by Chuck Flanagan, TAC secretary 1992-1998

January 24, 2005

Introduction

The Technical Advisory Committee (TAC) provided technical advice to the ITER Council and to the Project during the six years of the formal Engineering Design Activities of ITER, from 1992 through 1998, and during the the three-year EDA extension, from 1998 to 2001.

The TAC consisted of four members from each of the four Parties, for a total of 16 members, including the Chair, plus a Committee secretary. The members were selected to assure that all requisite areas of technical expertise were represented. Each Committee member acted in an individual capacity and provided his technical expertise as appropriate on all matters addressed by the Committee. Typically. most Committee members were able to attend most meetings so good continuity of involvement was maintained. Over the years, some members of the Committee were changed. And in 1998, all members from the Unites States left the Committee, including the Chair and the secretary, when the United States withdrew from ITER. The Japanese delegation provided the new Chair and secretary.

The Committee meetings followed a similar format. At each meeting, the Director with members of his staff, and sometimes with additional experts, made formal presentations to the TAC on the subjects being reviewed. This usually lasted one-to-two days. Following the formal presentations, the TAC reviewed and discussed the material presented and drafted minutes and a report of the meeting, including findings and recommendations. The draft report, findings and recommendations were reviewed with the Director and his staff. TAC members, prior to the close of the meeting, agreed to the draft minutes and report. The final report was issued after incorporating review comments by the committee members. The Chair presented the results of each TAC meeting to the Council at a meeting that generally followed soon after the TAC meeting. After acceptance of the TAC report by the Council, the Director and the Project acted upon the TAC findings and recommendations.

The original duration of the EDA was six years starting in July 1992. In 1998 the Parties agreed  to extend it by three years.

At the beginning of the EDA, the Director and the Project had available to them the output from the three-year ITER Conceptual Design Activities (CDA) that ended in December 1990, and that output formed the basis of the initial Project considerations about the ITER design. The ITER design naturally evolved during the EDA, and the Director and the Project presented the status of the design to the TAC throughout that period. Starting from a Preliminary Design concept, the design stages were an Outline Design, an Interim Design, a Detailed Design, and the Final Design. Naturally, the design matured through the various stages, and the detail associated with each system and subsystem of the design became more and more defined. During the initial six-year EDA period, the TAC met several times each year to review and discuss the status of the design of ITER as it progressed, along with associated support programs. The material reviewed by the TAC at each meeting was focused on the current key issues and concerns as the ITER design evolved and was developed. The subjects addressed at each meeting were suggested or requested by the ITER Council, or were developed by the TAC Chair in discussions with the Director. 

The first meeting of the TAC was held on 11-13, November 1992, at the San Diego ITER Co-center. This was primarily an organizational meeting at which the TAC adopted its rules of procedure and they were approved by the ITER Council.

Preliminary ITER Design

The TAC conducted a review of the Preliminary ITER design. The review addressed the overall design concept, the machine parameters and physics basis, the primary structural, first-wall and high-heat-flux materials and coolants, the major engineering systems, especially the magnets, and the overall preliminary cost estimate. One of the major TAC recommendations from this meeting was that if the total cost of ITER were to become significantly larger than the ITER cost projected in the CDA, a lower-cost machine, involving reduced margin for meeting the objectives, should be considered by the Director and the Joint Central Team.

At the following TAC meeting, there was continued concern that the size of the device was large, as was the associated power level. Because of concerns about the size, and the associated cost, the TAC recommended that the size should not exceed a plasmamajor radius of 7.75 m. The TAC also recommended that the Director should be prepared to diminish still further the machine size parameters in order to keep the cost below the ceiling recommended by the Council and should indicate the consequences on the expected plasma performance.

Outline Design

The Project evolved ITER to an Outline Design that was then reviewed by the TAC along with the critical elements of the ITER Work Programme so as to confirm that the proposed R&D supported the design. The following elements of the program were reviewed and detailed findings and recommendations provided to the Project.

