[en] To begin the removal of fuel debris at Fukushima Dai-ichi Nuclear Power Station, the consequences of possible criticality accidents must be evaluated in advance. Predictions of the region-dependent number of fissions can be especially important. Such evaluations are necessary for dose evaluations for workers, machines and the public. In this work, instead of traditional point kinetic analysis, space-dependent kinetic analysis was performed using the MIK code, which is a unique method based on Monte Carlo neutron transport calculations. The target of analysis was a simple spherical fuel system where fissile regions are coupled weakly in terms of neutronics. Specifically, we sought to reveal the relationship between the water level surrounding the fuel debris and the region-dependent number of fissions during criticality accidents, as it is thought that the water level surrounding the fuel may influence both the reactivity and the weakly coupling between fissile regions and have an impact on the region-dependent number of fissions. Through the observation of C_ij function, which is a key parameter for space-dependent kinetic analysis using the MIK code, the characteristics of weakly coupled systems are revealed. In addition, the relationship between the water level and the region-dependent number of fissions at supercritical condition is evaluated and discussed. (authors)