Rod displacement effect on thermal-hydraulic behaviour in tight-lattice bundle based on X-ray CT measurement

Mitsutake, Toru*; Akimoto, Hajime; Misawa, Takeharu; Kureta, Masatoshi*; Katsuyama, Kozo* ; Nagamine, Tsuyoshi*; Matsumoto, Shinichiro*

An inside-structure observation of a tight-lattice 7-rod bundle was made, using the high-energy X-ray computer tomography(CT) apparatus. The two-dimensional configurations of all rods were obtained at seventy-six axial height positions over the whole length of the bundle. The measured results of the rod positions showed small rod position displacements, about 0.5 millimeters at maximum, from the lattice positions. Based on these measured rod position displacement results, the flow area, equivalent hydraulic diameter, rod-rod clearance, and rod-shroud clearance were calculated. The effect of rod position displacement on critical power was estimated by a sub-channel analysis. The result showed that the rod position displacement effect has only a small effect on critical power calculations. The calculated critical power still overestimated the measured value.