• Magnets,
• Vacuum Vessel,
• First-Wall, Shield-Blanket,
• Divertor,
• Heating and Current Drive,
• Remote Handling,
• Tritium Plant,
• Safety-Related R&D and Design Standards and Codes

After the TAC review of the Outline Design and associated cost estimates in early 1994, the findings and recommendations from TAC led to the performance of a number of sensitivity analysis by the Director and Joint Central Team. The objective of those analyses was to determine an optimum way to achieve a reduction in the estimated construction cost of ITER and minimize the impact on the performance margin of the design. The sensitivity study began with the Outline Design as the reference point. Alternate design points were identified and studied, including cases in which the plasma major radius was reduced by up to about 10%, and cases in which the plasma elongation was increased up to the limits set by a single-null divertor configuration and by the ability to control the plasma vertical position without internal coils. Variations of up to about 10% were allowed in other parameters, such as the q-value, aspect ratio, toroidal field strength and plasma current. The alternate design points considered were all to lie within the constraints imposed by the magnet design concept and magnet structural approach. The number of toroidal field coils was varied in the range 20-24.

The TAC found that the Outline Design was successful in its attempt to maximize physics and engineering performance while minimizing cost and complexity. However, the TAC noted that the uncertainties in the models used to project plasma performance exceeded  the differences in performance projected for the various alternate design points considered in the sensitivity study and for this reason it might be possible to realize additional small reductions (<10%) in the cost. The TAC considered that it would be prudent to retain the present major machine parameters of the Outline Design. As to a possible change in the number of TF coils from 24 to 20, the TAC found that the choice of 24 coils appeared appropriate.

Following that review, the Project continued a program to evolve the design. An informal TAC review was conducted to examine the evolution of the design. In particular, the review emphasized those areas where the most significant departures from the Outline Design were under consideration. Those areas were the magnet system (including mechanical structures, magnet assembly, poloidal field system and plasma control), the shield/blanket, the divertor and plasma-facing components, operational requirements and tritium supply, and safety.

Interim Design

As the Interim ITER Design evolved, the TAC conducted an informal in-depth review, in Garching, of all the In-Vessel Systems and associated physics, followed by a similar in-depth review, in Naka, of all the Ex-Vessel Systems and associated physics.

Those reviews were followed shortly afterward by a review of the total Interim ITER Design and associated cost estimate. That was a key review in the evolution of the ITER design. At that review, the TAC recognized that excellent progress had been made in all aspects of the design of ITER.

The TAC concluded that the Interim Design could fully meet the ITER programmatic mission and technical objectives including demonstrating controlled ignition and extended burn, with steady-state as an ultimate goal, demonstrating technologies essential to a reactor in an integrated system, and performing integrated testing of high-heat-flux and nuclear components. The TAC also concluded that the ITER parameters and engineering design approaches were well suited to meet the mission and technical objectives.

The TAC made detailed conclusions regarding various aspects of the Project status and the Interim Design:

• that the Interim Design was sufficient to define the R&D to be carried out during the balance of the EDA and that the R&D was expected to confirm the technical validity of the design and, in many cases, would also identify optimum and cost-effective manufacturing techniques; it was TAC's view that it was essential that this R&D program be fully implemented;
• regarding plasma performance, that the design had sufficient margin to meet the requirements for ignition and 1,000-second burn; the provision of 100 MW of auxiliary power greatly increased confidence in plasma performance so that, even with conservative assumptions, sustained driven-burn at 1.5 GW fusion power was essentially assured;
• regarding tokamak engineering systems, considering both in-vessel and ex-vessel components and related physics, that the engineering designs had now progressed to the point to confirm that the ITER requirements could be met using the Interim Design approach and that reliable cost estimates could be provided;
• regarding the tokamak support systems, including the site plan and buildings, that the designs of these systems had progressed beyond the conceptual stage and, in many cases, had reached the point at which engineering requirements could be specified and adequate cost estimates made;
• that safety requirements had been prepared and documented which, with the planned design approaches, will ensure safe operation of the ITER facility; 
• that the cost estimating process conducted by the JCT was sound and that the cost estimate provided was valid; the estimate was sufficiently complete and detailed, at the present stage, to provide a reliable total cost.

During the EDA, the Project implemented a comprehensive Research and Development (R&D) program that was conducted in parallel with the ongoing design efforts. Once the total design and associated cost estimate were reviewed, the TAC efforts focused on a technical review of the R&D activities and plans. This included an overview of the R&D efforts and their sharing between the Parties, and an overview of the Work Breakdown Structure items. The review also addressed the plans and status of the "large-seven" R&D projects, which were:

1. Central Solenoid (CS) Model Coil Project;
2. Toroidal Field (TF) Model Coil Project;
3. Vacuum Vessel Sector Project;
4. Blanket Module Project;
5. Divertor Cassette Project;
6. Blanket Module Remote Handling Project;
7.  Divertor Module Remote Handling Project.

