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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. [1] [2] 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). [3]
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.[ citation needed ] A fusion relevant neutron source is an indispensable step towards the successful development of fusion energy. [4] 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). [5] 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. [6]
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. [7] [8] 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). [9] 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. [10]
In 1947, Robert Serber demonstrated theoretically the possibility of producing high energy neutrons by a process in which high energy deuterons are stripped of their proton when hitting a target, while the neutron continues on its way. [11] In the 1970s, the first designs for high energy neutron sources using this stripping reaction were developed in the USA. [12] [13] 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. [14] [15] The Fusion Materials Irradiation Test (FMIT) facility based on a deuterium-lithium neutron source was proposed for fusion materials and technology testing. [16] [17] [18] [19]
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. [20] [21] [22] [23] 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. [24]
IFMIF will consist of five major systems: an accelerator facility, a Li target facility, a test facility, a post-irradiation examination (PIE) facility and a conventional facility. [25] [26] [27] 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. [28] 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: [29]
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 [26] 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.
The target facility, which holds the inventory of about 10 m3 of Li, forms and conditions the beam target. The Li screen fulfills two main functions: to react with the deuterons to generate a stable neutron flux in the forward direction and to dissipate the beam power in a continuous manner. The flowing Li (15 m/s; 250 °C) is shaped and accelerated in the proximity of the beam interaction region by a two-stage reducer nozzle forming a concave jet of 25 mm thickness with a minimum radius of curvature of 250 mm in the beam footprint area. The resulting centrifugal pressure raises the boiling point of the flowing Li and thus ensures a stable liquid phase. The beam power absorbed by the Li is evacuated by the heat removal system and the lithium is cooled to 250 °C by a serial of heat exchangers. The control of impurities, essential for the quality of the liquid screen, will be done through a tailored design of cold and hot trap systems, and purities of Li during operation better than 99.9% are expected. On-line monitoring of impurities will detect impurity levels over 50 ppm. Based on numerical analyses carried out in the last three decades, the beam-target interaction is not expected to have a critical impact on jet stability. [30]
The Test Facility will provide high, medium and low flux regions ranging from ›20 dpa/full power year (fpy) to ‹1 dpa /fpy with increasingly available irradiating volumes of 0.5 L, 6 L and 8 L that will house different metallic and non-metallic materials potentially subjected to the different irradiation levels in a power plant. More specifically, in the high flux region, fluences of 50 dpa in ‹3.5 years in a region of 0.5 L, together with power plant relevant fluences of ›120 dpa in ‹5 years in a region of 0.2 L, are planned. The high flux region will accommodate about 1000 small specimens assembled in 12 individual capsules independently temperature controlled that will allow not only mechanical characterization of the candidate structural materials tested, but also an understanding of the influence in their degradation with material temperature during irradiation.
The Post-Irradiation Examination facility, an essential part of IFMIF, is hosted in a wing of the main building in order to minimize the handling operations of irradiated specimens. [31] It will not only allow testing irradiated specimens out of the different testing modules, but also characterizing metallographically the specimens after destructive testing.
