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PROGRESS OF ITER-INDIA ACTIVITIES FOR ITER DELIVERABLES- Challenges and mitigation measures

1,2A.K.Chakraborty, 1,2Ujjwal Baruah, 1,2Aparajita Mukherjee, 1,2S.L.Rao, 1,2,3Vinay Kumar, 1,2Ajith Kumar, 1,2Girish Gupta, 1,2Hitensinh Vaghela, 1H.A.Pathak, 1,2Hitesh Pandya, 1,2,3Indranil Bandyopadhyay, 1,2,3Shishir Deshpande 1ITER-India, Institute for Plasma Research Gandhinagar - 382428, India. 2Institute for Plasma Research (IPR) Gandhinagar – 382428, India. 3Homi Bhaba National Institute (HBNI) Mumbai 400094, India. Email: arunkc@iter-india.org Abstract

Successful construction of ITER is dependent on the meeting of requirements on the supplies delivered to ITER from different domestic agencies at the component level and also at the level of functionality, when integrated. The responsibilities of ITER-India include a mix of precision, heavy, R&D intensive and interface intensive systems, under built-to-print and functional systems category. In several systems, components fall under the category of first of its kind or of the largest kind. The uniqueness of specifications leads to a challenging situation – namely that neither the existing labs or potential suppliers have ever done or encountered such scale-up (either in size/volume, capacity, precision etc.) and do not have even the R&D infrastructure to match the requirements. Under a graded approach a full-scale prototype or at an appropriate scale needs to be developed apart from the testing infrastructure. Facilities have been established to demonstrate the integrated and functional performance in the first if its kind and R&D intense systems, as a risk mitigation strategy. Attributes of uniqueness and the spectrum of activities, enables an opportunity to position the R&D activities as aligned with the needs of a fusion device. It also enables an opportunity to the industry to align their production process and assimilate the learning experience from the manufacturing activities for ITER deliverables, to application areas that blend technologies with stringent quality controls. While this learning experience on the ITER frame is applicable to industries on a global basis, to the Indian industry, it provides an opportunity to demonstrate its readiness to deliver, in a competitive frame, on technology products, meeting all requirements of international quality standards. A summary of the technical features in the major areas of procurements and notable achievements in R&D and manufacturing and their application in the Indian R&D related to fusion, is presented in the paper.

1. INTRODUCTION

Indian participation in ITER has the dual objective of propelling research to the frontier areas of fusion science and technology and to establish manufacturing process, procedures and practices in the industries that are compliant with the requirements of an international nuclear facility. The procurement responsibilities encompass the machine and several important services. They manifest in form of the following:

i. Cryostat – the 30 m dia, 30 m tall, outer shell of the ITER; ii. In wall shielding blocks, placed in between the two walls of the double walled vacuum vessel, to provide

the necessary neutron shielding; iii. Additional Heating and current drive systems

a. 20 MW RF source for Ion Cyclotron Resonance Heating, b. 2 Gyrotrons, each having a power delivery of 1 MW, c. A Diagnostic Neutral Beam System delivering 100 keV Hydrogen beams of ~ 20 A of Neutral

equivalent current to the ITER device, d. High voltage power supply systems supporting the operation of a-c, above;

iv. Cryolines and cryo distribution system to supply liquid and gaseous Helium at 4.2 K and 80 K from the cryogenic refrigerator to the magnetic field coils of ITER and other subsystems like cryo pumps;

v. Component Cooling water systems – providing cooling water supply to different clients in the form of a complete distribution loop;

vi. Diagnostics systems, consisting of X-ray survey spectrometer, ECE diagnostics and a part of the CXRS diagnostics.

In consideration of the nuclear regulatory requirements, the systems and components that interface with the primary vacuum boundary, the Tokamak building, and services that connect to the ITER device, have been

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classified as Safety Important components, whose manufacturing involves nuclear codes and includes regulatory surveillance, for their compliance. All other systems have to address to the requirements of nuclear device and is subject to the ITER procedure of Quality Assurance and Quality Control, in addition to the conformance with respect to stipulated codes and standards.

