Evaluation of -ray dose rates on the upper core structure of the experimental fast reactor Joyo

Ito, Chikara   ; Yamamoto, Takahiro; Maeda, Shigetaka   ; Ito, Hideaki; Sekine, Takashi 

In the experimental fast reactor Joyo, the upper core structure (UCS) was replaced. We have evaluated -ray dose rates on UCS in order to conduct radiation shielding design of the UCS cask and radiation exposure control in the UCS removal work. The -ray dose rates was calculated using the QAD-CGGP2R and corrected by the measured in-vessel axial distributions of -ray dose rate. In order to verify the -ray dose rate evaluation procedure, we measured spatial distribution of -ray on the surface of the cask, which contained UCS using plastic scintillating optical fiber (PSF) during the UCS removal work. The calculated PSF output values were approximately twice as large as measured through the UCS. Correcting the calculated -ray dose rates on the surface of the cask by results of the comparison has shown appropriate -ray dose rates distribution.