When an assembly in a core is partially blocked, the temperature in the upper plenum fluctuates at an early stage. Therefore, the temperature fluctuation in the upper plenum can provide the information about a local blockage of an assembly. For developing the detection algorithm for the partial blockage, we analyzed the temperature fluctuation in the upper plenum due to the partial blockage in an assembly. The LES turbulence model in the CFX code was used for analyzing the temperature fluctuation in the upper plenum because the LES is suitable for analyzing the time dependent turbulence variables. After analyzing the temperature fluctuations in the upper plenum, we established basic design requirements for the flow blockage detection system through a FFT analysis and some statistical analysis. We concluded that response time of a measuring device was less than 13 m s and that it should cover a high temperature range of 1000 K. In addition, the resolution of the thermocouple was less than 2 K and its location should be within 25 cm from the exit of each assembly. (c) 2005 Elsevier Ltd. All rights reserved.
