Ryozo Yumoto, Hideyoshi Sasajima, Takashi Kajiyama, Akio Ohno, Iwao Kobayashi, Saburo Kikuchi, Kiyonobu Murakami, Takenori Suzaki, Harumichi Tsuruta, Shojiro Matsuura, and Masao Hashimoto
The disadvantage factor for thermal neutrons in light-water moderated PuO2-UO2 and UO2 square lattices were obtained from measurements of thermal neutron density distributions in a unit lattice cell, measured with Dy-Al wire detectors. The lattices consisted of 3.4w/o PuO2-UO2 and 2.6w/o UO2 fuel rods, and the water-to-fuel volume ratio within the unit cell was parametrically changed. The PuO2-UO2 and UO2 fuel rods were designed to realize equal fissile atomic number density. The disadvantage factors thus measured were 1.36±0.07, 1. 37±0.08, 1.40±0.06 and 1.38±0.06 in the PuO2-UO2 fuel lattices, and 1.30±0.06, 1.31±0.08, 1.30±0.08 and 1.33±0.06 in the UO2, for water-to-fuel volume ratios, of 1.76, 2.00, 2.38 and 2.95, respectively. This difference in disadvantage factor between PuO2-UO2 and UO2 fuel lattices corresponds to about 8%. Calculated results obtained by multigroup transport code LASER agreed well with the measured ones.