A unique aspect of ITER deliverable is the status of ‘first of its kind’ that applies to several systems and components, leading to R&D on such systems and components in the industrial and laboratory scale. For the Indian deliverables, they apply to:

I. Test facility for RF systems: a) Development of ICRF sources for 1.5 MW for 3600 S and a power of 3MW when integrated with a combiner, b) Test facility for establishing reliable performance of Gyrotorn

II. Development of Negative ion sources for ~ 60 A of accelerated current and transport to distances >20m, III. Development of special diagnostics system that interfaces with the nuclear envelope; IV. Development of multi process cryolines and special cryogenic pumps for supply of 3kg/s for the super

critical Helium flow. V. The manufacturing design of Cryostat, where processes required for carrying out UHV compatible

welding 20 - 200 mm thick plates of lengths of 100s of m; VI. Development of special process for the manufacturing of components of neutral beam injectors

VII. Performing important validations for the manufacturing of the In Wall Shield (IWS) for ITER

In each of the specific areas mentioned, dedicated R&D have been instituted and the activities undertaken for ITER forms a part of the larger program of sustained domestic R&D in important areas of magnetic fusion. Many of the process and practices that have emerged out of the R&D program for ITER have formed inputs to such domestic program and significant progress have taken place in areas of development of diverter technologies, cryo sorption pumps, magnets and materials. These would be covered in a separate submission.

This paper presents an overview of the R&D program, their outcome, results and relevance to ITER. The paper also presents an overview of the developments in areas of technology, in industry, their successful outcome and application to ITER.

Section 2 presents the specifics of the R&D programme. Section 3 presents manufacturing technology development and a short description of the hardware that applies domain expertise. Section 4 presents a short perspective on risk assessment and its mitigations. A summary is placed in Section 5.

2. R&D- ITER-INDIA LABORATORY

2.1 ICRF Systems

The mandate for the IC H&CD system is to deliver 20 MW to the ITER plasma in the frequency band of 40-55 MHz. To achieve 20 MW, a power of 24 MW is required at the output of the RF sources. This shall be produced from 8 RF sources, with each source having the power handling of 2.5 MW at VSWR of 2:1 in the frequency range of 35-65 MHz, or 3 MW at VSWR of 1.5:1 in the frequency range of 40-55 MHz. No unique amplifier chain is available to meet the output power specifications. For ITER, a new layout has been proposed with two parallel, three stage amplifier chain with a combiner circuit on the output side.

Keeping in view the gap between the demonstrated capability of RF source system, an R&D program with the mandate to prove the delivery of 2.5/3 MW RF power from the two parallel, three stage amplifier chain, has been launched. For this purpose, a dedicated high power test facility, consisting of a wide band solid state amplifier (for 35 – 65 MHz, 10 kW) as pre-driver stage, high voltage power supplies (Maximum voltage/current 27 kV/ 190 A), high power transmission lines (12’’), a 3MW, water cooled dummy load, and a local control unit for control and monitoring (approx. 150 analog and digital channels). Demonstration of each chain having the specification of delivering 1.5 MW for 2000s in the 35-65 MHz, at VSWR of 2:1, was the aim of this R&D activity.

Both Diacrode and Tetrode technologies have been considered from the two leading manufacturers of the world. The Diacrode based system along with the power supplies, controls, cooling etc. have achieved 1.5 MW of RF power for more than 2000s, in the frequency range of 35 – 65 MHz. An output power with VSWR condition (upto 2:1) at any phase angle, thereby ensuring constant power to the ITER plasma during ELMS, has been

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demonstrated. For this, the RF source was operated for mismatched load conditions at various reflection angles (0, 45, 90, 135, 180 degrees). Forward power could be kept constant at 1.5 MW, with reflection levels of 11%, thereby demonstrating VSWR 2:1, which creates an important database for ITER. The Diacrode has been subjected to a burn test for 6000s continuously to verify the ruggedness and benchmark the technology for fusion application [1].

The Tetrode based system is also subjected to acceptance test procedure similar to that of the Diacrode system. The test for ruggedness has been conducted by operating 5 consecutive shots of 2000s each with 25% duty cycle at 1.5 MW power level [2]. The results of the performance are shown in Fig. 1 and Fig.2 for Tetrode and Diacrode based system respectively.

