Measurements and Analysis of Neutron Flux Distribution in UTR-KINKI

Abstract

The neutron flux distributions in UTR-KINKI are comprehensively analyzed in terms of the Au activation reaction rate and compared with those calculated by SRAC-CITATION and MCNP4C. The vertical distribution at the central stringer is found to be a cosine-like one with a smaller FWHM by about 15%, which is in good agreement with both simulation results within an RMS deviation of 2.4% and 2.1%, respectively. However, the CITATION fails to predict the horizontal distribution and humps in the vertical distribution in the fuel tank (FT) just outside the fuel meat due to low energy neutrons moderated in the H2O reflector region. It is suggested that the method of homogenization of the fuel assembly should be optimized to have satisfactory agreement with the measured distributions. On the contrary, the MCNP reproduces well the vertical distribution within the experimental uncertainty of ±3% in the FT and the horizontal distribution within the error of ±10%. From a little asymmetry of the distributions measured in the FT, it is implied that perturbation of the low energy neutron flux due to control rods or voids for them could be appreciable, and should be taken into account in the calculations in order to have even better agreement with the measured distributions.