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Progress of the ITER Thermal Shields
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Progress of the ITER Thermal Shields Namil Her a,∗ , Robby Hick III a , Robin Le Barbier a , Terenig Arzoumanian a , Chang-Ho Choi a , Carlo Sborchia a , Wooho Chung b , Kwanwoo Nam b , Chang Hyun Noh b , Dong Kwon Kang b , Gyoung-O. Kang b , Youngkil Kang c , Kisuk Lim c a b c
ITER Organisation, Route de Vinon-sur-Verdon – CS 90046, 13067 St Paul-lez-Durance Cedex, France ITER Korea, National Fusion Research Institute, Daejeon 34133, Republic of Korea SFA Engineering Corporation, Hwaseong-si, Gyeonggi-do 10060, Republic of Korea
h i g h l i g h t s • • • •
Design improvement of the ITER Thermal Shields was introduced. Design of TS manifold and TS instrumentation were summarized. Produced main material of the TS (SS304LN) was summarized. Status of the VVTS manufacturing and the inspection requirements were summarized.
a r t i c l e
i n f o
Article history: Received 28 August 2015 Received in revised form 21 January 2016 Accepted 22 January 2016 Available online xxx Keywords: ITER Thermal Shields Design Manufacturing Tolerance Silver Electroplating
a b s t r a c t The role of the ITER Thermal Shields (TS) is to minimize the radiation heat load from the warm components such as vacuum vessel and cryostat to magnet operating at 4.5 K. The final design of TS was completed in 2013 and manufacturing of the vacuum vessel thermal shield (VVTS) is now on-going. This paper describes the development status of the TS in particular the design improvements, the fabrication and the requirements. © 2016 Elsevier B.V. All rights reserved.
1. Introduction The ITER machine is an international effort aimed at demonstrating the scientific and technological feasibility of fusion energy. ITER is specified as a Nuclear Facility INB-174. ITER Thermal Shields (TS) is not a Protection Important Components (PIC). TS is located between the vacuum vessel/the cryostat and the magnet in order to protect the magnet from excessive thermal radiation transferring from warm surfaces. The TS consists of Vacuum Vessel Thermal Shield (VVTS), Cryostat Thermal Shield (CTS) as shown in. Fig. 1. The TS is actively cooled by helium gas which flows inside the cooling tubes welded on the TS surface. Supply temperature and operating pressure are 80 K and 1.8 MPa, respectively. Cooling tube should be effectively routed on the TS so as to
∗ Corresponding author. E-mail address: [email protected] (N. Her).
minimize local excessive temperature rise and the resulting heat load to the magnet that operates at 4.5 K [1,2]. Purpose of the TS is to provide a thermal shield from the hot components of the tokamak (mainly the VV and cryostat and associated water manifolds) to the cold components of the superconducting magnets [3]. It is composed of a torus and port shaped shield as well as a cylindrical shaped shield with associated openings for penetrations. It is a single wall structure primarily fabricated with stainless steel 304LN. Pressurized helium gas flows from the cold valve box located outside the cryostat boundary and through 8 parallel isolation valves into the TS manifolds (TSM) located inside the cryostat. From the TSM the helium is distributed into seamless and continuous cooling tubes that are stagger welded to the TS panels. During normal plasma operating conditions, the power from the TS to the surfaces at 4.5 K is limited to 2.2 kW. This load is derived from radiation through cryostat vacuum and conduction through the TS supports. In addition to the total power load, the maximum
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Fig. 3. Temporary support design concept for UCTS cylinder assembly.
Fig. 1. ITER TS system.
Fig. 4. TS manifold.
Fig. 2. Pre-assembled UCTS cylinder.
surface heat flux on the 4.5 K surfaces is limited to 40 W/m2 locally, whilst always ensuring that the above total load (2.2 kW) is not exceeded. Thermal radiation to the superconducting magnets is minimized by providing surfaces with low emissivity [4]. High vacuum in the cryostat chamber minimizes free molecular gas convection. Heat conduction occurs through the TS rigid support structures. To minimize the heat conduction through the supports, their number and design have been optimized whilst maintaining the structural integrity of the TS. The design of ITER thermal shield has been carried out by ITER Korea in cooperation with ITER organization. This paper describes the development status of the TS in particular the design improvements, the manufacturing and the requirements.