The next immediate objective after this R&D program is of achieving 2.5 MW at VSWR 2:1 in the frequency range of 35-65 MHz, by combining two RF amplifier chains using a wide band combiner and carrying out tests for ITER like scenarios, the integration scheme for this test is shown in Fig. 3.

FIG. 1. Tetrode based system 1.7MW/36MHz/3600s on matched load (a) Run test, (b) BW on spectrum analyser.

FIG. 2. Diacrode based system 1.7MW/36MHz/3600s on matched load (a) Run test, (b) BW on spectrum analyser.

FIG. 3. Schematic of integration scheme

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2.2 EC Systems

In the EC system, India is responsible for providing 2 gyrotrons sources of 1 MW power output at 170 GHz for 3600s pulse length [3]. Establishing the reliable, integrated system performance is the primary objective of the Gyrotron Test Facility (GTF) which is currently under development at ITER-India. The test facility is being developed with prototype auxiliary systems including a set of dedicated high voltage power supplies to ensure that the test facility configuration and the environment is close to that of the ITER deliverables. A dedicated 55kV, 110A, PSM based Main High voltage power supply for the gyrotron cathode circuit is in advanced stage of development. A prototype of compact cost effective solution using solid state switch has been prepared and tested as a potential solution for the low current fast switching high voltage gyrotron body power supply. Apart from ensuring the provision for power supplies for the high and medium voltages and cooling provisions, specific emphasis has been placed on the integration of the Local Control unit (LCU) where critical interlock and protections requiring fast interlocks (<10 µs) are implemented. For this fast interlock protection, two field based interlock modules, Distributed Interlock Module (DIM) and Centralised Interlock Module (CIM) are developed with a redundancy option on one of them. A Gyrotron field simulator has been incorporated to validate the LCU functionality and improve the reliability of the overall system. The diagnostics of this GTF includes a long pulse RF dummy load based on water calorimetric measurements and a short pulse dummy load where pulse integration technique would be used to estimate the power. For instantaneous RF power monitoring, a calibrated Schotky diode, mounted on waveguide directional coupler, would be used. The power sampled through the coupler will also be used to monitor the frequency. In order to estimate the gyrotron output beam mode purity, an IR camera based mode purity diagnostics will be used where the indirectly measured beam amplitude data will be analysed using phase retrieval techniques to estimate the mode purity. The GTF shall be operational, following the delivery of an ITER relevant Test Gyrotron which is currently under procurement.

2.3 Diagnostic Neutral Beams

The negative Hydrogen ion based diagnostic Neutral Beam (DNB) is mandated to deliver ~ 20 A of Neutral Equivalent beam of Hydrogen at 100 keV energy. The Ion source is RF based where 4 RF generators operating at 1 MHz each provide input power up to 800 kW to the 8 drives. The accelerator section accelerates 60 A of ion beam current for subsequent neutralization and transport of the neutralized fraction, after separation of residual ions, to the Tokamak.

The production of 60 A of accelerated current @ 35 mA/cm2 of extraction current density, from the beam source would be a challenge. The performance also demands a stringent control on the ion optics, which, in turn is related to the manufacturing accuracies. Additionally, the electrostatic ion separation and transport of the beam over lengths >20 m, are the physics and engineering challenges in the beam line.

A dedicated test facility has therefore been created to test the performance of the beam source and transport for the DNB system. The facility, christened as the Indian Test Facility (IN-TF) [4][5][6] shall test the deliverable parameters for the DNB and component procurement for DNB has been accelerated to enable the operation of this facility. Fig. 4 shows the schematic of this facility.

FIG. 4. INTF beamline layout schematic.

