JAPAN ATOMIC-ENERGY RESEARCH-INSTITUTE UNITED-STATES INTEGRAL NEUTRONICS EXPERIMENTS AND ANALYSES FOR TRITIUM BREEDING, NUCLEAR HEATING, AND INDUCED RADIOACTIVITY

A large number of integral experiments for fusion blanket neutronics w ere performed using deuterium-tritium (D-T) neutrons at the Fusion Neu tronics Source facility as part of a 10-yr collaborative program betwe en the Japan Atomic Energy Research Institute and the United States. A series of experiments was conducted using blanket assemblies that con tained Li2O, beryllium, steel, and water-coolant channels with a point neutron source in a closed geometry that simulated well the neutron s pectra in fusion systems. Another series of experiments was conducted using a novel approach in which the point source simulated a pseudo-li ne source inside a movable annular blanket test assembly, thus providi ng 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 m easurement techniques were developed for tritium production, induced r adioactivity, and nuclear heating. Transport calculations were perform ed using three-dimensional Monte Carlo and two-dimensional discrete or dinates codes and the latest nuclear data libraries in Japan and the U nited 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 sh ould use a safety factor > 1.1 to 1.2, depending on the calculation me thod. Such a safety factor may not be affordable with most candidate b lanket designs. Therefore, demonstration of tritium self-sufficiency i s recommended as a high priority for testing in near-term fusion facil ities such as the International Thermonuclear Experimental Reactor (IT ER). The radioactivity measurements were performed for > 20 materials with the focus on gamma emitters with half-lives < 5 yr. 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 case s exceeding 5 and others falling below 0.1. Most discrepancies were at tributed directly to deficiencies in the activation libraries, particu larly errors in cross sections for certain reactions, A microcalorimet ric technique was vastly improved, and it allowed measurements of the total nuclear heating with a temperature rise as low as 1 mu K/s. The C/E ratio for nuclear heating deviated from 1 by as much as 70% for so me materials but by only a few percent for others.