Vacuum Vessel Thermal Shield Research Articles

Fabrication and load test of ITER assembly tools for lifting heavy components

Korea Domestic Agency (ITER Korea, KODA) has procured 44 kind's assembly tools for ITER project. The assembly tools are classified by the steel structure, lifting table and lifting accessory. ‘PF 1, 6 and Central Solenoid Lifting Frame’ (CS Lifting Frame) and ‘Sector Lifting Tool’ (SLT) are the representative assembly tool classified the lifting accessory. The assembly tools handle the heavy component which over 1,000 tones for payload. In this reason, the verification of the strength of the tools is very important and the integrity of lifting accessory tools was verified by not only structural analysis but also load test at factory under 1.5 times the payload for minimum 15 min. It is the requirements of the technical specification. The main role of PF 1, 6 and CS Lifting Frame is to lift and transfer the ITER components (PF1 coil, PF6 coil and CS coil) from the assembly hall to the tokamak fit and their temporary support positions. The CS coil is heaviest component in payloads handled by CS Lifting Frame. The weight is about 1,000 tones and CS Lifting Frame was verified by 1,500 tones load test. Sector Lifting Frame is to lift and transfer the 40° sector module from Sector Sub-Assembly Tool (SSAT) to tokamak fit. The sector module consists of Vacuum Vessel (VV), VV Thermal Shield and Two Toroidal Flied Coils. The total weight of the sector module is about 1,300 tones and Sector Lifting Frame was verified by 2,000 tones load test. The load test was carried out according to test procedure approved by IO. This paper describes the overall test method, customized test JIG and result of the lifting tools for handling heavy components of ITER.

Study on the impact of non-silver coated area in the ITER vacuum vessel thermal shield

In the ITER tokamak, a thermal shield (TS) is installed to reduce the heat oad radiated to the superconducting magnet system from vacuum vessel (VV) and cryostat. TS has a thin silver surface to keep its emissivity below 0.05. The silver surface is achieved by electroplating. However, some vacuum vessel thermal shield (VVTS) may be imperfectly silver coated due to their complex geometry. When a segment of the VVTS is immersed in silver coating bath, electron is concentrated to the sharp edge of segment and doesn’t reach to the deep area. Also, solution in a segment surface for pre-treatment may not be removed in some point due to its geometry, and it disturbs the silver coating. In this paper, the impact of non-silver coating on heat loads from TS to magnet system is researched as following process; 1) Identification of area where the VVTS may be imperfectly silver coated – it is obtained from actual silver coating of ITER VVTS. 2) FE model/analysis condition construction of VVTS – VVTS solid element / cooling tube beam element is combined, and silver coated / non-coated area shell element with respective emissivity is applied. 3) Thermal analysis of VVTS with non-silver coated area – heat load via non-coated area of VVTS is calculated, and its impact to magnet system is estimated. According to thermal analysis of VVTS, the essential silver coating points to reduce heat load are identified. As remedial action is applied to the essential points, the heat load from VVTS to magnet system is minimized.

Manufacturing and welding assembly of the vacuum vessel on JT-60SA

The JT-60SA Vacuum Vessel (VV) was manufactured as the 10 sectors split in the factory and these sectors were weld-assembled as the 360-degree torus with the design offset value of the weld shrinkage. The dimensions as the 10 m scale torus were well controlled regardless of the thin wall thickness of 18 mm and a large amount of welding line due to the double wall structure and 72 port penetrations. The final VV 20-degree sector was installed into the 340-degree sector of the tokamak with the TF coil and the VV Thermal Shield, and the VV was weld-jointed as a torus. This paper reports the design concept to reduce the safety factor and welding amount to achieve the dimension specified, and the result of the VV manufacturing.

