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Materials for a fusion reactor first wall and blanket structure must be able to reliably function in an extreme environment that includes 10-15 MW-year/m2 neutron and heat fluences. The various materials and structural challenges are as difficult and important as achieving a burning plasma. Overcoming radiation damage degradation is the rate-controlling step in fusion materials development. Recent advances with oxide dispersion strengthened ferritic steels show promise in meeting reactor requirements, while multi-timescale atomistic simulations of defect-grain boundary interactions in model copper systems reveal surprising self-annealing phenomenon. While these results are promising, simultaneous evaluation of radiation effects displacement damage (≤ 200 dpa) and in-situ He generation (≤ 2000 appm) at prototypical reactor temperatures and chemical environments is still required. There is currently no experimental facility in the U.S. that can meet these requirements for macroscopic samples. The E.U. and U.S. fusion communities have recently concluded that a fusion-relevant, high-flux neutron source for accelerated characterization of the effects of radiation damage to materials is a top priority for the next decade. Data from this source will be needed to validate designs for the multi-$B next-generation fusion facilities such as the CTF, ETF, and DEMO, that are envisioned to follow ITER and NIF.
The Fusion Materials Irradiation Test Facility (FMIT) is a high-energy, high-flux neutron source for fusion materials development. The FMIT linear accelerator will produce a 35 MeV beam of deuterons that generates high-energy neutrons by a nuclear stripping reaction with flowing liquid lithium targets. The targets will be located in two identical irradiation test cells, either of which will provide an irradiation volume of 10 cm3 at a neutron flux of 1015 n/cm2-s and 500 cm3 at a flux of 1014 n/cm2-s. FMIT has been authorized by the US Congress and will be constructed and operated by the Hanford Engineering Development Laboratory (HEDL) at Richland, Washington, in collaboration with the Los Alamos Scientific Laboratory (LASL) which is providing the accelerator design. The project is currently entering the detailed design phase, targeting for start of construction in early 1980 and operaion in 1983-84. Research and development programs are underway at both HEDL and LASL to resolve uncertainties in the lithium target and accelerator designs.
The successful development of energy-conversion machines based upon nuclear fission or fusion reactors is critically dependent upon the behavior of the engineering materials used to construct the full containment and primary heat extraction systems. The development of radiation damage-resistant materials requires irradiation testing facilities which reproduce, as closely as possible, the thermal and neutronic environment expected in a power-producing reactor. The Oak Ridge National Laboratory (ORNL) reference core design for the Center for Neutron Research (CNR) reactor provides for instrumented facilities in regions of both hard and mixed neutron spectra, with substantially higher fluxes than are currently available. The benefits of these new facilities to the development of radiation damage resistant materials are discussed in terms of the major US fission and fusion reactor programs.
It is widely agreed that the development of materials for fusion systems requires a high flux, 14 MeV neutron source. The European Union, Japan, Russia and the US have initiated the conceptual design of such a facility. This activity, under the International Energy Agency (IEA) Fusion Materials Agreement, will develop the design for an accelerator-based D-Li system. The first organizational meeting was held in June 1994. This paper describes the system to be studied and the approach to be followed to complete the conceptual design by early 1997.
Both travelers were members of a nine-person US delegation that participated in an international workshop on accelerator-based 14 MeV neutron sources for fusion materials research hosted by the University of Tokyo. Presentations made at the workshop reviewed the technology developed by the FMIT Project, advances in accelerator technology, and proposed concepts for neutron sources. One traveler then participated in the initial meeting of the IEA Working Group on High Energy, High Flux Neutron Sources in which efforts were begun to evaluate and compare proposed neutron sources; the Fourth FFTF/MOTA Experimenters' Workshop which covered planning and coordination of the US-Japan collaboration using the FFTF reactor to irradiate fusion reactor materials; and held discussions with several JAERI personnel on the US-Japan collaboration on fusion reactor materials.
The construction and operation of an intense 14MeV neutron source is essential for the development and eventual qualification of structural materials for a fusion reactor demonstration plant (DEMO). Because of the time required for materials developed and the scale-up of materials to commercial production, a decision to build a neutron source should precede engineering design activities for a DEMO by at least 20 years. The characteristic features of 14MeV neutron damage are summarized including effects related to cascade structure, transmutation production, and dose rate. The importance of a 14MeV neutron source for addressing fundamental radiation damage issues, alloy development activities and the development of an engineering data bases is discussed. From these considerations the basic requirements and machine parameters are derived. 14 refs., 5 figs., 5 tabs.
This report describes a conceptual design of a high-fluence source of 14 MeV D-T neutrons for accelerated testing of materials. The design goal of 10 MW/m2 year corresponding to 100 displacements per atom per year is taken to be sufficient for end-of-life tests of candidate materials for a fusion reactor. Such a neutron source would meet a need in the program to develop commercial fusion power that is not yet addressed. In our evaluation, a fusion-based source is preferred for this application over non-fusion, accelerator-type sources such as FMIT because, first, a relevant 14 MeV D-T neutron spectrum is obtained. Second, a fusion source will better simulate the reactor environment where materials can be subjected to high thermal loads, energetic particle irradiation, high mechanical stresses, intense magnetic fields and high magnetic field gradients as well as a 14 MeV neutron flux of several MW/m2. Although the actual reactor environment can be realized only in a reactor, a fusion-based neutron source can give valuable design information of synergistic effects in this complex environment. The proposed small volume, high-fluence source would complement the capabilities of a facility such as ITER, which addresses toroidal fusion component development. For our source, the volume of reacting plasma and the fusion power have been minimized, while maintaining an intense neutron flux. As a consequence, tritium consumption is modest, and the amount of tritium required is readily available.