2. TS design improvement 2.1. UCTS design The UCTS (upper cryostat thermal shield) consists of the upper CTS lid and the upper CTS cylinder, and it is supported from mounts off the cryostat lid. Since completion of the final design of the TS components in 2012, the design of UCTS assembly tool has been improved to simplify the assembly operation in the pit. The tool attachment on the UCTS cylinder shall be modified in accordance with the improved tool design. As shown in Fig. 2, pre-assembled UCTS cylinder in the assembly hall will be supported temporarily on the VV upper ports in the pit. This improved assembly scheme can reduce the handling risk when the huge temporary support of the previous design is removed after the installation. Fig. 3 shows the design concept of temporary support and the attachment on the UCTS cylinder. Feasibility study on improved
Fig. 5. Improved design of the connecting pipe for UCTS (left) and ECTS (right).
design has been performed. Structural rib will be added on the UCTS panel to prevent stress concentration when seismic load is applied. 2.2. TSM design For the cooling of the TS panels, total 8 TSMs are located inside of the cryostat and connected to the cry-distribution system installed outside of the cryostat. During the final design review of the TS, TSM design improvement was requested to simplify the interfaces and increase the structural integrity. Redundant manifold rings located between the cryostat and TS remain near room temperature during machine cool-down. To accommodate the radial shrinkage of the TS panel a large toroidal displacement is induced on the rings. Flexibility in the connecting pipes between the ring and panel is necessary and this reduces the available space in the cryostat for the assembly and the maintenance. TSM rings and feeders were removed and Figs. 4 show the improved design of the connecting pipe for UCTS and Equatorial CTS (ECTS). Redundancy cooling tubes attached on the TS panel and the connecting pipes are extended to accessible area for the switching of the circuits. The improved design gives us (a) increase space for in-cryostat access; (b) reduce stress on manifold and connecting pipes; (c)
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Table 1 TS instrumentations. Instrument
Sensor type
Location
Quantity
Temperature
Platinum resistance Strain gauge Draw-wire
VVTS CTS VVTS support UCTS, ECTS
100 127 45 20
Strain Displacement
Table 2 Material properties of the stainless steel 304LN. Material properties
Requirement
Yield strength (MPa) Elongation (%) Fracture toughness (J) Fracture toughness (J) Magnetic permeability
270 min. 40 min. 100 min. 60 min. 1.05 max.
Measured values
Fig. 6. Equivalent stress of TSM #2 under load Cat. III. 300–340 55–60 260–320 140–210 1.01–1.02
Test temperature (◦ C) 20 20 20 −196 20
the VVTS supports and full bridge configuration is applied to the measurement. Displacement sensors will provide data of the displacements and deformations of the UCTS and ECTS. A total of 20 displacement sensors (draw-wire type) are proposed. 3. TS materials Fig. 7. Equivalent stress distribution of the crown support under the load Cat. IV.
simplify the cryo-distribution system; (d) reduce assembly burden; (e) reduce number of welds of the TSM pipes; (f) increase TS reliability. Even though tokamak operating experience shows that after the commissioning period, stainless steel cryogenic pipe transport systems are extremely reliable and the probability of a leak requiring repair after commissioning is extremely unlikely, dedicated efforts on the TSM test and inspection during the manufacturing and the installation are required. Equivalent stress on the pipe is checked in the active condition, which means helium flow through the pipe. High stress on the pipe is located mainly on the elbow or TEE joint. As shown in Fig. 6, the stress level on the TSM#2 is similar with TSM#1 due to the similar shape of TSM feeder. Maximum stress under load Cat. III is 94 MPa which is less than allowable level. Stress margin is 193% [5]. Fig. 7 shows the structural analysis was performed for the severe load case which is load Cat. IV. Reaction forces from the pipe analysis are applied on the support detailed model. Maximum stress of the support is 235 MPa on the outlet feeder support which are attached to the cryostat. Margin to allowable is 45%. Other supports have much margin comparing with feeder support. 2.3. TSI design The TS instrumentation (TSI) consists of transducers (temperature, strain and displacement), cables and connectors that transmit the signal to the control cubicles outside the tokamak, feed-through for crossing the cryostat vacuum boundary and data acquisition systems that process the signal to guarantee its accessibility by the CODAC. Table 1 shows the TS instrumentations. The primary function of temperature measurements is to map the structures’ general behavior. The sensors are spread on every TS structure and allow for comparisons to be made between TS components. Platinum resistance sensor (PT-103) will be attached on 227 temperature measurement points. Strain gauges are distributed on the VVTS support structures, inboard strips and outboard support rods. A total 45 strain gauges are used for characterization monitoring of