Progress on the manufacturing of ITER thermal shields

The role of the ITER thermal shield (TS) is to minimize the radiation heat load transferred from the warm components to the superconducting magnet operating at 4.5 K. Fabrication of the TS components is ongoing. Manufacturing of LCTS (Lower Cryostat TS) cylinder and VVTS (Vacuum Vessel TS) sector #6 was completed. The leak tightness of the cooling tubes, the on-site installation feasibility and the quality of the silver coated surfaces are main concerns during the manufacturing. Leak tightness of the cooling tubes is guaranteed by the test and the inspection. The surfaces of the cooling tube inside are inspected visually using the endoscope and the leak tightness has been qualified by the pressure and helium leak test. The on-site installation feasibilities are validated by the preassembly test at the factory. According to the qualified coating process, the TS panels are electro-plated with silver. This paper describes the manufacturing progress and the technical achievements.

Design and manufacturing of thermal shield for JT-60SA

The thermal shield (TS) of JT-60SA which is a superconducting tokamak, is installed to reduce radiation heat load from a vacuum vessel (VV), a cryostat vessel and ports at ambient temperature to superconducting coils at 4 K. The TS is double walled structure with He cooling pipe at 80 K, and is divided electrically in toroidal direction and poloidal direction to suppress eddy currents flowing through the TS during disruption. The TS is required to be installed in a narrow space which is between the VV, the ports, and the superconducting coils. Manufacturing and assembly accuracy of the TS are required to ensure the sufficient space for the relative displacement caused by thermal displacement and seismic load. Customization of mechanical joints in the divided section of the TS is effective process for keeping the required accuracy. Assembly of 340 ° sector of the vacuum vessel thermal shield has been completed.

Investigation on the in-situation pipe bending tool for the sector sub-assembly of ITER thermal shield

The main components of the ITER tokamak are assembled from the nine sub-assemblies of the 40° sectors. During the sub-assembly, the Toroidal Field coils (TFCs) are installed outside of the Vacuum Vessel Thermal Shield (VVTS) by rotation. The clearance between TFCs and VVTS is very narrow, in relation to the cooling tube end points, which are connected to the thermal shield manifolds. The dimensional analysis shows that in-situ bending of the VVTS cooling tube is required instead of pre-bending. This paper describes the development of the in-situ bending tool and its validations. The specialized tool is designed and the in-situ bending procedure is verified by structural analysis and mock-up test.

Fabrication and factory acceptance test of ITER sector sub-assembly tool

An ITER Tokamak machine with a torus shape is composed of nine units of 40◦ sectors. The sector sub-assembly tool (SSAT) is dedicated assembly tool to integrate vacuum vessel (VV) sector, VV thermal shield (VVTS) segments, VVTS port shrouds, two toroidal field coils (TFC) and various intercoil structures into 40◦ sector. For the sub-assembly process of 40° sector, SSAT shall have sufficient strength to support and handle heavy components up to 1250 t. And fine alignment system to adjust components considering assembly tolerance should be designed and verified by appropriate means. Although the structural analysis and mock-up tests were completed, structural stability and alignment system should be verified through factory acceptance test with real component and system. In this paper, the factory acceptance test results of the sector sub-assembly tool including VV load simulation and partial load test of VVTS outboard (OB) sector frame will be presented to verify the structural assessment and adjustment of the component.

Application of 3D View Factor method for heat fluxes deposition on ITER Cryostat Thermal Shield

The role of the ITER Tokamak thermal shield system is to minimize heat loads transferred from the hot tokamak components to the cooled superconducting components. The system consists of two single wall structures fabricated from 304L-(N) stainless steel. Both structures are actively cooled with pipes permanently welded to the structure and filled with pressurized helium gas at 80K. One structure is the Vacuum Vessel Thermal Shield (VVTS), which protects magnet components from Vacuum Vessel (VV) radiation. The second structure is the Cryostat Thermal Shield (CTS), which protects magnet components from in-Cryostat components’ radiations such as the Cryostat (at 293K), the VV Ports (at 393K), and the water cooling system (at 350K).In 2012, thermal analyses were performed in order to verify the thermal integrity of the ITER CTS 2010 baseline design. The heat loads to the CTS were estimated according to load specification as a homogeneous distribution based on cryostat temperature at 293K. Following this study, in order to determine a more realistic heat load distribution on the CTS panels, we performed a detailed 3D analysis of the Cryostat-CTS interspace.This paper describes the methodology used, based on view factors combined with Kirchhoff's law, to define the heat flux deposition on the CTS from its surrounding components via radiation. The previous thermo-hydraulic analysis models have been adapted using this method to define the temperature distribution and total power transmitted to the magnets. Despite an increase of 30% of the CTS total power deposition on the superconducting components in comparison to the previous analysis, we found the total heat power deposition onto the superconducting components at 4K to be within the limit of the design requirement (P≤1900W).