To minimise the risks in constructing IFMIF, the IFMIF/EVEDA project has constructed or is constructing prototypes of those systems which face the main technological challenges that have been identified throughout the years of international cooperation in establishing a fusion relevant neutron source, [17] [32] namely 1) the Accelerator Facility, 2) the Target Facility, and 3) the Test Facility. [33] [34] An Accelerator Prototype (LIPAc), designed and constructed mainly in European laboratories CEA, CIEMAT, INFN and SCK•CEN under the coordination of F4E and under installation at Rokkasho at JAEA premises, is identical to the IFMIF accelerator design up to its first superconductive accelerating stage (9 MeV energy, 125 mA of D+ in Continuous Wave (CW) current), and will become operational in June 2017. [35] A Li Test Loop (ELTL) at the Oarai premises of JAEA, integrating all elements of the IFMIF Li target facility, was commissioned in February 2011, [36] and is complemented by corrosion experiments performed at a Li loop (Lifus6) in ENEA, Brasimone. [37] A High Flux Test Module (two different designs accommodating either Reduced Activation Ferritic-Martensitic steels (RAFM) or SiC), [38] [39] [40] with a prototype of the capsules housing the small specimens were irradiated in the BR2 research reactor of SCK•CEN [41] and tested in the cooling helium loop HELOKA of the Karlsruhe Institute of Technology, Karlsruhe, [42] together with a Creep Fatigue Test Module [43] manufactured and tested at full scale at the Paul Scherrer Institute. Detailed specific information on the ongoing validation activities is being made available in related publications. [44] [45] [46] [47] [48] [49] [50]
The neutron is a subatomic particle, symbol
n
or
n0
, which has a neutral charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behave similarly within the nucleus, they are both referred to as nucleons. Nucleons have a mass of approximately one atomic mass unit, or dalton. Their properties and interactions are described by nuclear physics. Protons and neutrons are not elementary particles; each is composed of three quarks.
Fusion power is a proposed form of power generation that would generate electricity by using heat from nuclear fusion reactions. In a fusion process, two lighter atomic nuclei combine to form a heavier nucleus, while releasing energy. Devices designed to harness this energy are known as fusion reactors. Research into fusion reactors began in the 1940s, but as of 2024, no device has reached net power, although net positive reactions have been achieved.
A neutron source is any device that emits neutrons, irrespective of the mechanism used to produce the neutrons. Neutron sources are used in physics, engineering, medicine, nuclear weapons, petroleum exploration, biology, chemistry, and nuclear power. Neutron source variables include the energy of the neutrons emitted by the source, the rate of neutrons emitted by the source, the size of the source, the cost of owning and maintaining the source, and government regulations related to the source.
ITER is an international nuclear fusion research and engineering megaproject aimed at creating energy through a fusion process similar to that of the Sun. Upon completion of construction of the main reactor and first plasma, planned for late 2025, it will be the world's largest magnetic confinement plasma physics experiment and the largest experimental tokamak nuclear fusion reactor. It is being built next to the Cadarache facility in southern France. ITER will be the largest of more than 100 fusion reactors built since the 1950s, with ten times the plasma volume of any other tokamak operating today.
Neutron radiation is a form of ionizing radiation that presents as free neutrons. Typical phenomena are nuclear fission or nuclear fusion causing the release of free neutrons, which then react with nuclei of other atoms to form new nuclides—which, in turn, may trigger further neutron radiation. Free neutrons are unstable, decaying into a proton, an electron, plus an electron antineutrino. Free neutrons have a mean lifetime of 887 seconds.
Neutron generators are neutron source devices which contain compact linear particle accelerators and that produce neutrons by fusing isotopes of hydrogen together. The fusion reactions take place in these devices by accelerating either deuterium, tritium, or a mixture of these two isotopes into a metal hydride target which also contains deuterium, tritium or a mixture of these isotopes. Fusion of deuterium atoms results in the formation of a helium-3 ion and a neutron with a kinetic energy of approximately 2.5 MeV. Fusion of a deuterium and a tritium atom results in the formation of a helium-4 ion and a neutron with a kinetic energy of approximately 14.1 MeV. Neutron generators have applications in medicine, security, and materials analysis.
In nuclear physics, an energy amplifier is a novel type of nuclear power reactor, a subcritical reactor, in which an energetic particle beam is used to stimulate a reaction, which in turn releases enough energy to power the particle accelerator and leave an energy profit for power generation. The concept has more recently been referred to as an accelerator-driven system (ADS) or accelerator-driven sub-critical reactor.
DEMO, or a demonstration power plant, refers to a proposed class of nuclear fusion experimental reactors that are intended to demonstrate the net production of electric power from nuclear fusion. Most of the ITER partners have plans for their own DEMO-class reactors. With the possible exception of the EU and Japan, there are no plans for international collaboration as there was with ITER.
