[en] Power distributions of mixed-oxide (PuO₂-UO₂) fuel rods in light-water lattices were measured using a light-water critical assembly to study reactor physical characteristics in the plutonium utilization to light-water reactor. The power distributions were measured about the test fuel rods; five kinds of PuO₂-UO₂ fuel rods and six kinds of UO₂ fuel rods changing PuO₂ and ²³⁵U enrichments respectively. In the PuO₂-UO₂ and UO₂ lattices, horizontal power distributions were measured by gamma scanning technique changing width of gap water and arrays of the test fuel rods parametrically. The effects of the parameters to the power distributions were obtained and the local power peaking factors of a BWR type fuel assembly were also measured for several test fuel rod arrays. Although it has been considered that the island loading pattern PuO₂-UO₂ fuel rods are loaded in the internal region of a fuel assembly and UO₂ rods surrounding those, is more effective to guarantee reactivity worth of control rods, the above results show that the inverse loading pattern PuO₂-UO₂ fuel rods are in the peripheral region, is more easy to attain power. (author)