1 FIP/1-6Rb Manufacturing Design and Progress of the First Sector - PDF document

1 FIP/1-6Rb Manufacturing Design and Progress of the First Sector for ITER Vacuum Vessel H. J. Ahn 1 , G. H. Kim 1 , K. H. Hong 1 , H. S. Kim 1 , C. K. Park 1 , S. W. Jin 1 , H. G. Lee 1 , K. J. Jung 1 , J. S. Lee 2 , T. S. Kim 2 , T. H. Kwon 2 , B. R. Roh 2 , J. W. Sa 3 , Y. Utin 3 , C. Jun 3 , and C. H. Choi 3 1 National Fusion Research Institute, Daejeon, 305-333, Korea 2 Hyundai Heavy Industries Co. Ltd., Ulsan, 682-792, Korea 3 ITER Organization, Route de Vinon-sur-Verdon, CS 90 046, 13067 St. Paul Lez Durance Cedex, France E-mail contact of main author: hjahn@nfri.re.kr Abstract . The ITER vacuum vessel (VV) is a double walled torus structure and one of the most critical components in the fusion reactor. The design and fabrication of the VV as nuclear equipment shall be complied with the RCC-MR code and regulations of nuclear pressure equipment in France (ESPN). The manufacturing design of the first sector has been developed in accordance with the code and the demanding tolerance and inspection requirements by HHI as a supplier. The design of Korean sectors introduces two special design concepts to minimize welding distortion which are a self-sustaining welded IWS rib and cup-and-cone type segment joints. Reduced weld joints will mitigate the risk of sector tolerance mismatch. Several real scale mock- ups have been constructed to verify and develop the manufacturing design and procedures. Qualifications for welding, forming and NDE have been conducted before work start. The fabrication of the first sector was started in early 2012. All poloidal segments for the first sector are being fabricated simultaneously in Korea. The first sector has been manufacturing slowly at the front of ITER project as a nuclear component under strict regulations. Fabrication speed could be getting better after solving current issues. 1. Introduction The ITER Vacuum Vessel (VV) is a torus shaped double wall structure and consists of nine sectors and several ports. Main functions of the VV are to provide high vacuum for plasma operation and to protect radioactive contamination as the first safety barrier. The main material is austenitic stainless steel with controlled nitrogen contents and tight limitation of impurities such as cobalt, niobium and boron [1]. The ITER VV procurement sharing includes the production of 7 sectors by the EU, 2 sectors by the Republic of Korea (KO), the upper ports by the Russian Federation, the VV supports and the lower and equatorial ports by KO, the in-wall shielding (IWS) by the Republic of India and the assembly by the ITER Organization (IO). Korea Domestic Agency (KODA) contracted with Hyundai Heavy Industries Co., LTD (HHI) to product the VV sectors and major ports including the first sector which will be delivered before others. The design and fabrication of the VV as nuclear equipment shall be complied with the RCC- MR code and regulations of nuclear pressure equipment in France (ESPN). The manufacturing design has been developed to fabricate the main vessel and port structures in

2 FIP/1-6Rb accordance with the design requirements. All manufacturing sequences including welding methods are also established to meet the demanding tolerance and inspection requirements. 2. Detail Design of Vacuum Vessel The ITER VV is a double walled torus structure and consists of nine 40 degree vessel sectors with many port structures like long nozzles of a pressure vessel as shown in FIG. 1. The VV is a heavy welded structure with 60 mm thick shells, 40 mm ribs and flexible support housings of 275 mm diameter. Its weight is about 5250 tons and its torus outer diameter and height are 19.4 m and 11.4 m, respectively. The interspace between the vacuum vessel double walls is filled with IWS and cooling water. The shielding structures, which occupy about 60% of the in-wall space, provide efficient neutron shielding. FIG. 1. Configuration of the ITER Vacuum Vessel. 2.1. Classification and Applied Codes The VV provides high quality vacuum for plasma and primary radioactivity confinement boundary. The VV is classified into a safety important class (SIC) component based on the French safety and quality order 1984. This safety classification has been maintained in ITER as a sub-ensemble of Protection Important Components (PIC), in agreement with the requirements of the Order 7th February 2012. The VV design shall take into account the various loads combinations for which the VV safety functions are needed including seismic events [1]. The VV consists of an assembly of a number of individual nuclear pressure equipment (NPE) as per definition of the NPE Order 2005 [2]. The assembly will appear only after welding of the components supplied to the ITER site. The VV and some port sections are multi-chamber equipment. According to regulatory requirement, NPE Order, the VV are classified into category IV and nuclear level N2. The RCC-MR Code, Edition 2007, is selected as the design and construction code for mechanical components of nuclear installations. For items which are not covered by the Code, ITER Organization’s technical specifications are used. The VV and ports are classified as Class 2 box structure components and applicable design rules are provided in the RCC-MR RC 3800 chapter and complemented by Appendix 19 [3].