In mid-1996, the TAC performed an informal assessment of those aspects of the ITER design where important improvements were introduced by the Director following the Interim Design Review. That was followed by an informal assessment of the safety of ITER, held at the tail end of a two-week safety review by safety experts and the JCT. The TAC-related meeting was a joint meeting of TAC and the JCT. A second informal review was held to assess the draft physics chapter for the Detailed Design Report. The informal physics review was held after the 16th IAEA Fusion Energy Conference in Montreal and was held in collaboration with the ITER Physics Committee.

Detailed Design

In late 1996, the TAC reviewed the technical basis for the ITER Detailed Design Report (DDR) that was prepared by the Director and the JCT. With regard to engineering systems, the TAC noted that approval of the Interim Design Report by the ITER Council in late-1995 had allowed the main features of the ITER design to be frozen and the detailed design of individual components and the associated issues of design integration to be addressed. It was evident from the technical documentation for the DDR that, for most components, the ITER design had progressed to the level of detailed subsystem design and design integration, including incorporation of integrated safety and remote handling requirements. Considerable attention was given to the tokamak building, so as to assure that safety and remote handling requirements would be met, that service lines would be incorporated in an efficient and functionally acceptable manner to result in a well-designed site layout, and that a range of seismic requirements could be satisfied. The design was evolved in strict observance of a design policy of maintaining the total cost within the cost estimate range developed at the Interim Design Report.

With regard to the physics basis for ITER, the TAC noted that there was an international worldwide physics effort in support of ITER, encompassing seven Physics Expert Groups and involving many ITER-specific studies in the experimental and theoretical programs of the Parties. The new experimental results, in general terms, confirmed and strengthened the physics basis for the ITER design. Remaining open issues were being resolved by focused experimental effort in the tokamak programs of the Parties. The TAC also noted the encouraging worldwide progress in the development of physics-based transport models for tokamaks and endorsed the ongoing effort by the JCT and the Physics Expert Groups to include such models in projections of plasma performance in ITER. The TAC’s overall assessment of the physics basis for ITER was that the design parameters had been well chosen for meeting ITER’s technical objectives.

Regarding the ITER cost, the TAC noted that essentially no change had occurred in the overall cost estimate presented in the Interim Design and Cost Review in 1995.

Subsequently, the Director and the Project focused on producing the Final ITER Design and associated documentation. During this period, the TAC again conducted a review of the ITER R&D program and the diagnostics and the associated control system.

As the result of that review, the TAC's general assessment was that there were major and important achievements in the R&D program and that the overall progress was impressive. In particular, the large-seven projects retained almost their full initial scope, and many of them were on-schedule for the completion of this scope within the time-period of the original EDA. The TAC noted that a few of the major milestones of the R&D program would be delayed. In particular, although the industrial manufacture of the two Central Solenoid Coil Modules would still be completed during the EDA, the cool down of the Central Solenoid Model Coil would occur just after the EDA, and the cool down of the Toroidal Field Model Coil would not occur until somewhat later.

The TAC also noted that the main test facilities built or modified as part of the ITER R&D program would continue to be exploited after the EDA program was completed, so as to provide further essential and validating information, for example on the performance of components over many cycles, to test the margins available for some systems above the specified requirements, to provide for additional tests of interfaces between different components, and to define remote maintenance procedures.

Regarding the first review of the diagnostics systems and controls, the TAC noted that excellent progress had been made in defining and designing the diagnostics equipment to meet the ITER requirements both for plasma control and for those measurements needed to satisfy the goals of the scientific program. The principal aim of the diagnostics studies to that date had been to define the diagnostics and to perform sufficient engineering design to ensure that there was adequate access and that the diagnostics were compatible with the other ITER components. While much of the preliminary engineering work had been done, some areas still needed attention in the near term. The TAC also noted that most of the needed diagnostics for ITER were already in use. Nevertheless those diagnostics could require R&D to adapt them to ITER. In addition, there were newer or proposed diagnostics (some speculative) which could need substantial R&D.

Final Design

By January 1998, the Director and the Project had completed the technical documentation for the Final Design Report and the TAC met with the Director and the Project staff and performed a detailed review of the Final Design.

The TAC noted that the purpose of the ITER Engineering Design Activities (EDA) was to produce a detailed, complete, and fully integrated engineering design of ITER and all technical data necessary for future decisions on the construction of ITER. In the TAC’s view, the work that was carried out during the EDA and was nearing completion fulfilled that purpose.

