used This method improves component reliability because of the lack of longitudinal welds. Weld seams are located to avoid intersection with nozzle penetration weldments.

34 Fabrication New RPV are made using forgings

35 Forgings M. Brumovsky

36 Forgings M. Brumovsky

37 Forgings M. Brumovsky

38 Fabrication Conventional submerged arc welding (SAW) of V and U-groove welds (edge angles up to 10 deg) has proven itself over the years and was the most frequently used welding procedure for thick walled nuclear primary components SAW involves formation of an arc between a continuously-fed bare wire electrode and the workpiece. The process uses a flux to generate protective gases and slag, and to add alloying elements to the weld pool

39 Fabrication Cladding over the major part of the vessel inner surface is applied by automatic submerged arc-welding (SAW) with strip electrodes of different sizes, normally 60 mm width. Local areas, for instance the inner radius of the main coolant nozzles, are cladded using a manual arc-welding process. Two layer strip cladding may also be used to eliminate underclad cracking and to reduce the susceptibility of the clad surface to intergranular stress corrosion cracking. Wire cladding is also used, notably in the USA Preheating is used for all layers of cladding and maintained throughout the process until post-weld heat-treatment is carried out, in order to avoid the possibility of cold cracking beneath the cladding.

40 Fabrication Post weld heat treatment PWHT stress relieving process whereby residual stresses are reduced in the welds, including the weld metal and Heat Affected Zone (HAZ) J.S. Lee KAERI

41 Fabrication Large forgings are used to reduce the number of welds and increase thickness But some micro and macro-segregation can take place in large ingots French Plant A Surveillance Doel and Tihange indications

42 Forgings Ingot solidification - The metal that solidifies first contains few alloying elements and these are released at the solidification front producing element enrichment in the still liquid metal and consequently element macro segregation after solidification. Moreover the segregated molten metal is less dense than the non-segregated molten metal and this leads to an upward movement along the solidification front In the case of hollow parts as core shells are, the elimination of the axial zone of the ingot during forging removes the major part of the macrosegregation S. SAILLET Fontevraud 6

43 Forgings EDF-AREVA large forgings project Surveillance results of a French NPP shoe atypical results not related to irradiation Metallurgical heterogeneities S. SAILLET Fontevraud 6

44 Macro-segregation Acceptance test and irradiation surveillance program coupons are taken from the end corresponding to the bottom of the initial ingot Zones affected by positive segregation can locally be present at the internal skin of the core shells The quarter-thickness of the acceptance ring, where the PVSP specimens come from with zero or negative segregation. Forgings S. SAILLET Fontevraud 6

45 Forgings During the outage of the Doel 3 nuclear power plant in June 2012, an in-service inspection revealed the existence of numerous quasilaminar indications in the reactor pressure vessel base metal. Comparable, yet fewer, indications were found three months later in the Tihange 2 nuclear power plant after a similar inspection All of the indications identified in Doel 3 and Tihange 2 are of a size, shape and nature that they would have been acceptable according to the ASME Code, Section III All of the indications in Doel 3 and Tihange 2 are structurally insignificant International Expert Review Board The indications found in the RPVs of Doel 3 and Tihange 2 were identified as being, most likely, hydrogen flakes that were created during manufacture and can be attributed to macro-segregations in the reactor vessel steels. The indications have not grown significantly in the 30 years the plants were in operation and will not grow significantly in the future under normal operating conditions.

46 Forgings 30/01/2013 (FANC) Doel 3 and Tihange 2 reactor pressure vessels: Provisional evaluation report 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 (333 sections). The location of the indications can be attributed to the existence of macro-segregations, which are typical of forgings made from large ingots. There are identified as hydrogen flakes

47 Forgings FANC Web Page 22 August 2014: << Doel 3 and Tihange 2 reactor vessels. Both reactors are in a shutdown state until further notice and the second accelerated irradiation test program conducted by Electrabel with the cooperation of SCK CEN is still in progress. In this respect, it is not possible so far to make any conclusion on the future of both reactors.>>

48 Summary RPV material used is low alloy steel High toughness low cost Ductile to brittle tansition Chemical composition affects neutron radiation sensitivity, especially welds Forging reduce the number of weld but can show defects