3 FIP/1-6Rb 2.2. Sector Design The VV is to be fabricated in the factory as nine sectors each spanning 40 degree. The weight of each sector is about 200 tons and its height and width are 13 m and 6 m, respectively. 60 mm-thick stainless steel plates forms a double-wall that contains additional 250 tons of IWS. A 40 degree sector consists of four poloidal segments which are inboard segment (PS1), upper segment (PS2), equatorial segment (PS3) and lower segment (PS4) as shown in FIG. 2. FIG. 2. Composition of a VV Sector. The baseline fabrication scheme of a VV sector is the welding of four poloidal segments with segment splices. The segment has inner and outer shells, T-shape poloidal ribs, flexible support housings (FSH), in-vessel coil (IVC) supports and port stub. The lower segment has special attachments such as gussets, pipe penetrations, triangular supports and divertor rails. 3. Manufacturing Design of Vacuum Vessel The manufacturing design of Korean sectors has two special design concepts to minimize welding distortion. One is a self-sustaining welded IWS support rib. The other is cup-and- cone type segment joints to reduce the butt welding work of poloidal ribs. Reduced weld joints will release the risk of sector tolerance mismatch. 3.1. Welding Design The shapes of the VV and ports are very complicated double structure and require severe dimension control. Based on these considerations, narrow gap gas tungsten arc welding (GTAW) and electron beam welding (EBW) procedures were considered as the main welding process. GTAW processes are divided into a manual type and a machine type in terms of their accessibility and productivity. HHI has developed three different types of welding equipment which are to be applied in main shell butt welding, rib to shell welding and shell to FSH with narrow gap joint and hot wire system [4]. T-shape adapters are introduced to the welding joints between outer shell and rib, which satisfies the code requirements such as the full penetration weld and the minimum distance between the welds due to lots weld components and complexity of assembly. For EBW

4 FIP/1-6Rb between inner shell and FSHs of inboard segment, tight fit-up with gap less than 0.1 mm is required to achieve required welding quality. The details of major welding joint for inboard segment are demonstrated in FIG. 3. Butt welding between inner shells adopts double U-type groove joint and be examined by radiographic testing (RT) because of both side accessibility. Outer shell welding should require narrow U-type groove and ultrasonic testing (UT) because of lack of back side accessibility. FIG. 3. Welding Joint Details for inboard Segment: (a) inner shell to inner shell, (c) FSHs and Ribs to outer shell (c) Ribs on inner shell. In case of welds to be examined by ultrasonic test (UT), the minimum distance between the welds is the larger 1.5 times the thickness of the thickest part to be assembled or 40 mm. These welding designs comply with the code requirements such as the full penetration weld and the minimum distance between the welds as well as 100% volumetric NDE condition. To minimize welding deformation of FSHs which have very tight tolerance for blanket assembly, a self-sustaining weld concept is applied to IWS support ribs. The self-sustaining welded rib has discrete welded parts and just contact parts between the IWS support rib and FSHs as shown in FIG. 4. The contact zone takes a role as a stopper to restrain the welding contraction. FIG. 4. Self-sustaining Welded IWS Support Rib 3.2. Fabrication Sequence of a Segment The manufacturing sequence of segments has been developed based on the welding distortion analyses wi th HHI’s wide experiences to satisfy the design requirement. EBW and narrow gap TIG welding techniques are adopted and developed through the manufacturing mock-ups.