Development of analytical model for evaluating temperature fluctuation in coolant (XII); Investigation of stationary random temperature fluctuation characteristics in frequency domain

PNC TN9410 98-013, 48 Pages, 1998/03

PNC-TN9410-98-013.pdf:1.51MB

Thermal striping phenomena characterized by stationary random temperature fluctuation 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 parallel impinging jet experiments, TIFFSS-I. From the investigations, the following results have been obtained; [Auto-Power Spectral Density Functions] (1)Higher frequency componets were decreased drastically with the close to the test piece surface, due to the presence of filtering effect by the laminar sub-layer and heat tansfer to the surface from coolant. (2)Dependence to the nozzle velocities was observed at the outside and inside positions of the laminar sub-layer region. It was due to the increasing of turbulent intensities with increase of the nozzle velocities. [Coherence Functions] (1)Coherency between outer temperatures of the laminar sub-layer was very small. 0ne of the main reasons is that the outer temperatures of the laminar sub-1ayer were dominated by the stationary random phenomena of turbulence flows. (2)It was confirmed that the coherency between immediate positions of different thermocouples had relatively higher values. [Transfer Functions] (1)The dominant frequency band of the gain was about 3 - 10 Hz for the transfer functions of the outer position to the inner position of the laminar sub-layer, and of the inner position of the laminar sub-layer to the test piece surface. (2)There wasno dependence of ...

Study on in-service calibration method for electromagnetic flowmeter

Endo, Akira

PNC TN941 85-97, 221 Pages, 1985/07

PNC-TN941-85-97.pdf:5.54MB

In liquid metal cooled fast breeder reactors (LMFBRs), electro-magnetic flowmeters (EMFs) have been extensively used, because they have satisfactory properties as the instrumentation sensor including the radiation-resistance and it is easy to assure tightness of the coolant boundary. In consideration of impotance of the flowrate measurement and the EMFs degradiation, it is necessary to calibrate them at appropriate time intervals as well as other instruments. However it is difficult to remove the EMF from the cooling system and the calibration by real flow in a test loop is almost impossible, because the pipe of the EMF makes up the coolant boundary. Therefore, it has been desired to develop a simple and accurate calibration method without removing the EMF from the system. The possibility to make use of the correlation method, which is simple and able to be applied in service condition, was suggested. In the method, the transit time of the fluid is obtained from the correlation between the output voltage flucluations observed by two pairs of electrodes attached to the pipe along the fluid flow direction, and then the flow rate can be calculated. However, the correlation method has not been applied practically to EMF calibration, because there are problems that the flow rate measured by correlation method inclines to larger side than true one and shows too large scattering. In this thesis, first the process in which the turbulent behavior of the flowing fluid is transformed into the voltage fluctuation is considered and it is shown that the transit velocity of the fluctuation obtained by the correlation method is affected by the flow velocity near the center of the pipe rather than cross-sectional mean flow velocity. That is, since the output voltage of EMF is expressed by an integral of the flow velocity multiplied by a weighting function depending on the location over the whole cross-section of the pipe, the transit velocity of the voltage ...