Critical Power Performance of the Tight-lattice Fuel Bundle

Currently, a reactor core for boiling water reactors (BWRs) which improves a conversion ratio to about 1 is being examined. Since the gap between fuel rods must be narrowed to about 1.3 mm, it is expected that the fuel cooling performance would deteriorate. However, there are few thermal-hydraulic measurement data for tight lattice rod bundle. Therefore, the thermal-hydraulic tests using the tight lattice bundle were carried out under the BWR operating condition. As a result, the boiling transition behavior was similar to the liquid film dryout, which is the boiling transition mechanism of the conventional BWR fuel bundle. Moreover, the tendency of thermal-hydraulic performance for the flow condition parameters was the same as for the conventional BWR. Next, the applicability of the correlation developed by Arai et al. was examined to evaluate the critical power. These test data could be predicted accurately by Arai's correlation. Arai's correlation is based on the measurement data obtained by LeTouneau et al. Thus, Arai's correlation is expected to have wide applicability for various tight lattice bundles.