EXECUTIVE SUMMARY

MISSION

Continued progress toward the development of a fusion power plant will require addressing a broad set of issues regarding environmental acceptability, safety, and economic viability. Among such issues, the development and qualification of radiation-resistant and low-activation materials will be a key factor. These low-activation materials must survive exposure to damage from neutrons having an energy spectrum peaked near 14 MeV with annual radiation doses in the range of 20 displacements per atom (dpa). To test and fully qualify candidate materials up to the expected doses of a fusion power reactor, a high flux source of high energy neutrons, presently not existing, has to be build and operated.

The test facility suitable for such purposes has been explored through a number of international studies and workshops over the last decade. Under the assumption that such a facility should be available early in the next century, a neutron source from the Deuterium-Lithium (D-Li) stripping reaction has been selected as the basic concept of the International Fusion Materials Irradiation Facility (IFMIF) [1,2,3,4]. The technology of the accelerator-based D-Li neutron source concept was first developed by the Fusion Materials Irradiation Test (FMIT) Project (1978-84) [5,6] and later by the Energy Selective Neutron Irradiation Test Facility (ESNIT) Program (1988-92) [7,8,9]. Major worldwide advances in accelerator technology over the past decade have further added to the credibility of this approach.

The mission of IFMIF is to provide an accelerator-based, D-Li neutron source to produce high energy neutrons at sufficient intensity and irradiation volume to test samples of candidate materials up to about a full lifetime of anticipated use in fusion energy reactors. IFMIF would also provide calibration and validation of data from fission reactor and other accelerator-based irradiation tests [10]. It would generate an engineering base of material-specific activation and radiological properties data, and support the analysis of materials for use in safety, maintenance, recycling, decommissioning, and waste disposal systems.

CONCEPTUAL DESIGN ACTIVITY

The objective of IFMIF Conceptual Design Activity (CDA) is to provide a reference design and a project basis, including a schedule and cost estimate, satisfying the mission and the requirements for a facility as described above. The CDA was carried out under the direction of a subcommittee of the International Energy Agency (IEA), Executive Committee on Fusion Materials [11]. A users group of materials scientists was organized by the Executive Committee, outside of the CDA envelope, to provide requirements, guidance and review of the design. The design team consisted of specialists in all technical areas relevant to IFMIF, working, most of the time in their home institutions in Europe, Japan, the United States and the Russian Federation. The work was coordinated by a technical leader, assisted by deputy leaders who were responsible for the major technical areas. The CDA was done over a 2-year period, 1995-96, through a series of technical meetings and workshops in which tasks were defined and discussed and then completed at the home institutions. After a joint technical preparation workshop held at FZK in Karlsruhe, Germany in September 1994 [12], specific area meetings were held during the spring and summer of 1995 in Europe (test facilities) [13], Japan (target systems) [14], and the United States (accelerator) [15,16]. The initial baseline design concept was developed during a 2-week design integration workshop, October 16 - 27, 1995, at Oak Ridge National Laboratory. The first draft of the CDA report was also produced during that workshop [17]. The second design integration workshop was held at the Japanese Atomic Energy Research Institute, Tokai, Japan, May 20-24, 1996 [18,19]. At this meeting, the baseline design was revised to reflect several changes discussed by the design team. The first draft of a cost estimate and schedule as well as a plan for the Engineering Validation Phase (EVP) was also produced. The third design integration meeting was held at the ENEA-Frascati Research Center, Italy, October 14-25, 1996. The final CDA report was prepared at this meeting and was published December 31, 1996 [20]. The entire CDA effort was accomplished with a professional work force of approximately 25 person years per year.

The Work Breakdown Structure (WBS) for the project has four major elements that defined the technical focus for the CDA as follows:

The schedule of meetings and activities for the CDA was as follows:

The IFMIF program relies on an international electronic network system for com-munication among the project groups of various countries and institutions. To set up an efficient communication system, protocols and software have been specified. The basic set includes: EUDORA for e-mail, Microsoft Word 6.0 for text format, Microsoft Excel 5.0 for spreadsheet format, and AUTOCAD 12 (.DWG) format for drawings. A computer server has been set up at ENEA-Frascati Research Center, Italy, where project documents (reports, drawings, etc.) released from project management are stored and easily accessible to all the project participants. An IFMIF home page may be accessed by Internet on the world-wide web (http://www.frascati.enea.it/ifmif/).

In addition to providing up-to-date design information for future activities, the common server could provide the design team with a data base of supporting information, such as technical reports and results of research and development programs for possible future phases of the IFMIF project. Large databases such as the files from FMIT and ESNIT could be transferred to this system.

DESIGN CONCEPT

USER REQUIREMENTS

The design concept for IFMIF is based on input from the materials community on the estimated test volume required to obtain useful irradiation data in a reasonably short operating time. Detailed design studies of the test assembly indicate that a test volume of about 0.5 L is required in a region producing a flux equivalent to 2 MW/m² (0.9 ´ 10¹⁸ n/m² s, uncollided flux) or greater. A fraction of this volume, about 0.1 L, is available at a flux equivalent to 5 MW/m² for accelerated testing.