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The production of characterization of high current Negative ion sources is an important subject of study, in particular for the ITER NB systems. Operation of a single driver based source has been established in IPP Garching [7], which has been followed up by the operation of a source ELISE, which is half of the size of ITER and performance parameters have been optimized in ELISE [8] for Hydrogen operation. Additionally, the SPIDER source has been operational [9] in the ITER NB Test facility, Padova. The Indian R&D program has adopted an approach where the first stage has been that of commissioning a single driver based source ROBIN (replicating the IPP Garching BATMAN) [10]. ROBIN has demonstrated an extracted current of density 27 mA/cm2. Fig.5 presents a representative shot from ROBIN, depicting the achieved current density, the applied RF power at a source filling pressure of ~0.5 Pa. Efforts are ongoing to increase the current density to higher values.

FIG. 5. Typical ROBIN shot with 27 mA/cm2 current density.

ROBIN is followed by the commissioning of a two driver source, TWIN [11], which is an indigenous development, mandated for operational studies on multi driver coupling from a single source. A 180 kW RF Generator, operating at 1 MHz, provides the necessary input power to the twin drivers of this source. The source is presently in its operational integration stage.

The Test facility of IN-TF is expected to begin its operation following the integration of the beam source, expected by the last quarter of 2019. Manufacturing of the beam source involves several challenges as will be discussed in the technology section.

2.4 Diagnostics

The responsibilities under Diagnostics include the following: i) X-ray crystal spectroscopy (survey (XRCS-Survey)- to monitor plasma impurities in the range of 0.1 – 10 nm & edge (XRCS-Edge) – to measure profiles of ion temperature and plasma rotation) ; ii) Electron Cyclotron Emission (ECE) includes the transmission line and receiver for 70 GHz to 1 THz; iii) Charge Exchange Recombination Spectroscopy (CXRS-P) to measure Helium ash and iv) Upper port UP-09, to house XRCS and other diagnostics.

2.4.1 R&D on ECE Diagnostics

The challenges in the ECE diagnostics are in the transmission of low power calibration signals over the frequency range of 70 GHz to 1 THz, with low attenuation over distances of 40-50 m and in the development of a Fourier Transform Spectrometer (FTS) with high throughput and fast scanning mechanism in the vacuum.

The high temperature blackbody source required for characterizing the measuring instruments of the ECE diagnostics – Michelson Inteferometer and radiometer, have been developed for the wave length of 100 GHz to 1 THz. This Silicon Carbide (SiC) source has a short and long term temperature stability in the range of +/- 2 ⁰C and +/-10 ⁰C and a microwave emissivity has been observed over the band of 0.8 – 0.9 over the aforesaid frequency range.

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For the characterization of (FTS) for high throughput and a fast scanning, a prototype experiment, shown in Fig. 6, has been set up and attenuation in the evacuated transmission line – spectrometer combination, has been measured to be within 15 – 22 dB. The experiment has been carried out on a wave guide section of 8 m, with 2 miter bends and the results provide a calibration methodology.

FIG. 6. Experimental set-up for prototype and SiC source

2.5 Cryo-distribution and Cryo-lines (CDCL)

2.5.1 Transfer lines

The cryolines for the ITER project are vacuum jacketed, multi process pipes and need to be qualified for layout, allowable heat load, manufacturing and integration feasibility, various load cases for ITER, safety and regulatory requirements. A dedicated Prototype Cryoline (PTCL) test facility has been set up to test and qualify a scaled section of 29 m of prototype cryoline, consisting of six process pipes with an outer vacuum jacket of 600 mm diameter and carrying helium at 4.5 K and at 80 K. The layout includes the 90 degree and 160 degree bends, Tee elements, out of plane section and straight elements. Two PTCLs, i.e., PTCL-1 and PTCL-2 from two different suppliers were manufactured and tested at PTCL test facility in ITER-India cryogenic laboratory [12] [13]. Fig. 7 shows the PTCL-1 and 2 installed in the ITER-India Cryogenics Laboratory.

FIG. 7. PTCL-1 and 2 in installed condition at ITER-India cryogenic laboratory.