Manufacturing progress of first delivery sector of ITER vacuum vessel thermal shield

This paper describes the manufacturing progress of ITER Vacuum Vessel Thermal Shield (VVTS) sectors, which are on-going since the start of material buffing in October 2014. Fabrication of VVTS proceeds according to the following main processes: 1) plate cutting, 2) bending and forming, 3) welding, 4) flange final machining, 5) pre-assembly of 40 ° sector, 6) silver coating and 7) final acceptance test. All VVTS shell segments are to be assembled by the flange joints, which are welded to the shells. Two kinds of inspection methods are presented for the cooling pipe welding: endoscope and leak test. A specific endoscope is developed for a long welded cooling pipe. Vacuum leak test is performed in the test vacuum chamber with the helium pressurization of cooling pipe by 3 MPa, which is the same pressure differential with the operating condition of the VVTS. One of the dimensional inspection, 3D laser scanning is also described to see the effect of shape correction for the flange to shell welding. Silver coating jig design has been carried out, focusing on the electrode position. Structural analysis results are shown for the design of pre-assembly jig of 40 ° sector. Finally near term schedule of the manufacturing is summarized.

Structural analysis for final design of ITER sector sub-assembly tool

The Sector Sub-assembly Tool is a special tool for assembly of ITER Tokamak and is used to sub-assemble the 40° Tokamak sector which consists of vacuum vessel sector, vacuum vessel thermal shield sector and two toroidal field coils. The sector assembled in the assembly building is a basic and fundamental unit for the construction of the ITER Tokamak. The functions of the Sector Sub-assembly Tool are to support and handle heavy components which weigh up to 1200t. The Sector Sub-assembly Tool is one of the most important tools to perform the assembly of ITER. To assess the design and structural integrity of the Sector Sub-assembly tool, the structural analyses have been performed under the load combinations according to load specifications. The results of the structural analyses show that the stresses of the Sector Sub-assembly Tool are below the allowable stress. This paper provides briefly the result of structural analysis for the Sector Sub-assembly Tool.

Thermal radiation analysis of DEMO tokamak

Thermal radiation analysis of the DEMO tokamak based on the 2015 baseline CAD design model was performed. For the purpose of analysis, Vacuum Vessel Thermal Shield (VVTS) and Cryostat Thermal Shield (CTS) were designed on a conceptual level to complement the baseline DEMO CAD model. The Finite Element (FE) code ABAQUS was used to perform numerical analyses. A special care was taken to adapt the geometry and mesh of the FE model to reduce the heat transfer error to an acceptable level. Thermal loading on DEMO components and refrigeration power for the base case scenario with actively cooled thermal shields was determined. Besides the base case, the sensitivity analysis with passive CTS was performed.

Acceleration of calculation of nuclear heating distributions in ITER toroidal field coils using hybrid Monte Carlo/deterministic techniques

