[en] It is important to accurately determine the degree of subcriticality in the system in which nuclear fuel units are dispersed so as to maintain subcritical condition. The degree of subcriticality is determined mostly by calculation. The experiment on criticality safety is frequently carried out on a critical system composed of plural subcritical units. In the Kyoto University critical assembly (KUCA), the measurement of the degree of subcriticality by pulsed neutron method has been carried out so far, but in fiscal year 1987, for the purpose of obtaining the experimental data at the time of criticality in a system composed of plural units, the experiment on a light water moderation, light water reflection core of division into two type was carried out at the C stand. This time, in the core of division into two type of C45 (5 rows) using a 4.54 mm pitch fuel frame, the change of criticality amount and neutron flux distribution were measured when the light water gap at the middle of the core was changed. The experiment and its results, the analysis using the SRAC system and the JACS code system and the results of calculation are reported. The research on the statical characteristics of the light water core of division into two type is expected to be carried out under other conditions. (Kako, I.)