[en] Nuclear critical assembly (NCA) experiments simulating fuel rods and fuel storage racks under low moderator density conditions in the spent fuel pool (SFP) were conducted to obtain the criticality characteristic of the SFP during loss-of-coolant accidents. In these experiments, a 9 * 9 boiling water reactor (BWR) fuel assembly loaded in an aluminum, stainless steel, or borated stainless steel fuel storage rack was simulated and criticality experimental data such as critical water levels were obtained. It was realized that the aluminum storage rack cases had high reactivity against water densities in the test region due to neutron coupling effect. Then, the effective neutron multiplication factor k_eff values were calculated via the criticality safety assessment code MVP3.0 using libraries generated from JENDL-4.0 and ENDF/BVII.1. The discrepancies between the measure d and calculated k_eff values for all cases with various types of storage racks under various moderator densities were found to be within 250 pcm. In addition, there were some differences in k_eff between the two libraries possibly due to different ¹H in H₂O thermal scattering models: the k_eff values using ENDF/B-VII.1 showed positive biases of about 200 pcm in all test cases. (authors)