Evaluation of Local Power Distribution with Fine-mesh Core Model for High Temperature Engineering Test Reactor (HTTR)

Abstract

In the high temperature gas-cooled reactors (HTGRs), the radial and axial heterogeneity resulted from a combination of fuel rods, burnable poison rods, block end graphite and so on causes local power peakings which increase the fuel temperature locally. An method was developed for calculating the local power and the fuel temperature distributions. This method deals with all heterogeneity effects of a whole core in the radial and axial directions with a design code system including a vectorized 3-dimensional diffusion code. The uncertainty of the method had been evaluated through the analyses of the power distribution obtained by critical experiments with the Very High Temperature Reactor Critical Assembly (VHTRC). The difference was less than between the calculated and measured power distributions. From the results, it was confirmed that this method could predict the local power distribution of the HTGR with high accuracy. This method was applied to the evaluation of the fuel temperature of the HTTR. It was shown that the maximum fuel temperature would be lower than the design limit of 1,495°C for the normal operation and that of 1,600°C for the anticipated operational transients.