Main material of the TS is stainless steel 304LN for the frame and panel. Stainless steel TP304L will be used for the cooling pipe and manifold. For the support structures and bolts/nuts high strength steel (stainless steel 316LN) and alloy (Alloy 718 and Ti-6Al-4V) will be used. G10 is insulation material of the TS. About 1500 tons of stainless steel 304LN (EN grade X2CrNiN 1810 (steel number 1.4311)) plates have been produced by Industeel France and shipped to the TS manufacturing factory. Co (Cobalt) and Nb (Niobium) contents of the stainless steel 304LN are limited to below 0.1. All plates met the requirements and the range of the measured Co and Nb contents were 0.00–0.01 and 0.02–0.04, respectively. Table 2 shows the material properties of the produced material. The measured mechanical properties met the requirements. Charpy method was applied on the fracture toughness test. Measurement range of the magnetic permeability was 1.01–1.02 [6]. 4. VVTS manufacturing 4.1. Manufacturing procedures The inboard part of the VVTS is made of one 20 mm thick plate with continuously welded flanges. The inboard is divided into upper and lower parts at the bisection joint. A single cooling loop is attached on the 20◦ and 10◦ half sectors, respectively. The outboard shield is also made up of one 20 mm thick plate with continuously welded flanges to the edges of the panels. The outboard shield is also divided into upper and lower parts at the bisection joint. A single cooling loop is attached on each 10◦ half sector. Manufacturing of the VVTS 40◦ sector #5 and #6 have been started at the end of 2014. The manufacturing processes are primary buffing, cutting, welding & NDE, machining, VVTS 40◦ sector pre-assembly, pressure and leak testing, silver electroplating and packing. The manufacturing sequences details are described in the manufacturing and inspection plan (MIP) and the related procedures are linked with the MIP. VVTS 10◦ prototype was manufactured to confirm the manufacturing procedures, especially for the forming and bending of the shell, shell to flange welding and NDE (Non Destructive
Please cite this article in press as: N. Her, et al., Progress of the ITER Thermal Shields, Fusion Eng. Des. (2016), http://dx.doi.org/10.1016/j.fusengdes.2016.01.050
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Table 3 Manufacturing tolerances of the VVTS. VVTS tolerance items
Tolerance (mm)
Overall vertical Overall radial Surface deviation on outboard Surface deviation on inboard Surface deviation on port shroud Bolt hole on the flange Overall toroidal for 40◦ sector Overall toroidal for 20◦ sector Overall toroidal for 10◦ sector In-pit joint vertical and radial
± 20 ±5 ± 15 ± 10 ±6 ±2 ±5 ±3 ±2 ±7
Fig. 8. VVTS 10◦ prototype manufacturing.
Examination), cooling tube bending and welding on the shell and the pre-assembly. Fig. 8 shows the manufactured prototype. Most of manufacturing procedures have been confirmed by the prototype except for the sequences on the flange and shell welding. Improved welding sequence is applied on the manufacturing of the VVTS. Fig. 9 shows manufacturing sequence of the VVTS 40◦ sector. 4.2. Test and inspection VVTS will be installed between VV and TFC and the gaps (VVTS/VV and VVTS/TFC) are narrow compared with the dimensions of those components. Very tight dimensional control is required during the manufacturing and the installation to avoid clashes. Manufacturing tolerances of the VVTS have been developed at the beginning of the project and the same requirements have been applied to the manufacturing. Required manufacturing tolerance of the VVTS 40◦ sector are summarized in Table 3. The factory pre-assembly of VVTS 40◦ sector is an important procedure of the inspection process. It is required high accuracy of alignment with the templates. In order to achieve the degree of precision required at this critical assembly stage, the use of an advanced global surveying technique, such as 3D scanner will be used.
Fig. 10. Jig design for the pre-assembly of the VVTS.
Accurate marking of the section position relative to the templates and the in-pit joint halves relative to the flange is necessary before disassembly of the sector and detachment of the in-pit joint halves. This step will require a close collaboration with the IO assembly group. Fig. 10 shows the jig model for the pre-assembly of VVTS 40◦ sector in the factory. One 40◦ inboard and two 20◦ outboards will be pre-assembled then port shrouds will be integrated. Fixing conditions of the pre-assembly will be the same as the VVTS and VV temporary supports conditions in the IO assembly hall.