The High Flux Isotope Reactor (HFIR) is a nuclear research reactor at Oak Ridge National Laboratory (ORNL) in Oak Ridge, Tennessee, United States. Operating at 85 MW, HFIR is one of the highest flux reactor-based sources of neutrons for condensed matter physics research in the United States, and it has one of the highest steady-state neutron fluxes of any research reactor in the world. The thermal and cold neutrons produced by HFIR are used to study physics, chemistry, materials science, engineering, and biology. The intense neutron flux, constant power density, and constant-length fuel cycles are used by more than 500 researchers each year for neutron scattering research into the fundamental properties of condensed matter. HFIR has about 600 users each year for both scattering and in-core research.
Radiation damage is the effect of ionizing radiation on physical objects including non-living structural materials. It can be either detrimental or beneficial for materials.
Lithium titanates are chemical compounds of lithium, titanium and oxygen. They are mixed oxides and belong to the titanates. The most important lithium titanates are:
Radiation materials science is a subfield of materials science which studies the interaction of radiation with matter: a broad subject covering many forms of irradiation and of matter.
The Materials Testing Reactor (MTR) was an early nuclear reactor specifically designed to facilitate the conception and the design of future reactors. It produced much of the foundational irradiation data that underlies the nuclear power industry. It operated in Idaho at the National Reactor Testing Station from 1952 to 1970.
The Soreq Applied Research Accelerator Facility (SARAF), located at the Soreq Nuclear Research Center (SNRC) in Yavne, Israel, is a multi-user and versatile particle accelerator facility based on a proton/deuteron RF superconducting linear accelerator. It has a variable energy of around 40 MeV and a continuous wave (CW) high ion current.
In nuclear fusion power research, the plasma-facing material (PFM) is any material used to construct the plasma-facing components (PFC), those components exposed to the plasma within which nuclear fusion occurs, and particularly the material used for the lining the first wall or divertor region of the reactor vessel.
The ARC fusion reactor is a design for a compact fusion reactor developed by the Massachusetts Institute of Technology (MIT) Plasma Science and Fusion Center (PSFC). ARC aims to achieve an engineering breakeven of three. The key technical innovation is to use high-temperature superconducting magnets in place of ITER's low-temperature superconducting magnets. The proposed device would be about half the diameter of the ITER reactor and cheaper to build.
The MIAMI facility is a scientific laboratory located within the Ion Beam Centre at the University of Huddersfield. This facility is dedicated to the study of the interaction of ion beams with matter. The facilities combine ion accelerators in situ with Transmission Electron Microscopes (TEM): a technique that allows real-time monitoring of the effects of radiation damage on the microstructures of a wide variety of materials. Currently the laboratory operates two such systems MIAMI-1 and MIAMI-2 that are the only facilities of this type in the United Kingdom, with only a few other such systems in the world. The MIAMI facility is also part of the UKNIBC along with the Universities of Surrey and Manchester, which provides a single point of access to a wide range of accelerators and techniques.
The China Fusion Engineering Test Reactor, or CFETR, is a proposed tokamak fusion reactor, which uses a magnetic field in order to confine plasma and generate energy. As of 2015, tokamak devices are leading candidates for the construction of a viable and practical thermonuclear fusion reactor. These reactors may be used to generate sustainable energy whilst ensuring a low environmental impact and a smaller carbon footprint than fossil fuel-based power plants.
The tritium breeding blanket, is a key part of many proposed fusion reactor designs. It serves several purposes; primarily it is to produce further tritium fuel for the nuclear fusion reaction, which owing to the scarcity of tritium would not be available in sufficient quantities, through the reaction of neutrons with lithium in the blanket. The blanket may also act as a cooling mechanism, absorbing the energy from the neutrons produced by the reaction between deuterium and tritium ("D-T"), and further serves as shielding, preventing the high-energy neutrons from escaping to the area outside the reactor and protecting the more radiation-susceptible portions, such as ohmic or superconducting magnets, from damage.
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