EVALUATION OF LOCAL-POWER DISTRIBUTION WITH FINE-MESH CORE MODEL FOR HIGH-TEMPERATURE ENGINEERING TEST REACTOR (HTTR)

In the high temperature gas-cooled reactors (HTGRs). the radial and ax ial heterogeneity resulted from a combination of fuel rods, burnable p oison rods, block end graphite and so on causes local power peakings w hich increase the fuel temperature locally. An method was developed fo r calculating the local power and the fuel temperature distributions. This method deals with all heterogeneity effects of a whole core in th e radial and axial directions with a design code system including a ve ctorized 3-dimensional diffusion code. The uncertainty of the method h ad been evaluated through the analyses of the power distribution obtai ned by critical experiments with the Very High Temperature Reactor Cri tical Assembly (VHTRC). The difference was less than 3% between the ca lculated and measured power distributions. From the results, it was co nfirmed that this method could predict the local power distribution of the HTGR with high accuracy. This method was applied to the evaluatio n of the fuel temperature of the HTTR. It was shown that the maximum f uel temperature would be lower than the design limit of 1,495-degrees- C for the normal operation and that of 1.600-degrees-C for the anticip ated operational transients.