Fig. 9. VVTS 40◦ sector manufacturing sequence.
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Fig. 11. Schematic diagram of helium leak testing.
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at room temperature. Dedicated R&D on the silver electroplating has been performed by the manufacturer to develop the procedure. After silver electroplating the addition of a passivation process will be performed to prevent discoloration and to improve the reliability of the coating surface. Fig. 12 shows the constructed electroplating facility. It has total 11 baths and each baths has 9 m length, 3 m width and 6 m height. The construction will be completed by end of 2015 then the process will be qualified using the qualification mock-up. Pressure test, vacuum leak test and insulation resistance test will be performed after silver coating. The test method and conditions are the same as those of the test before silver coating. Test should be done at the isolated area that is free of dust, scale or foreign materials which would adversely affect the quality of the silver coated surface. The insulation resistance test will be done for the Inboard 40◦ sector and the outboard 20◦ sector. After checking all surfaces free of dirt, oil, contamination or damage, ambient temperature and humidity are recorded before Megger test. 5. Conclusion This paper describes the development status of the TS in particular the design improvement, the manufacturing and the requirements. Most of the major issues on the TS design have been solved except for the new assembly interface issues. The remaining issues shall be solved soon. Important technical aspects and requirements on the VVTS manufacturing such as the manufacturing tolerances, leak tightness of the cooling tubes and the quality of the silver electroplating were summarized. Since the start of the manufacturing of the VVTS sector #5 and #6 in October 2014 and major manufacturing activities such as welding and NDE are ongoing now. Acknowledgments
Fig. 12. Constructed silver electroplating facility.
The pressure test will be performed with nitrogen gas under room temperature. The vacuum leak testing will be conducted after the pressure proof test. The test will be made at room temperature for all TS main components. If there are any pipe to pipe joints on the inaccessible components (VVTS ports and port shrouds), they will be subjected to a cold shock procedure close to 80 K before being tested at room temperature. The vacuum leak test will be made with pressure differential in the same direction as for operation of the TS components. The TS component is inserted into a vacuum chamber and the cooling tube is charged with helium gas (3.0 MPa). Maximum allowable leak rate is 1 × 10−9 Pa m3 s−1 . Fig. 11 shows the schematic diagram of the helium leak testing. Silver electroplating is one of the important manufacturing processes for the TS and requires process qualification. Required emissivity on the TS surface after silver electroplating is below 0.05
The authors acknowledge the support of members of ITER IO, ITER-Korea for the various activities reported in this paper. ITER Disclaimer: The views and opinions expressed herein do not necessarily reflect those of the ITER Organization. References [1] V. Bykov, et al., The thermal shields for the ITER magnet system: thermal, structural and assembly aspects, Fusion Eng. Des. 58–59 (2001) 177–182. [2] C.H. Noh, et al., Final design of ITER vacuum vessel thermal shield, Fusion Eng. Des. 88 (2013) 1896–1899. [3] C.H. Noh, et al., Final Design of ITER Thermal Shield Manifold, Fusion Engineering and Design. In Progress, 2015. [4] K. Nam, W. Chung, C.H. Noh, et al., Thermal analysis on detailed 3D models of ITER thermal shield, Fusion Eng. Des. 89 (2014) 1843–1847. [5] C.H. Noh, et al., Piping structural design for the ITER thermal shield manifolds, Fusion Eng. Des. 98–99 (2015) 1453–1456. [6] Summary of material data for structural analysis of the thermal shield, ITER DA4PYQ, private communication, 2012.
Please cite this article in press as: N. Her, et al., Progress of the ITER Thermal Shields, Fusion Eng. Des. (2016), http://dx.doi.org/10.1016/j.fusengdes.2016.01.050
ARTICLE IN PRESS
FUSION-8490; No. of Pages 5
Fusion Engineering and Design xxx (2016) xxx–xxx
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Progress of the ITER Thermal Shields Namil Her a,∗ , Robby Hick III a , Robin Le Barbier a , Terenig Arzoumanian a , Chang-Ho Choi a , Carlo Sborchia a , Wooho Chung b , Kwanwoo Nam b , Chang Hyun Noh b , Dong Kwon Kang b , Gyoung-O. Kang b , Youngkil Kang c , Kisuk Lim c a b c
ITER Organisation, Route de Vinon-sur-Verdon – CS 90046, 13067 St Paul-lez-Durance Cedex, France ITER Korea, National Fusion Research Institute, Daejeon 34133, Republic of Korea SFA Engineering Corporation, Hwaseong-si, Gyeonggi-do 10060, Republic of Korea
h i g h l i g h t s • • • •
Design improvement of the ITER Thermal Shields was introduced. Design of TS manifold and TS instrumentation were summarized. Produced main material of the TS (SS304LN) was summarized. Status of the VVTS manufacturing and the inspection requirements were summarized.
