Patent ID: 8842797

Claim:
Gamma scanning apparatus comprising: a gamma-ray detector; a collimator that limits a measuring range in a fuel assembly and limits entry of gamma rays from the fuel assembly into the gamma-ray detector; an absorber that controls intensity of the gamma rays entering the gamma-ray detector; a shield that shields the gamma-ray detector; a housing that contains the gamma-ray detector, the collimator, the absorber, and the shield; moving and fixing means that moves the housing to a definite position and fixing the housing thereto; rotating and moving means that moves the fuel assembly vertically in addition to rotating the assembly; a gamma-ray counting circuit that measures an output of the gamma-ray detector; and data collecting/analyzing and controlling apparatus that analyzes data output from the gamma-ray counting circuit, in association with data relating to the rotation and movement of the fuel assembly by the rotating and moving means; wherein: the rotating and moving means, after fixing the vertical position of the fuel assembly with that of the housing, rotates the fuel assembly through 360 degrees with its height kept constant, at a fixed or variable angular velocity; during the 360-degree rotation of the fuel assembly, the gamma-ray counting circuit measures either a time average of any count values which the gamma-ray detector has detected during the rotation of the fuel assembly (i.e., an average counting rate), or an integral value of any counts detected within a fixed time by the detector; and the data collecting/analyzing and controlling apparatus analyzes the data output from the gamma-ray counting circuit, in association with the data relating to the rotation and movement of the fuel assembly by the rotating and moving means, and thus derives a burn-up distribution and power distribution of the fuel assembly.