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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.
Successful development of fusion energy will require the design of high-performance structural materials that exhibit dimensional stability and good resistance to fusion neutron degradation of mechanical and physical properties. The high levels of gaseous (H, He) transmutation products associated with deuterium-tritium (D-T) fusion neutron transmutation reactions, along with displacement damage dose requirements up to 50-200 displacements per atom (dpa) for a fusion demonstration reactor (DEMO), pose an extraordinary challenge. The intense neutron source(s) is needed to address two complimentary missions: 1) Scientific investigations of radiation degradation phenomena and microstructural evolution under fusion-relevant irradiation conditions (to provide the foundation for designing improved radiation resistant materials), and 2) Engineering database development for design and licensing of next-step fusion energy machines such as a fusion DEMO. A wide variety of irradiation facilities have been proposed to investigate materials science phenomena and to test and qualify materials for a DEMO reactor. Currently available and proposed facilities include fission reactors (including isotopic and spectral tailoring techniques to modify the rate of H and He production per dpa), dual- and triple-ion accelerator irradiation facilities that enable greatly accelerated irradiation studies with fusion-relevant H and He production rates per dpa within microscopic volumes, D-Li stripping reaction and spallation neutron sources, and plasma-based sources. The advantages and limitations of the main proposed fusion materials irradiation facility options are reviewed. Evaluation parameters include irradiation volume, potential for performing accelerated irradiation studies, capital and operating costs, similarity of neutron irradiation spectrum to fusion reactor conditions, temperature and irradiation flux stability/control, ability to perform multiple-effect tests (e.g., irradiation in the presence of a flowing coolant, or in the presence of complex applied stress fields), and technical maturity/risk of the concept. Ultimately, it is anticipated that heavy utilization of ion beam and fission neutron irradiation facilities along with sophisticated materials models, in addition to a dedicated fusion-relevant neutron irradiation facility, will be necessary to provide a comprehensive and cost-effective understanding of anticipated materials evolution in a fusion DEMO and to therefore provide a timely and robust materials database.
The National Low-Temperature Neutron Irradiation Facility (NLTNIF), now constructed and currently being evaluated, will provide high radiation intensities and special environmental and testing conditions for qualified experiments at no cost to users. The NLTNIF will be of interest for both basic and applied research on fusion reactor materials. A general description and major specifications of the facility are presented along with recent results of the performance tests. In addition, a description is given of the procedure and experimental assemblies needed to perform experiments in the NLTNIF.
A fusion materials irradiation facility is required for the timely and cost-effective development of economical fusion power. Our conceptual machine provides sufficient neutron fluence for accelerated lifetime material tests in a time span of 1--2 y while producing less than 1 MW of fusion power. Neutral deuterium beams at 150 keV are injected into the center of a high-density warm tritium plasma housed in a 12-m-long cylindrical vessel. Superconducting magnets hold the plasma, which transfers the power to each end of the solenoid. The stainless steel end sections absorb the beam power and are externally cooled by high-pressure water to maintain the plasma-side wall temperature below 740 K.A service loop separates tritium from deuterium in the plasma effluent. Tritium is reinjected at each end. 9 refs., 2 figs., 2 tabs.

Fusion Policy

United States. Congress. House. Committee on Science, Space, and Technology. Subcommittee on Energy

Published: 1995

Total Pages: 536


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Any fusion reactor using tritium-deuterium fusion will be a prolific source of 14 MeV neutrons. In fact, 80% of the fusion energy will be carried away by these neutrons. Thus it is essential to calculate what will happen to them, so that such quantities as the tritium breeding ratio, the neutron wall loading, heat deposition, various kinds of material damage and biological dose rates can be determined. Monte Carlo programs, in particular the widely-used MCNP, are the preferred tools for this. The International Fusion Materials Irradiation Facility (IFMIF), intended to test materials in intense neutron fields with a spectrum similar to that prevailing in fusion reactors, also requires neutronics calculations, with similar methods. In some cases these calculations can be very difficult. In particular shielding calculations - such as those needed to determine the heating of the superconducting field coils of ITER or the dose rate, during operation or after shutdown, outside ITER or in the space above the test cell of IFMIF - are very challenging. The thick shielding reduces the neutron flux by many orders of magnitude, so that analog calculations are impracticable and heavy variance reduction is needed, mainly importances or weight windows. On the other hand, the shields contain penetrations through which neutrons may stream. If the importances are much higher or the weight windows much lower at the outer end of such a penetration than at the inner end, this may lead to an excessive proliferation of tracks, which may even make the calculation break down. This dissertation describes the author's work in fusion neutronics, with the main emphasis on attempts to develop improved methods of performing such calculations. Two main approaches are described: trying to determine nearoptimal importances or weight windows, and testing the "tally source" method suggested by John Hendricks as a way of biasing the neutron flux in angle.
The Rotating Target Neutron Source (RTNS-II) facility provides an intense source of 14-MeV neutrons for the fusion energy programs of Japan and the United States. Each of the two identical accelerator-based neutron sources is capable of providing source strengths in excess of 3 x 1013 n/s using deuteron beam currents up to 150 mA. The present status of the facility, as well as the various upgrade options, will be described in detail.