a r t i c l e
i n f o
Article history: Received 28 August 2015 Received in revised form 21 January 2016 Accepted 22 January 2016 Available online xxx Keywords: ITER Thermal Shields Design Manufacturing Tolerance Silver Electroplating
a b s t r a c t The role of the ITER Thermal Shields (TS) is to minimize the radiation heat load from the warm components such as vacuum vessel and cryostat to magnet operating at 4.5 K. The final design of TS was completed in 2013 and manufacturing of the vacuum vessel thermal shield (VVTS) is now on-going. This paper describes the development status of the TS in particular the design improvements, the fabrication and the requirements. © 2016 Elsevier B.V. All rights reserved.
1. Introduction The ITER machine is an international effort aimed at demonstrating the scientific and technological feasibility of fusion energy. ITER is specified as a Nuclear Facility INB-174. ITER Thermal Shields (TS) is not a Protection Important Components (PIC). TS is located between the vacuum vessel/the cryostat and the magnet in order to protect the magnet from excessive thermal radiation transferring from warm surfaces. The TS consists of Vacuum Vessel Thermal Shield (VVTS), Cryostat Thermal Shield (CTS) as shown in. Fig. 1. The TS is actively cooled by helium gas which flows inside the cooling tubes welded on the TS surface. Supply temperature and operating pressure are 80 K and 1.8 MPa, respectively. Cooling tube should be effectively routed on the TS so as to
∗ Corresponding author. E-mail address: [email protected] (N. Her).
minimize local excessive temperature rise and the resulting heat load to the magnet that operates at 4.5 K [1,2]. Purpose of the TS is to provide a thermal shield from the hot components of the tokamak (mainly the VV and cryostat and associated water manifolds) to the cold components of the superconducting magnets [3]. It is composed of a torus and port shaped shield as well as a cylindrical shaped shield with associated openings for penetrations. It is a single wall structure primarily fabricated with stainless steel 304LN. Pressurized helium gas flows from the cold valve box located outside the cryostat boundary and through 8 parallel isolation valves into the TS manifolds (TSM) located inside the cryostat. From the TSM the helium is distributed into seamless and continuous cooling tubes that are stagger welded to the TS panels. During normal plasma operating conditions, the power from the TS to the surfaces at 4.5 K is limited to 2.2 kW. This load is derived from radiation through cryostat vacuum and conduction through the TS supports. In addition to the total power load, the maximum
http://dx.doi.org/10.1016/j.fusengdes.2016.01.050 0920-3796/© 2016 Elsevier B.V. All rights reserved.
Please cite this article in press as: N. Her, et al., Progress of the ITER Thermal Shields, Fusion Eng. Des. (2016), http://dx.doi.org/10.1016/j.fusengdes.2016.01.050
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Fig. 3. Temporary support design concept for UCTS cylinder assembly.
Fig. 1. ITER TS system.
Fig. 4. TS manifold.
Fig. 2. Pre-assembled UCTS cylinder.
surface heat flux on the 4.5 K surfaces is limited to 40 W/m2 locally, whilst always ensuring that the above total load (2.2 kW) is not exceeded. Thermal radiation to the superconducting magnets is minimized by providing surfaces with low emissivity [4]. High vacuum in the cryostat chamber minimizes free molecular gas convection. Heat conduction occurs through the TS rigid support structures. To minimize the heat conduction through the supports, their number and design have been optimized whilst maintaining the structural integrity of the TS. The design of ITER thermal shield has been carried out by ITER Korea in cooperation with ITER organization. This paper describes the development status of the TS in particular the design improvements, the manufacturing and the requirements.