Two accelerator systems combined will provide a continuous wave of 250 mA of deuterons at 32, 36, or 40 MeV. Neutronics calculations indicate that 40 MeV deuterons provide the maximum high-flux irradiation volume and provide a reasonable simulation of the fusion energy gaseous and solid transmutation rates in most metallic components. Some of the transmutation components in ceramic materials are best simulated with 32 or 36 MeV deuterons. The flexibility of choosing deuteron energies between 32 and 40 MeV during irradiation campaigns allows experiments designed to establish the influence of certain transmutation products to be conducted.

An estimate of the test volume and the corresponding displacement rate in a test assembly with iron-based specimens per year of facility operation is as follows:

Assuming a total facility availability of 70%, these displacement numbers which represent a full power year (fpy), have to be multiplied by a factor of 0.7.

A quasi-continuous operation is mandatory. Annealing times of point defects shorter than the repetition time of pulses and rate effects in the case of low duty-cycle sources would introduce unacceptable uncertainties in the observed radiation effects. It is planned that IFMIF will operate with two accelerators providing identical overlapping beam footprints on either one of two lithium targets. This configuration minimizes flux perturbations caused by a beam-off transient in one of the accelerators (i.e., the maximum likely temporal variation in the flux would be a factor of 2).

Because of the level of uncertainty in the amount of testing and development needed to characterize the damage effect of 14-MeV neutrons and to quantify materials for reactor lifetime service, the IFMIF facility has been designed from the outset to accommodate a possible future expansion in irradiation capacity and test volume. Two additional accelerators can be added so that two test assemblies could be irradiated simultaneously. The lithium system can be expanded so that both target systems can operate at the same time. At full-power operation, this expansion would double the test volume for the displacement rates as shown above. If needed, this additional volume would allow much more flexibility in the range of operating conditions within the test assemblies and thereby significantly reduce the time to characterize and test new material options.

OVERALL FACILITY LAYOUT

A three-dimensional view of the overall IFMIF facility is shown in Figure 1. The two parallel accelerators, each approximately 50 m long, produce a beam which is turned through approximately 90 degrees where it is directed to one of the targets where the two beams overlap. The accelerator systems along with the lithium loop and processing systems are located below ground level. Major power systems, access cells and hot cell facilities are located at ground level. The first floor level contains laboratories for the handling and testing of the irradiated components and specimens.

TEST FACILITIES

Three Vertical Test Assemblies (VTAs) are provided for a wide range in neutron flux. That is, test beds for instrumented and/or in situ experiments in metals and nonmetals can be provided for any loading regime from 50 dpa/y to 0.01 dpa/y. Detailed test matrixes have been defined for the high and medium flux regions, showing that on the basis of small specimen test technologies, a database for an engineering design of an advanced fusion reactor can be established for a variety of structural materials and ceramic breeders. Design concepts for VTAs with instrumented capsules for post irradiation and in-situ experiments using either NaK or helium gas as coolant have been developed together with the design concepts for remote handling and hot cell facilities with capacity for investigating all irradiation specimens on the IFMIF site.

The test cell (Figure 2) has an actively cooled steel liner and a removable shield plug with ports which allow flexible installation of two Vertical Test Assemblies (VTA1 and VTA2) for the high and medium flux regions, and a Vertical Irradiation Tube (VIT) system for the low and very low flux regions. The VTAs penetrate through the test cell ceiling and include the primary coolant, instrumentation and the test modules to be irradiated. This concept maintains a high degree of flexibility with respect to any future needs. In the present reference design the high flux region consists of either NaK cooled test modules for low and medium irradiation temperatures or helium gas cooled test modules for high temperature applications with the strong option to replace the NaK cooled version after the feasibility of the helium concept has been shown experimentally mainly by thermal hydraulics tests. Major advantages of helium gas instead of NaK are flexibility with respect to irradiation temperatures as well as safety and maintenance considerations (NaK has more than 10 times higher decay heat than Fe during the first day after irradiation). Either simultaneous in-situ push-pull creep fatigue tests on three individual specimens or in-situ tritium release tests on breeder materials are foreseen in the medium flux region. The VIT system in the low and very low flux region is presently dedicated to special purpose materials like ceramic insulators, rf windows, diagnostic materials or superconducting materials.

Major engineering efforts have been undertaken to completely remote control any maintenance and assembling/disassembling activities in the test cell, the access cell and the service cell during normal and off-normal operation scenarios. Once the specimens are retrieved from the capsules in the test module handling cell, they will be mechanically tested in the Post Irradiation Examination (PIE) hot cells followed by microstructural investigations like Scanning Electron Microscopy (SEM) or Transmission Electron Microscopy (TEM) in the glove box laboratory (Figure 3). Tritium containing or contaminated specimens will be analyzed in detail in the tritium laboratory. Any tritium exposure to personal or environment will be avoided by effective tritium retention systems.

Figure 3. Testing facilities.

 

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