The tests established the following: a global leak rate between process pipes to vacuum insulation of the order 10-10 mbar l/s and from atmosphere to insulation vacuum of the order 10-6 mbar l/s, successful pressure test as per PED requirements, mechanical integrity during cryogenic cold test, average maximum temperature <90 K on thermal shield and heat load within the specification of 33.5 W at 4.5 K and 126 W at 80 K. Additionally, temperature measurements have been carried out, using cryogenic temperature sensors, on the thermal shields, internal supports to ensure conformity of the design with respect to the design of manufactured assembly. Tests have also been carried out for beak of insulation vacuum conditions, wherein, the lowest temperature on the OVJ and thermal contraction of OVJ were validated. The tests carried out above provided confidence in the design and manufacturing processes and led to the initiation of bulk production of cryolines for ITER, which, presently is in the stage of delivery.

2.5.2 Cryodistribution

The Cryodistribution system supplies the Supercritical Helium (SHe) to the superconducting magnets of ITER Central Solenoid (CS), Toroidal Field Coils (TF) and Poloidal Field (PF) Coils, magnet support structure as well as to the cryo pumps. The principal challenge in cryodistribution is the development of clod circulators having mass flow rate of the order 3 kg/s at 4.3 K and 0.15 MPa pressure head. Cold circulators of this rating were not available and required a special development and testing. Two manufacturers having competitive technologies, based on active magnetic bearing and hybrid ceramic ball bearing [14] have designed and manufactured the test

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cold circulators. A dedicated test has been carried out for the cold circulators in the cryogenic facility of JAEA. A Test Auxiliary Cold Box (TACB) has been installed into the JAEA cryogenic facility for the test purpose. The tests established all modes of operation and performance of both types of cold circulators at nominal and maximum operational condition and characterization have been demonstrated for mass flow rates > 3 kg/s, within a pressure head of 219 kPa, ensuring reliable cryogenic distribution to the CS, TF and PF magnets and cryopump. Presently, manufacturing of the main series for ITER cryo distribution is in progress.

2.6 Summary of R&D- ITER-India laboratory

The developments stated above have led to the setting up of R&D facilities in the respective areas that are of the state of the art. The outcome of R&D have provided the necessary confidence to ITER about the system configuration and ensures availability of hardware for the operational phases. Additional efforts have been invested under the domestic program of the Institute for Plasma Research to undertake additional developments in areas on divertor technologies, material and technologies necessary for the test blankets, development of magnet technology and development of cryosorption pumps. These activities have generated the requisite expertise in important areas of R&D in magnetic fusion.

3. R & D- CARRIED OUT WITH INDUSTRIES ON MANUFACTURING TECHNOLOGIES

The manufacturing of components for ITER involves a wide spectrum ranging from high end precision fabrication, to extremes of fabrication in heavy engineering. Each end of the spectrum offers their unique form of challenges. In some cases, prototyping activity has formed a part of the contract agreement for the purpose of establishing the achievable specifications, on components of significant complexity. Additionally, specific tasks have been undertaken for the development of complex materials, performing studies on corrosion resistance, developing welding technologies etc. The results of these development have been applied to the procurement, as summarized below.

3.1 Cryostat

Cryostat, the outer vacuum shell of ITER, is a single wall vacuum vessel of weight 3000 Ton, ~ 29 M in diameter and ~ 29 m in height. Being a Protection Important component (PIC – 2), the fabrication needs to follow the French Quality Order, which includes documentation and traceability. Due to limitations on road transport and the need for assembly of ITER device, within the Cryostat, the Cryostat has been divided into four sections of Base, Lower Cylinder, Upper Cylinder and Top lid. Each section, other than the Top lid, is divided vertically into two tiers and each tier has six sectors in the Toroidal plane. The Top lid is divided into thirteen sectors. The construction is heavily dependent on welding across different thickness, ranging from 20 mm to 200 mm and control of weld distortion, to remain compliant with ITER specifications, is the principal challenge in the fabrication of the Cryostat.

This is primarily due to the fact that, properties of low thermal conductivity and high thermal expansion in Austenitic Stainless Steel, make it difficult to maintain the shape, particularly in the welding of thick sections, where temperature gradient plays a major role. Hence, it was necessary to establish the procedure and a 400 sector of the Base section Tier-2 mock-up has been undertaken to achieve a control over flatness within 12 mm for 200 mm thick plates of pedestal ring, on which, welding has been performed. Fig. 8 shows the mock-up assembly. The procedure followed is of pre-cambering, for the fabrication of the top and bottom plates separately, followed by appropriate sequencing, to ensure that the flatness is controlled within 3 mm. Following this, the inner and outer plates are welded on the bottom plate and the final welding was performed on the top plate and the final assembly remained within 3 mm, i.e. the limits allowed for distortion.

