[en] In order to predict the critical power of a BWR rod bundle by calculation, we have developed a fuel rod spacer effect model for quantitative estimation of the spacer effect on film flow on a fuel rod surface. Unknown parameters introduced in the spacer effect model are determined, based on critical power test data conducted at the Toshiba 4 x 4 bundle test loop. In this parameter estimation procedure, a boiling transition (BT) rod position effect is included, using critical power test data in which BT is expected to occur at different rod positions. The spacer model developed in the present program has been implemented in the film flow model subchannel analysis code CRIP version 2, and the calculated critical power is compared with the 4 x 4 bundle test data. The results of measurement and analysis show good agreement. (author)