2. TS design improvement 2.1. UCTS design The UCTS (upper cryostat thermal shield) consists of the upper CTS lid and the upper CTS cylinder, and it is supported from mounts off the cryostat lid. Since completion of the final design of the TS components in 2012, the design of UCTS assembly tool has been improved to simplify the assembly operation in the pit. The tool attachment on the UCTS cylinder shall be modified in accordance with the improved tool design. As shown in Fig. 2, pre-assembled UCTS cylinder in the assembly hall will be supported temporarily on the VV upper ports in the pit. This improved assembly scheme can reduce the handling risk when the huge temporary support of the previous design is removed after the installation. Fig. 3 shows the design concept of temporary support and the attachment on the UCTS cylinder. Feasibility study on improved
Fig. 5. Improved design of the connecting pipe for UCTS (left) and ECTS (right).
design has been performed. Structural rib will be added on the UCTS panel to prevent stress concentration when seismic load is applied. 2.2. TSM design For the cooling of the TS panels, total 8 TSMs are located inside of the cryostat and connected to the cry-distribution system installed outside of the cryostat. During the final design review of the TS, TSM design improvement was requested to simplify the interfaces and increase the structural integrity. Redundant manifold rings located between the cryostat and TS remain near room temperature during machine cool-down. To accommodate the radial shrinkage of the TS panel a large toroidal displacement is induced on the rings. Flexibility in the connecting pipes between the ring and panel is necessary and this reduces the available space in the cryostat for the assembly and the maintenance. TSM rings and feeders were removed and Figs. 4 show the improved design of the connecting pipe for UCTS and Equatorial CTS (ECTS). Redundancy cooling tubes attached on the TS panel and the connecting pipes are extended to accessible area for the switching of the circuits. The improved design gives us (a) increase space for in-cryostat access; (b) reduce stress on manifold and connecting pipes; (c)
Please cite this article in press as: N. Her, et al., Progress of the ITER Thermal Shields, Fusion Eng. Des. (2016), http://dx.doi.org/10.1016/j.fusengdes.2016.01.050
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Table 1 TS instrumentations. Instrument
Sensor type
Location
Quantity
Temperature
Platinum resistance Strain gauge Draw-wire
VVTS CTS VVTS support UCTS, ECTS
100 127 45 20
Strain Displacement
Table 2 Material properties of the stainless steel 304LN. Material properties
Requirement
Yield strength (MPa) Elongation (%) Fracture toughness (J) Fracture toughness (J) Magnetic permeability
270 min. 40 min. 100 min. 60 min. 1.05 max.
Measured values
Fig. 6. Equivalent stress of TSM #2 under load Cat. III. 300–340 55–60 260–320 140–210 1.01–1.02
Test temperature (◦ C) 20 20 20 −196 20
the VVTS supports and full bridge configuration is applied to the measurement. Displacement sensors will provide data of the displacements and deformations of the UCTS and ECTS. A total of 20 displacement sensors (draw-wire type) are proposed. 3. TS materials Fig. 7. Equivalent stress distribution of the crown support under the load Cat. IV.
simplify the cryo-distribution system; (d) reduce assembly burden; (e) reduce number of welds of the TSM pipes; (f) increase TS reliability. Even though tokamak operating experience shows that after the commissioning period, stainless steel cryogenic pipe transport systems are extremely reliable and the probability of a leak requiring repair after commissioning is extremely unlikely, dedicated efforts on the TSM test and inspection during the manufacturing and the installation are required. Equivalent stress on the pipe is checked in the active condition, which means helium flow through the pipe. High stress on the pipe is located mainly on the elbow or TEE joint. As shown in Fig. 6, the stress level on the TSM#2 is similar with TSM#1 due to the similar shape of TSM feeder. Maximum stress under load Cat. III is 94 MPa which is less than allowable level. Stress margin is 193% [5]. Fig. 7 shows the structural analysis was performed for the severe load case which is load Cat. IV. Reaction forces from the pipe analysis are applied on the support detailed model. Maximum stress of the support is 235 MPa on the outlet feeder support which are attached to the cryostat. Margin to allowable is 45%. Other supports have much margin comparing with feeder support. 2.3. TSI design The TS instrumentation (TSI) consists of transducers (temperature, strain and displacement), cables and connectors that transmit the signal to the control cubicles outside the tokamak, feed-through for crossing the cryostat vacuum boundary and data acquisition systems that process the signal to guarantee its accessibility by the CODAC. Table 1 shows the TS instrumentations. The primary function of temperature measurements is to map the structures’ general behavior. The sensors are spread on every TS structure and allow for comparisons to be made between TS components. Platinum resistance sensor (PT-103) will be attached on 227 temperature measurement points. Strain gauges are distributed on the VVTS support structures, inboard strips and outboard support rods. A total 45 strain gauges are used for characterization monitoring of
