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

Abstract

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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Notes on contributors

M. A. Abdou

Mohamed A. Abdou is a professor in the Department of Mechanical, Aerospace, and Nuclear Engineering at the University of California, Los Angeles (UCLA) and also is the director of fusion technology at UCLA. His research interests include neutronics, thermomechanics, fusion technology, and reactor design and analysis. He served as the U.S. leader of the Japan Atomic Energy Research Institute (JAERI)/U.S. Department of Energy (U.S. DOE) collaboration on fusion blanket neutronics.

H. Maekawa

Hiroshi Maekawa (BE, 1965; MS, 1967; and Dr. Eng., 1970, nuclear engineering, Tokyo Institute of Technology, Japan) is the deputy director of the Department of Reactor Engineering and the head of the Intense Neutron Source Laboratory at JAERI. He has worked on fusion neutronics for more than 20 years, and he planned and constructed the Fusion Neutronics Source (FNS) facility. He served as the Japanese leader of the JAERI/U.S. DOE collaboration on fusion blanket neutronics. His recent research has focused on International Fusion Materials Irradiation Facility conceptual design activities.

Y. Oyama

Yukio Oyama (BS, physics, 1975, MS, nuclear physics, 1977; and Dr. Eng., 1989, Osaka University, Japan) is a principal scientist at JAERI. He has worked in the area of fusion neutronics experiments since 1978. He is currently involved in intense and high-energy neutron source projects.

M. Youssef

Mahmoud Z. Youssef (PhD, nuclear engineering, University of Wisconsin, 1980) is a senior research engineer in the Department of Mechanical, Aerospace, and Nuclear Engineering at UCLA. He participated in several conceptual magnetic fusion energy and inertial fusion energy reactor design studies with emphasis on nuclear analysis and blanket/shield design. His research interests are in the areas of blanket/shield design optimization, nuclear data, sensitivity/uncertainty studies, neutronics methods and code development, tritium fuel cycle, radioactivity and safety aspects of fusion, integral experiments, neutronics testing, and research and development for fusion reactors, particularly the International Thermonuclear Experimental Reactor (ITER).

Y. Ikeda

Yujiro Ikeda (PhD, nuclear engineering, Nagoya University, Japan, 1981) is head of the Fusion Neutronics Laboratory in the Department of Reactor Engineering at JAERI. He has worked in the areas of fusion neutronics experiments, induced radioactivity experiment and analysis, direct nuclear heating measurements, activation cross-section measurements, and fusion dosimetry.

A. Kumar

Anil Kumar (PhD, University of Bombay, India, 1981) is senior development engineer at UCLA. His current research interests include fusion reactor nucleonics experiments and analysis, technique development for nuclear heating, decay heat measurements, biological dose, fusion diagnostics, safety factor methodology for fusion reactor design parameters, low-activation materials, inertial confinement fusion, and sequential reactions. He has conducted experiments at leading facilities such as the FNS facility in Japan, the Tokamak Fusion Test Reactor (TFTR) at Princeton University, and LOTUS in Switzerland.

C. Konno

Chikara Konno (MS, physics, Kyoto University, Japan, 1985) is a research scientist in the Department of Reactor Engineering at JAERI. He has worked in the areas of fusion neutronics experiments, cross-section measurements, and neutron spectrum measurements using a proton-recoil counter.

F. Maekawa

Fujio Maekawa (MS, nuclear engineering, Osaka University, Japan, 1990) is a research scientist at JAERI. He has been engaged in integral experiments for fusion neutronics and studied the behavior of neutron, photon, and electron transport in media. His current interests are in the measurements of tritium and decay heat of irradiated materials.

K. Kosako

Kazuaki Kosako (BE, atomic engineering, Tokai University, Japan, 1984) has worked at Sumitomo Atomic Energy Industries since 1994. He worked in the Department of Reactor Engineering at JAERI from 1984 to 1992 where he was involved mainly in fusion neutronics. He is currently interested in the area of radiation damage of materials.

T. Nakamura

Tomoo Nakamura (BS, physics, Kyoto University, Japan, 1957) is currently director of the Public Acceptance Database Center, Research Organization for Information Science and Technology. His research background includes experimental reactor physics on fast breeder reactors and nuclear technology on fusion reactor blankets. He served as the former Japanese leader of the JAERI/U.S. DOE collaboration on fusion blanket neutronics.

E. Bennett

Edgar F. Bennett (PhD, University of New Hampshire, 1957) is a physicist at Argonne National Laboratory. He has been a section head of experimental reactor physics since 1970. He is best known as the inventor of a widely used in-core proton-recoil spectrometer– a technique that he has been continually updating. He has also made contributions to the field of reactivity measurement by reactor noise techniques, in particular, by providing a common theoretical basis and introducing a new type of variance experiment.