Development of analytical model for evaluating temperature fluctuation in coolant(XIII); Experimental investigations of stationary random temperature fluctuation characteristics in wall jet conditions

not registered; Otaka, Masahiko

Thermal striping phenomena characterized by stationary random tempeature fluctuations are observed in the region immediately above the core exit of liquid-metal-cooled fast breeder reactors (LMFBRs) due to the interactions of cold sodium flowing out of a control rod (C/R) assembly and hot sodium flowing out of adjacent fuel assemblies (F/As). Therefore the in-vessel components located in the core outlet region, such as upper core structure (UCS), flow guide tube, C/R upper guide tube, etc., must be protected against the stationary random thermal process which might induce high-cycle fatigue. In this study, frequency characteristics of stationary random temperature fluctuations were investigated by the use of the time-series data from a parallel wall jet experiment, TIFFSS-II.From the investigations, the following results have been obtained: [Time-Series Data Characteristics] (1)Larger temperature amplitudes were observed at more downstream distance thermocouples from the outlet plane of the jet nozzles. One of the main reasons for this behavior was considered to be that the thickness of laminar sub-layer was developed toward to downstream. [RMS value Characteristics of Temperature Fluctuations] (1)Lareger RMS values were calculated at more downstream distance thermocouples from the outlet plane of the jet nozzles. And the dependence on nozzle jet velocity was not clear. It was due to actualized buoyancy effects near the test piece wall. [Auto-Power Spectral Density Functions] (1)Higher frequency componets were increased drastically in sodium temperature fluctuations, due to the occurrence of the bursting behavior by existence of solid walls. [Coherence Functions] (1)Frequency bands having larger coherency values between temperature fluctuations were limited in a lower frequency components (<4.0 Hz) and a higher frequency components (>40.0 Hz). This frequency behavior characterizes fluid-structure thermal interaction phenomena in wall jet flows.