International Fusion Materials Irradiation Facility

The International Fusion Materials Irradiation Facility, also known as IFMIF, is a projected material testing facility in which candidate materials for the use in an energy producing fusion reactor can be fully qualified. IFMIF will be an accelerator-driven neutron source producing a high intensity fast neutron flux with a spectrum similar to that expected at the first wall of a fusion reactor using a deuterium-lithium nuclear reaction. The IFMIF project was started in 1994 as an international scientific research program, carried out by Japan, the European Union, the United States, and Russia, and managed by the International Energy Agency. Since 2007, it has been pursued by Japan and the European Union under the Broader Approach Agreement in the field of fusion energy research, through the IFMIF/EVEDA project, which conducts engineering validation and engineering design activities for IFMIF. The construction of IFMIF is recommended in the European Roadmap for Research Infrastructures Report, which was published by the European Strategy Forum on Research Infrastructures (ESFRI). The International Fusion Materials Irradiation Facility, also known as IFMIF, is a projected material testing facility in which candidate materials for the use in an energy producing fusion reactor can be fully qualified. IFMIF will be an accelerator-driven neutron source producing a high intensity fast neutron flux with a spectrum similar to that expected at the first wall of a fusion reactor using a deuterium-lithium nuclear reaction. The IFMIF project was started in 1994 as an international scientific research program, carried out by Japan, the European Union, the United States, and Russia, and managed by the International Energy Agency. Since 2007, it has been pursued by Japan and the European Union under the Broader Approach Agreement in the field of fusion energy research, through the IFMIF/EVEDA project, which conducts engineering validation and engineering design activities for IFMIF. The construction of IFMIF is recommended in the European Roadmap for Research Infrastructures Report, which was published by the European Strategy Forum on Research Infrastructures (ESFRI). The deuterium-tritium fusion reaction generates mono-energetic neutrons with an energy of 14.1 MeV. In fusion power plants, neutrons will be present at fluxes in the order of 1018 m−2s−1 and will interact with the material structures of the reactor by which their spectrum will be broadened and softened. A fusion relevant neutron source is an indispensable step towards the successful development of fusion energy. Safe design, construction and licensing of a fusion power facility by the corresponding Nuclear Regulatory agency will require data on the plasma-facing materials degradation under neutron irradiation during the life-time of a fusion reactor. The main source of materials degradation is structural damage which is typically quantified in terms of displacements per atom (dpa). Whereas in the currently constructed large fusion experiment, ITER, structural damage in the reactor steels will not exceed 2 dpa at the end of its operational life, damage creation in a fusion power plant is expected to amount to 15 dpa per year of operation. None of the commonly available neutron sources are adequate for fusion materials testing for various reasons. The accumulation of gas in the material microstructure is intimately related to the energy of the colliding neutrons. Due to the sensitivity of materials to the specificities in the irradiation conditions, such as the α-particle generation/dpa ratio at damage levels above 15 dpa per year of operation under temperature controlled conditions, material tests require the neutron source to be comparable to a fusion reactor environment. In steels, the 54Fe(n,α)51Cr and 54Fe(n,p)54Mn reactions are responsible for most of the protons and α-particles produced, and these have an incident neutron energy threshold at 0.9 MeV and 2.9 MeV respectively. Therefore, conventional fast fission reactors, which produce neutrons with an average energy around 1-2 MeV, cannot adequately match the testing requirements for fusion materials. In fact the leading factor for embrittlement, the generation of α-particles by transmutation, is far from realistic conditions (actually around 0.3 appm He/dpa). Spallation neutron sources provide a wide spectrum of energies up to the order of hundreds of MeV leading to potentially different defect structures, and generating light transmuted nuclei that intrinsically affect the targeted properties of the alloy. Ion implantation facilities offer insufficient irradiation volume (maximum values of a few hundreds µm layer thickness) for standardized mechanical property tests. Also the low elastic scattering cross section for light ions makes damage levels above 10 dpa impractical. In 1947, Robert Serber demonstrated theoretically the possibility of producing high energy neutrons by a process in which high energy deuterons are stripped off their proton when hitting a target, while the neutron continues on its way. In the 1970s, the first designs for high energy neutron sources using this stripping reaction were developed in the USA. In the 1980s, the rapid advances in high-current linear accelerator technology led to the design of several accelerator-driven neutron sources for satisfying the requirements of a high-flux high-volume international fusion materials testing facility. The Fusion Materials Irradiation Test (FMIT) facility based on a deuterium-lithium neutron source was proposed for fusion materials and technology testing. The deuterium-lithium reaction exploited for IFMIF is able to provide an adequate fusion neutron spectrum as shown by the comparison of IFMIF with other available neutron sources. In an experiment with 40 MeV deuterons from a cyclotron impinging on lithium, the neutron spectrum and the radioactivity production in the lithium were measured, and sufficient agreement with calculated estimates was found. IFMIF will consists of five major systems: an accelerator facility, a Li target facility, a test facility, a post-irradiation examination (PIE) facility and a conventional facility. The whole plant must comply with international nuclear facility regulations. The energy of the beam (40 MeV) and the current of the parallel accelerators (2 x 125 mA) have been tuned to maximize the neutron flux (1018 m−2 s−1) while creating irradiation conditions comparable to those in the first wall of a fusion reactor. Damage rates higher than 20 dpa per year of operation could be reached in a volume of 0.5 l of its High Flux Test Module that can accommodate around 1000 small test specimens. The small specimen testing techniques developed aim at full mechanical characterization (fatigue, fracture toughness, crack growth rate, creep and tensile stress) of candidate materials, and allow, besides a scientific understanding of fusion neutron induced degradation phenomena, the creation of the major elements of a fusion materials database suited for designing, licensing and reliably operating future fusion reactors. The main expected contributions of IFMIF to the nuclear fusion community are to: The engineering design of the IFMIF plant is intimately linked with the validation activities and was conducted during the first phase of the so-called IFMIF Engineering Validation and Engineering Design Activities project (IFMIF/EVEDA). The IFMIF Intermediate Engineering Design Report was established in June 2013 and adopted by the stakeholders in December 2013. The IFMIF Intermediate Engineering Design defines the major systems in outline. The two accelerator CW deuteron beams of 5 MW each impinge in an overlapping manner at an angle of ±9° with a footprint of 200 mm x 50 mm and a steady time profile on the liquid Li jet, with the Bragg peak absorption region at about 20 mm depth.