FIG. 8. Base section Tier-2 mock-up

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This procedure has been applied to the Tier -2 of each 60⁰ sector of the base section and flatness control, within 12 mm has been achieved. In a similar manner, a mock-up of the lower cylinder was planned to achieve the final profile requirement of 100 mm at Tokamak pit. For this, a target was set to achieve a profile of 35 mm at the factory stage. The mock-up considered is for a 60⁰sector of the lower cylinder, as shown in Fig. 9 (a). The first attempt, due the long arc length of 15 m on the 50 mm thick section, did not lead to the expected profile. Further segmentation was done and the two halves of 30⁰ have been welded from both sides, by a balanced welding approach, leading to control of profile within 20 mm on the 60⁰ sector. The procedure has been applied to the manufacturing of the 60⁰ sectors of the Cryostat lower cylinder, using this methodology and profile control has been achieved, within 35 mm. A mock-up for the top lid is presently in progress.

The on-going fabrication Cryostat have led the establishment of additional technologies for: i) development of dual operator technique to control distortion in T welds, ii) development of special Hot wire TIG welding for heavy thickness welds to be carried out at site (Fig.9 (b)), iii) Development of weld inspection by Ultrasonic method for thick welds.

FIG. 9. (a) Mock-up for Lower cylinder (b) NG TIG welding on TOP Plate

The processes developed has been applied effectively to the production. A special workshop has been erected within the ITER site to facilitate the fabrication of large sections and their corresponding transfer to the ITER building. Assembly and welding of the base section and lower cylinder is currently in progress in the site Cryostat workshop.

3.2 Diagnostic Neutral Beam (DNB) – Manufacturing Technologies

Realisation of precision manufacturing is the principal challenge in the manufacturing of components for DNB [6], in particular the beam source. For the accelerator of the beam source [15], precision of aperture positioning accuracy of 20 µm, flatness within 0.020mm mm and angular accuracies within 0.002⁰ over lengths of ~ 0.6 m is a challenge even for the most advanced manufacturing industries. A prototype phase initiated early in the project has led to the realizable set of specifications: Aperture positioning of 50 µm, flatness within 0.040mm and angle within +/-0.002⁰. Fig. 11 shows the manufactured accelerator segment for ITER. This angled grid is the first such manufacturing and has generated the requisite experience which is applicable to the manufacturing of the Heating Neutral Beams (HNB) as well.

FIG. 11. Manufactured Plasma Grid segment

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Another important area of technology has been the development of ITER Grade Copper Chromium Zirconium (Cu-Cr-Zr) alloy, which is used extensively in the beam line components of ITER neutral Beams (DNB and HNB). The material has been produced without the use of metalloid deoxidizer, to guarantee the minimum Oxygen level. As shown in Fig. 12, the development has followed a methodical plan, where 77 heats of Cu-Cr-Zr has been produced in 4 lots, and has led to the production of material that conforms fully to the ITER grade (Chemical properties: Cu: 0.6-0.9; Cr: 0.07-0.15; Zr: 0.07-0.15; O<0.0025; Co<0.05; Cd<0.005; Si<0.1; Fe<0.08, Mechanical properties: UTS-384MPa @20 ⁰C and 263MPa @350 ⁰C with conductivity >75%IACS). This material is used in the production of Beam Line Components (BLC) for DNB.

FIG. 12. Analysis of Cr & Zr in various heats

Additionally, technologies have been developed for the full penetration Electron Beam Welding (EBW) of the dissimilar transitions from CuOF to SS and Cu-Cr-Zr to SS 316L, through an intermediate nickel / Inconel inset. Repeatability has been established after repeated trials, for pipe to pipe, pipe to plate and plate to plate configurations. The weld has been characterized with tensile, bend tests and micro and macro examinations with hardness survey, as shown in the Fig. 13 below.