In the TAC’s view, the ITER parameters and overall design of the Final Design Report were adequate to fulfill all of the ITER technical objectives.

The ITER design evolved from the Outline Design, through the Interim and Detailed Designs, to the Final Design, with successive improvements at each stage. As a result of those improvements, the TAC concluded that the Final Design provided a robust mechanical structure for the magnets and other components, efficient remote maintenance procedures, adequate plasma power and particle exhaust, and flexibility to accommodate a range of optimized plasma configurations.

The EDA included an R&D program aimed at confirming the design and establishing manufacturing methods for all major components. In the TAC’s view, the R&D results were sufficient to qualify the major design choices, but final confirmation required completion of the full committed EDA R&D program.

The ITER EDA served as a stimulant to the world tokamak program, focusing experimental and theoretical efforts on key issues of reactor tokamak physics. Confidence in the performance of the ITER plasma was increased, both by major advances in physics characterization and understanding and by appropriate modifications of the design, where necessary. In the TAC's view, the physics operating range at full performance in ITER was acceptable, although modest; the operating range would continue to broaden assuming sustained flow of relevant information from a strong world tokamak program.

In the TAC’s view, the demonstration of the safety and environmental potential of ITER was effectively achieved.

An objective of the EDA was to maintain the cost within an agreed range of the CDA cost estimate. The estimated construction cost of ITER was established through detailed and comprehensive costing of procurement-like packages by industries of all four Parties. The costs of operation and decommissioning were also estimated. In the TAC’s view, the estimated construction cost was valid, and it remained within the range agreed at the start of the EDA.

Finally, it was the TAC’s view that the ITER design and the accompanying technical data would be sufficient to allow a construction decision to be taken immediately after the (then) scheduled end of the EDA. 

Revised Technical Objectives and ITER-FEAT, a Reduced Cost ITER Design

In June 1998 the ITER technical objectives were revised to reduce costs and objectives while still maintaining the programmatic objective described in the EDA Agreement.

The revised technical objectives for ITER called for the device to achieve extended burn in an inductively driven plasma with the ratio of fusion power to auxiliary heating power of at least 10 for a range of operating scenarios, and with a duration sufficient to achieve stationary conditions on the time scales characteristic of plasma processes. ITER should aim at demonstrating steady-state operation using non-inductive current drive, with the ratio of fusion power to input power for current drive of at least 5. Finally, the possibility of controlled ignition should not be precluded. To satisfy the plasma performance requirements, an inductive pulse flat-top capability during burn of about 300s to 500s, under nominal operating conditions, should be provided. To limit the fatigue of components, operation should be limited to a few 10s of thousands of pulses. To demonstrate steady-state operation using non-inductive current drive in reactor-relevant regimes, the machine design should be able to support equilibria with high bootstrap current fraction and plasma heating dominated by fusion alpha particles. To carry out nuclear and high heat-flux component testing relevant to a future fusion reactor, the engineering requirements were:

The Director and the JCT, supported by the Home Teams, embarked on a series of design studies to develop options for ITER that would satisfy the revised technical objectives and would reduce the direct capital cost by about a factor of two below that of the ITER Final Design. The Project developed several options and then converged to a final design then designated as ITER-FEAT.

The TAC met twice in 1999. It reviewed the progress of the Project and the ITER-FEAT outline design. The TAC fully endorsed this design and noted the progress made in reducing physics uncertainties and in achieving a design that satisfied the revised technical objectives. The TAC noted that the ITER-FEAT outline design made significant reductions in the direct capital cost, but was at 56 per cent of the cost of the prior ITER Final Design. The TAC recommended that every effort be made to reduce the cost further to achieve the target of 50 per cent of that of the ITER Final Design without jeopardizing the feasibility and necessary engineering margins for ITER-FEAT.

During the remaining two years of the EDA extension, through July 2001, the Director and the JCT further developed the details of the major systems and subsystems of ITER-FEAT and updated the descriptions of the design and its associated support systems and subsystems with this objective. The TAC met twice more, in mid-2000 and early 2001, to review the interim and draft final reports of this work. At its last meeting the TAC concluded that the ITER-FEAT design was sufficiently mature for construction to begin.

The attached table is a summary of the TAC meetings indicating the date and place of each meeting, the material reviewed, and provides links to the reports.