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Japan Atomic Energy Research Institute/United States Integral Neutronics Experiments and Analyses for Tritium Breeding, Nuclear Heating, and Induced Radioactivity

M. A. Abdou, H. Maekawa, Y. Oyama, M. Youssef, Y. Ikeda, A. Kumar, C. Konno, F. Maekawa, K. Kosako, T. Nakamura, E. Bennett

Fusion Science and Technology / Volume 28 / Number 1 / Pages 5-38

August 1995

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A large number of integral experiments for fusion blanket neutronics were performed using deuterium-tritium (D-T) neutrons at the Fusion Neutronics Source facility as part of a 10-yr collaborative program between the Japan Atomic Energy Research Institute and the United States. A series of experiments was conducted using blanket assemblies that contained Li2O, beryllium, steel, and water-coolant channels with a point neutron source in a closed geometry that simulated well the neutron spectra in fusion systems. Another series of experiments was conducted using a novel approach in which the point source simulated a pseudo-line source inside a movable annular blanket test assembly, thus providing a better simulation of the angular flux distribution of the 14-MeV neutrons incident on the first wall of a tokamak system. A number of measurement techniques were developed for tritium production, induced radioactivity, and nuclear heating. Transport calculations were performed using three-dimensional Monte Carlo and two-dimensional discrete ordinates codes and the latest nuclear data libraries in Japan and the United States. Significant differences among measurement techniques and calculation methods were found. To assure a 90% confidence level for tritium breeding calculations not to exceed measurements, designers should use a safety factor >1.1 to 1.2, depending on the calculation method. Such a safety factor may not be affordable with most candidate blanket designs. Therefore, demonstration of tritium self-sufficiency is recommended as a high priority for testing in near-term fusion facilities such as the International Thermonuclear Experimental Reactor (ITER). The radioactivity measurements were performed for >20 materials with the focus on gamma emitters with half-lives <5yr. The ratio of the calculated-to-experimental (C/E) values ranged between 0.5 and 1.5, but it deviated greatly from unity for some materials with some cases exceeding 5 and others falling below 0.1. Most discrepancies were attributed directly to deficiencies in the activation libraries, particularly errors in cross sections for certain reactions. A microcalorimetric technique was vastly improved, and it allowed measurements of the total nuclear heating with a temperature rise as low as 1 µK/s. The C/E ratio for nuclear heating deviated from 1 by as much as 70% for some materials but by only a few percent for others.

 
 
 
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