FIG. 13. Deep drilled panels and Micro and macro examinations with hardness survey

Full size components have also been prototyped for the long length (1.7 m), high precision (drift control within 0.5 mm over the length of ~1.8m) deep drilling operation, where a special tool with inbuilt arrangement for circulating the cooling fluid has been developed. These successful developments enabled an effective and better technical coordination with the manufacturer, responsible for the bulk fabrication.

3.3 In-wall Shield

The In Wall Shield (IWS) blocks are placed in between the two walls of the ITER vacuum vessel and 8809 blocks are to be assembled for the 9 sectors of vacuum vessel and the field joints in between the sectors. The blocks are assemblies of machined plates, each of which is 40 mm thick, made out of borated steel and Ferritic steel. There are about 58000 plates which are to be machined to precision, involving 3-D profiles. The work of block assembly uses ~ 1,50,000 brackets, spacers, bolts and washers.

R&D was carried out to establish the corrosion impact on the materials of these blocks, as these blocks remain inaccessible, due to their permanent placement in between the walls of the vacuum vessel [16][17]. The corrosion study shows that there is no pitting under conditions of water temperature 100⁰ C and 1.1 MPa pressure, whereas

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pitting is evidenced in the operating conditions of water temperature of 200⁰ C and pressures of 2.4 MPa. The critical pitting temperature is between 100⁰ C and 200⁰ C. However, the maximum corrosion rate that is observed for SS430 which is about of 0.276 mm/year (measured by loss of weight technique), which is acceptable for the ITER life cycle. Additionally, tests were also carried out to ensure that no corrosion induced degradation of the outgassing rate for hydrogen occurs beyond the permissible limit of 1x10-7 Pam3s-1m2.

Additionally, a block assembly has been subjected to vibration study, within the operating range of ITER, to ensure that there is no reduction in preloading of fasteners of the block assembly due to vibrations. A preload of 104 kN was applied to the M30 bolts and the cap screws were preloaded to 23 kN, in accordance with the electromagnetic force that applies during plasma operation. The tests have been carried out on tri-axial shaker system with 6 degrees of freedom, simulating the actual operating conditions of the ITER vacuum vessel. The blocks were subject to a range of vibration frequencies and acceleration. No change in the values of the strain was observed and a subsequent Liquid Penetrant Test (LPT) confirmed no damage on the spot welds after the tests. Fig. 14 shows the block assembly that has been subject to vibration tests.

FIG. 14. IWS Block assembly under vibration test

The SS 304 B7 material for the blocks have been manufactured by the powder metallurgy route, to ensure a better grain structure and boron distribution.

Fabrication involves water jet cutting and extensive CNC machining. LPT and UT are main NDT used for raw material and weld inspection during production. The production rates required for IWS is high and quality inspection involves application of CMM with a high speed, and application of LPT on a large number of plates at a time and multiple Ultrasonic Test (UT) probes.

3.4 High Voltage Power supply

The High Voltage Power Supply Systems (HVPS) that provide the Megawatt level power to the ICRF [18][19], EC and DNB systems have been manufactured on the basis of technology that has been developed in house in the parent organization of the Indian DA. The HVPS are Pulse Step Modulation (PSM) based, where multi secondary transformers provide required power with isolation between each series connected Switch Power Supply (SPS) module. The modules are actively cooled and ratings of module is application based. A series of SPS modules using PSM technique provides the high voltage, Number of fibre optic links establishes the communication between the SPS modules and the HVPS controller, which is implemented on a FPGA based controller that provides voltage control and fast protections. Other safety and field interlocks are implemented on a PLC based slow controller. The HVPS have been tested on the ICRF loads, as a part of the demonstration of 1.5 MW power delivery from the Diacrode and Tetrode. Tests have been carried out on resistive loads and for low energy dump <10 Joules, prior to its integration. The operational integration of the HVPS is carried out by single team of engineers from the manufacturer and the DA, which is the repository of the knowledge for system integration.