Main material of the TS is stainless steel 304LN for the frame and panel. Stainless steel TP304L will be used for the cooling pipe and manifold. For the support structures and bolts/nuts high strength steel (stainless steel 316LN) and alloy (Alloy 718 and Ti-6Al-4V) will be used. G10 is insulation material of the TS. About 1500 tons of stainless steel 304LN (EN grade X2CrNiN 1810 (steel number 1.4311)) plates have been produced by Industeel France and shipped to the TS manufacturing factory. Co (Cobalt) and Nb (Niobium) contents of the stainless steel 304LN are limited to below 0.1. All plates met the requirements and the range of the measured Co and Nb contents were 0.00–0.01 and 0.02–0.04, respectively. Table 2 shows the material properties of the produced material. The measured mechanical properties met the requirements. Charpy method was applied on the fracture toughness test. Measurement range of the magnetic permeability was 1.01–1.02 [6]. 4. VVTS manufacturing 4.1. Manufacturing procedures The inboard part of the VVTS is made of one 20 mm thick plate with continuously welded flanges. The inboard is divided into upper and lower parts at the bisection joint. A single cooling loop is attached on the 20◦ and 10◦ half sectors, respectively. The outboard shield is also made up of one 20 mm thick plate with continuously welded flanges to the edges of the panels. The outboard shield is also divided into upper and lower parts at the bisection joint. A single cooling loop is attached on each 10◦ half sector. Manufacturing of the VVTS 40◦ sector #5 and #6 have been started at the end of 2014. The manufacturing processes are primary buffing, cutting, welding & NDE, machining, VVTS 40◦ sector pre-assembly, pressure and leak testing, silver electroplating and packing. The manufacturing sequences details are described in the manufacturing and inspection plan (MIP) and the related procedures are linked with the MIP. VVTS 10◦ prototype was manufactured to confirm the manufacturing procedures, especially for the forming and bending of the shell, shell to flange welding and NDE (Non Destructive
Please cite this article in press as: N. Her, et al., Progress of the ITER Thermal Shields, Fusion Eng. Des. (2016), http://dx.doi.org/10.1016/j.fusengdes.2016.01.050
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Table 3 Manufacturing tolerances of the VVTS. VVTS tolerance items
Tolerance (mm)
Overall vertical Overall radial Surface deviation on outboard Surface deviation on inboard Surface deviation on port shroud Bolt hole on the flange Overall toroidal for 40◦ sector Overall toroidal for 20◦ sector Overall toroidal for 10◦ sector In-pit joint vertical and radial
± 20 ±5 ± 15 ± 10 ±6 ±2 ±5 ±3 ±2 ±7
Fig. 8. VVTS 10◦ prototype manufacturing.
Examination), cooling tube bending and welding on the shell and the pre-assembly. Fig. 8 shows the manufactured prototype. Most of manufacturing procedures have been confirmed by the prototype except for the sequences on the flange and shell welding. Improved welding sequence is applied on the manufacturing of the VVTS. Fig. 9 shows manufacturing sequence of the VVTS 40◦ sector. 4.2. Test and inspection VVTS will be installed between VV and TFC and the gaps (VVTS/VV and VVTS/TFC) are narrow compared with the dimensions of those components. Very tight dimensional control is required during the manufacturing and the installation to avoid clashes. Manufacturing tolerances of the VVTS have been developed at the beginning of the project and the same requirements have been applied to the manufacturing. Required manufacturing tolerance of the VVTS 40◦ sector are summarized in Table 3. The factory pre-assembly of VVTS 40◦ sector is an important procedure of the inspection process. It is required high accuracy of alignment with the templates. In order to achieve the degree of precision required at this critical assembly stage, the use of an advanced global surveying technique, such as 3D scanner will be used.
Fig. 10. Jig design for the pre-assembly of the VVTS.