Because the superconductivity of the ITER toroidal field coils (TFC) must be protected against local overheating, detailed spatial distribution of the TFC nuclear heating is needed to assess the acceptability of the designs of the blanket, vacuum vessel (VV), and VV thermal shield. Accurate Monte Carlo calculations of the distributions of the TFC nuclear heating are challenged by the small volumes of the tally segmentations and by the thick layers of shielding provided by the blanket and VV. To speed up the MCNP calculation of the nuclear heating distribution in different segments of the coil casing, ground insulation, and winding packs of the ITER TFC, the ITER Organization (IO) used the MCNP weight window generator (WWG). The maximum relative uncertainty of the tallies in this calculation was 82.7%. In this work, this MCNP calculation was repeated using variance reduction parameters generated by the Oak Ridge National Laboratory AutomateD VAriaNce reducTion Generator (ADVANTG) code and both MCNP calculations were compared in terms of computational efficiency and reliability. Even though the ADVANTG MCNP calculation used less than one-sixth of the computational resources of the IO calculation, the relative uncertainties of all the tallies in the ADVANTG MCNP calculation were less than 6.1%. The nuclear heating results of the two calculations were significantly different by factors between 1.5 and 2.3 in some of the segments of the furthest winding pack turn from the plasma neutron source. Even though the nuclear heating in this turn may not affect the ITER design because it is much smaller than the nuclear heating in the turns that are closer to the plasma source, it is our recommendation to adopt the utilization of ADVANTG in similar calculations to increase the reliability of MCNP calculations of detailed distributions of nuclear responses.

Progress of the ITER Thermal Shields

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 4.5K. 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.

Fabrication of full-size mock-up for 10° section of ITER vacuum vessel thermal shield

In this paper, a full-scale prototype fabrication for vacuum vessel thermal shield (VVTS) of ITER tokamak is described and test results are reported. All the manufacturing processes except for silver coating were performed in the fabrication of 10° section of VVTS. Pre-qualification test was conducted to compare the vertical and the horizontal welding positions. After shell welding, shell distortion was measured and adjusted. Shell thickness change was also measured after buffing process. Specially, VVTS ports need large bending and complex welding of shell and flange. Bending method for the complex and long cooling tube layout especially for the VVTS ports was developed in detail. Dimensional inspection of the fabricated mock-up was performed with a 3D laser scanner and the scanning data was analyzed.

Final design of ITER vacuum vessel thermal shield

The final design of ITER vacuum vessel thermal shield (VVTS), which is planned to be procured completely by Korea, has been implemented after the procurement arrangement was signed. In this paper, the design and the supporting analysis are described for the key components of the VVTS such as joint, panel, support, and stopper. The VVTS design is revised and finalized based on the manufacturing feasibility, interface requirement and assemble feasibility. The inboard and the outboard supports of VVTS are designed in detail considering structural rigidity and assemble feasibility. The shape of in-pit joint, which is installed every 40° sector in toroidal direction for compensation of possible misalignment during sector assembly, is determined. Three types of joints are developed in accordance with their locations and assemble feasibilities are checked through the R&D. Stopper design is developed in order to prevent direct contact against adjacent components such as vacuum vessel and magnets. Structural rigidity of the whole VVTS is also validated by finite element analysis under various kinds of operating conditions, such as deadweight, electro-magnetic load, seismic load and load combinations.

Fabrication of a full-size mock-up for inboard 10° section of ITER vacuum vessel thermal shield

A full-scale mock-up of VVTS inboard section was made in order to validate its manufacturing processes before manufacturing the vacuum vessel thermal shield (VVTS) for ITER tokamak. VVTS inboard 10° section consists of 20 mm shells on which cooling tubes are welded and flange joints that connect adjacent thermal shield sectors. The whole VVTS inboard is divided into two by bisectional flange joint located at the center. All the manufacturing processes except silver coating were tested and verified in the fabrication of mock-up. For the forming and the welding, pre-qualification tests were conducted to find proper process conditions. Shell thickness change was measured after bending, forming and buffing processes. Shell distortion was adjusted after the welding. Welding was validated by non-destructive examination. Bisectional flange joint was successfully assembled by inserting pins and tightening with bolt/nut. Bolt hole margin of 2 mm for sector flange was revealed to be sufficient by successful sector assembly of upper and lower parts of mock-up. Handling jig was found to be essential because the inboard section was flexible. Dimensional inspection of the fabricated mock-up was performed with a 3D laser scanner.

