Recent Research Activities on CANDLE Burnup

Abstract RECENT RESEARCH ACTIVITIES ON CANDLE BURNUP. A new reactor burnup strategy CANDLE (Constant Axial shape of Neutron flux, nuclide densities and power shape During Life of Energy producing reactor) was proposed in 2000, where shapes of neutron flux, nuclide densities and power density distributions remain constant but move upward (or downward) along its core axis. Since then many research activities have been performed in Tokyo Tech. In this paper these activities are summarized, and some other important activities relating CANDLE burnup performed in the other institutes in the world are also introduced. Keywords : CANDLE, burnup, fast reactor, long-life reactor, safe, proliferation resistant 1. Introduction: Concept CANDLE stands for Constant Axial Shape of Neutron Flux, Nuclide Densities and Power Shape During Life of Energy Production [1, 2]. The abbreviation also represents the candle-like burnup. burning Figure 1 . CANDLE burnup strategy. (Note that the moving direction can be the opposite of that illustrated. The core height is illustrated here to be extremely long to make the explanation easy.) As shown in Figure1, when this burnup strategy is used, the burning region moves at a speed proportionate to the power output along the direction of the core axis without changing the spatial distributions of the nuclide densities, neutron flux, or power density. What is significant is that even though the fuel is fixed in the core, it is not necessary to use movable devices to control the burnup, such as control rods and reflector control, as is the case in conventional reactor design. Note that the core height has been illustrated as being extremely long to make it easy to show the characteristics of the burnup strategy. In a normal core however, the combined length of the spent fuel and fresh fuel regions is much shorter than that of the burning region. Figure4, presented later, better illustrates an actual reactor; though even in Figure4, the moving distance is shown as being long. Note also that although in Figure1 the burning region is shown as moving from the top to the bottom, it is possible to have the region