Study on pressure drop of tight lattice rod bundle

There is a possibility of the fuel assembly design with tightened fuel rod pitch for higher conversion ratio for Boiling Water Reactor (BWR). Pressure drop is one of the design key parameters to evaluate the possibility of BWR core with higher conversion ratio. The pressure drop test for tight lattice rod bundle under steady conditions has been done under BWR fluid conditions. It is found that the developed prediction method has the reasonable performance for lower mass flux region and it is necessary to improve the predicted accuracy for high mass flux. (J.P.N.)