Accurate marking of the section position relative to the templates and the in-pit joint halves relative to the flange is necessary before disassembly of the sector and detachment of the in-pit joint halves. This step will require a close collaboration with the IO assembly group. Fig. 10 shows the jig model for the pre-assembly of VVTS 40◦ sector in the factory. One 40◦ inboard and two 20◦ outboards will be pre-assembled then port shrouds will be integrated. Fixing conditions of the pre-assembly will be the same as the VVTS and VV temporary supports conditions in the IO assembly hall.
Fig. 9. VVTS 40◦ sector manufacturing sequence.
Please cite this article in press as: N. Her, et al., Progress of the ITER Thermal Shields, Fusion Eng. Des. (2016), http://dx.doi.org/10.1016/j.fusengdes.2016.01.050
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ARTICLE IN PRESS N. Her et al. / Fusion Engineering and Design xxx (2016) xxx–xxx
Fig. 11. Schematic diagram of helium leak testing.
5
at room temperature. Dedicated R&D on the silver electroplating has been performed by the manufacturer to develop the procedure. After silver electroplating the addition of a passivation process will be performed to prevent discoloration and to improve the reliability of the coating surface. Fig. 12 shows the constructed electroplating facility. It has total 11 baths and each baths has 9 m length, 3 m width and 6 m height. The construction will be completed by end of 2015 then the process will be qualified using the qualification mock-up. Pressure test, vacuum leak test and insulation resistance test will be performed after silver coating. The test method and conditions are the same as those of the test before silver coating. Test should be done at the isolated area that is free of dust, scale or foreign materials which would adversely affect the quality of the silver coated surface. The insulation resistance test will be done for the Inboard 40◦ sector and the outboard 20◦ sector. After checking all surfaces free of dirt, oil, contamination or damage, ambient temperature and humidity are recorded before Megger test. 5. Conclusion This paper describes the development status of the TS in particular the design improvement, the manufacturing and the requirements. Most of the major issues on the TS design have been solved except for the new assembly interface issues. The remaining issues shall be solved soon. Important technical aspects and requirements on the VVTS manufacturing such as the manufacturing tolerances, leak tightness of the cooling tubes and the quality of the silver electroplating were summarized. Since the start of the manufacturing of the VVTS sector #5 and #6 in October 2014 and major manufacturing activities such as welding and NDE are ongoing now. Acknowledgments
Fig. 12. Constructed silver electroplating facility.
The pressure test will be performed with nitrogen gas under room temperature. The vacuum leak testing will be conducted after the pressure proof test. The test will be made at room temperature for all TS main components. If there are any pipe to pipe joints on the inaccessible components (VVTS ports and port shrouds), they will be subjected to a cold shock procedure close to 80 K before being tested at room temperature. The vacuum leak test will be made with pressure differential in the same direction as for operation of the TS components. The TS component is inserted into a vacuum chamber and the cooling tube is charged with helium gas (3.0 MPa). Maximum allowable leak rate is 1 × 10−9 Pa m3 s−1 . Fig. 11 shows the schematic diagram of the helium leak testing. Silver electroplating is one of the important manufacturing processes for the TS and requires process qualification. Required emissivity on the TS surface after silver electroplating is below 0.05
The authors acknowledge the support of members of ITER IO, ITER-Korea for the various activities reported in this paper. ITER Disclaimer: The views and opinions expressed herein do not necessarily reflect those of the ITER Organization. References [1] V. Bykov, et al., The thermal shields for the ITER magnet system: thermal, structural and assembly aspects, Fusion Eng. Des. 58–59 (2001) 177–182. [2] C.H. Noh, et al., Final design of ITER vacuum vessel thermal shield, Fusion Eng. Des. 88 (2013) 1896–1899. [3] C.H. Noh, et al., Final Design of ITER Thermal Shield Manifold, Fusion Engineering and Design. In Progress, 2015. [4] K. Nam, W. Chung, C.H. Noh, et al., Thermal analysis on detailed 3D models of ITER thermal shield, Fusion Eng. Des. 89 (2014) 1843–1847. [5] C.H. Noh, et al., Piping structural design for the ITER thermal shield manifolds, Fusion Eng. Des. 98–99 (2015) 1453–1456. [6] Summary of material data for structural analysis of the thermal shield, ITER DA4PYQ, private communication, 2012.
Please cite this article in press as: N. Her, et al., Progress of the ITER Thermal Shields, Fusion Eng. Des. (2016), http://dx.doi.org/10.1016/j.fusengdes.2016.01.050