The design of the assembly tools for the ITER tokamak

The conceptual design of the purpose-built assembly tools required for ITER tokamak assembly is given. The ITER machine assembly is sub-divided into five major activities: lower cryostat, sector sub-assembly, sector assembly, ex-vessel, and in-vessel [1]. The core components, vacuum vessel (VV) and toroidal field coil (TFC), are assembled from nine 40° sub-assemblies, each comprising a 40° VV sector, two TFCs, and the associated VV thermal shield (VVTS). The lower cryostat activities must be completed prior to sector assembly in pit to prepare the foundations for the core components, and to locate the lower components to be trapped once the core components installation begins. In-vessel and ex-vessel activities follow completion of sector assembly. To perform these assembly activities requires both massive, purpose-built tools, and standard heavy handling and support tools. The tools have the capability of supporting and adjusting the largest of the ITER components; with maximum linear dimension 19 m and mass 1200 tonne, with a precision in the low mm range. Conceptual designs for these tools have been elaborated with the collaboration of the Korean Domestic Agency (KO DA). The structural analysis was performed as well using ANSYS code.

Progress of detailed design and supporting analysis of ITER thermal shield

The detailed design of ITER thermal shield (TS), which is planned to be procured completely by Korea, has been implemented since 2007. In this paper, the design and the supporting analysis are described for the critical components of the TS, the vacuum vessel TS (VVTS) outboard panel, labyrinths and VVTS supports. The wall type of VVTS outboard panel was changed from double wall to single wall, and the verification analyses were carried out for this design change. The dimensions of the labyrinths were determined and the heat load through the labyrinth was analyzed to check the design requirement. The preliminary result of the VVTS inboard and outboard supports were obtained considering the structural rigidity.

Technical diagnosis system for EAST tokamak

Technical diagnosis system (TDS) is one of the important subsystems of EAST (experimental advanced superconducting tokamak) device, main function of which is to monitor status parameters in EAST device. Those status parameters include temperature of different positions of main components, resistance of each superconducting (SC) coils, joint resistance of SC coils and high-temperature superconducting (HTS) current leads, strain of cold-quality components endured force, and displacement and current of toroidal field (TF) coils in EAST device, which are analog input signals. In addition there are still some analog and digital output signals. The TDS monitors all of those signals in the period of EAST experiments. TDS data monitoring is described in detail for it plays important role during EAST campaign. And how to protect the SC magnet system during each plasma discharging is presented with data of temperature of coolant inlet and outlet of SC coils and feeders and cases of the TF coils and temperature in the upper and middle and bottom of the TF coil case. During construction of the TDS primary difficulties come from installation of Lakeshore Cernox temperature sensors, strain measurement of central solenoid coils support legs and installation of co-wound voltage sensors for quench detection. While during operation since the first commissioning big challenges are from temperature measurement changes in current leads and quench detection of PF coils. Those difficulties in both stages are introduced which are key to make the TDS reliable. Meanwhile analysis of experimental data like temperature as a back up to testify quench occurrence and stress on vacuum vessel thermal shield and vacuum vessel have also been discussed.

A conceptual design and structural stabilities of in-pit assembly tools for the completion of final sector assembly at tokamak hall

The final assembly of main components of the International Thermonuclear Experimental Reactor (ITER) tokamak, Vacuum Vessel (VV) and Toroidal Field Coils (TFCs), is achieved by the sequential assembly of the nine sub-assembled 40° sectors in tokamak pit. Each sub-assembled 40° sector is composed of one VV 40° sector, two TFCs, and in-between Vacuum Vessel Thermal Shield (VVTS) segments. Sub-assembly is carried out in the assembly building and then the sub-assembled sectors are transferred into tokamak pit, in sequence, to complete sector assembly. The role of in-pit assembly tool is to support and align the sub-assembled sectors in tokamak pit. It also plays the role of reference datum during assembly until the completion of main components assembly. Korea Domestic Agency (KO DA) has developed the conceptual design of most ITER purpose-built assembly tools under the collaboration with the ITER Organization. Among the conceptual designs carried out, this paper describes the function, the structure, the selected material and the design results of the in-pit assembly tools comprising central column, radial beams and their supports, TF inner supports and in-pit working floor. The results of structural analysis using ANSYS for the various loading cases are given as well. The resultant stresses and deflections turned out to fall within the allowable ranges.