A large fraction of the HVPS for the RF systems and the DNB system have been manufactured and ready for integration with functional load. An HVPS for the SPIDER accelerator is operational at the NBTF facility in Padova.

3.5 Summary of R & D- carried out with industries on Manufacturing Technologies

The special developments that have been carried out in the industry to meet the requirements, presented above establishes that industries have acquired developed the process, applied the necessary procedures and have established compliance with the codes, standards and quality requirements of manufacturing for fusion devices. The efforts invested in the industry have led to the creation of trained human resource, whose competence can be utilized in the missions for complex manufacturing, relevant to fusion.

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4. RISK ASSESSMENT AND MITIGATIONS

Assessment of risk in the realization of the deliverables for ensuring their objective application in integration with ITER is an essential part of the project planning for ITER. Important project level decisions have emerged out of the quantitative evaluation of risks. Investments in R&D set up presented in the earlier section - for the ICRF, EC, DNB, CDCCL; allocation of parallel fabrication contract for components in the status of ‘first of its kind’ – for the ICRF source, Cold Circulators for cryodistribution; incorporation of prototype scaled/ full scale as a pre manufacturing activity before the main production commences – for the cryostat and DNB; are decisions, that have been taken on the basis of risk assessment. These have to a substantial extent, mitigated the risk towards realisation of deliverables. However, the process of concurrent design activities that progresses with the manufacturing leads to a risk of change in the requirement and impacts the project schedule, irrespective of the status of mitigation of cost risks. Risk of schedule also arises in the situations where the construction plan is not adequately detailed, to ensure construction activity, post delivery. Delays in propagation and decisions on non-conformities is another category, where schedule risk have been evidenced.

A strong coordination amongst the stake holders in the form of an ITER Organization (IO)-Domestic Agency (DA) integrated working group, monitors the timely assessment of risks and their mitigation. Additionally, project teams with special authorizations have been set-up for specific procurements that have multiple DA interfaces in the procurement. Consolidation of interfaces and agreement amongst the stake holders for their respective areas of responsibility, as a mitigation measure, is an important outcome of the project teams.

The risk register is reviewed on a periodic basis and management level intervention is initiated for mitigation decisions, based on the understanding of possible impact of the risks. High rated Risks and issues have been addressed at the appropriate levels and mitigation actions were implemented accordingly to close those risks.

The dynamic process of risk evaluation and implementation of mitigation measures was evidence in the management of manufacturing for the Cooling Water System (CWS) pipe spools. The delivery under the CWS include ~4500 pipe spools upto diameter of 2m, in varying lengths and piping geometries, having ~ 18 km of piping and ~ 105 inch diameter of welding. The acceptance protocol for the spools have application of pressure as the confirmation of compatibility and ~ 20% of the fabrication is to be otherwise checked for weld and dimensional inspection in accordance with QC-2 requirements. An emerging risk in the possible defects in the weldments getting unnoticed at production, but posing as a non conformity at the construction site, during integration, was assessed. The mitigation plan incorporated a 100% quality check including volumetric examination, though not warranted as per quality classification, led to a full mitigation of the risk, beyond the initial part of the supplies.

5. SUMMARY

An overview of the development in the Indian DA in the perspective of ITER deliverables have been presented. Challenges in physics and engineering have been addressed in the laboratory form of dedicated test facilities, that have provided important results for the construction of ITER, as in the IC, Diagnostics and Cryogenic systems. A significant contribution from the industry has been effective in establishing technologies, many of which are for the first time, as in the case of accelerator grid for DNB, the cold circulators, the fabrication of cryostat.

While delivery of component from IN-DA continues as per the agreed schedule with IO, an assessment of risk is carried out as a dynamic process and mitigation actions are appropriately implemented, in consultation with IO.

Experience and knowledge that has been gathered in the process of establishing the requirements for ITER deliveries, leads to the creation of HR, specialized in undertaking challenges for larger engagements in the domestic program.

ACKNOWLEDGEMENT

The authors would like to place their sincere acknowledgement to the staff of ITER-India, whose efforts have led to success in several areas. Contribution of industrial partners, domestic and global are also sincerely acknowledged.

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