Development of High Cycle Thermal Fatigue Evaluation Method Based on Time Interval of Peak-to-Peak of Fluid Temperature

2010 ◽  
Author(s):  
Nobuyuki Kimura ◽  
Jun Kobayashi ◽  
Hideki Kamide
Keyword(s):  
Thermal Stress ◽  
Thermal Fatigue ◽  
Temperature Fluctuation ◽  
Evaluation Method ◽  
Frequency Characteristics ◽  
Time Interval ◽  
Fluid Temperature ◽  
Cycle Number ◽  
The Core ◽  
High Cycle Thermal Fatigue

Hot and cold fluids are mixed at the core outlet of sodium cooled fast reactors. The temperature fluctuation causes high cycle thermal fatigue in structural components. The temperature fluctuation at the core outlet region does not have always a sinusoidal waveform but a sharp edged waveform. The temperature shows intermittent and sudden decrease and recovery like a spike form. It is necessary to take into account the spiky waveform of temperature fluctuation for the construction of an evaluation method of the high cycle thermal fatigue. The conventional method uses the amplitude and cycle number of waves without reference to the frequency of temperature fluctuation. In this study, the time interval of each wave based on the rainflow method was applied to consider frequency characteristics against the conversion from fluid temperature to thermal stress in structure. The thermal stress obtained from the new method was compared to the results of FEM analysis. It was found that the consideration of frequency characteristics of waves could evaluate the fatigue damage in structure. Furthermore, the frequency characteristics of waves in this method were expressed as the unified curve independent of the velocity. Hereby the new evaluation method could evaluate the thermal fatigue in the reactor.

Spectra Thermal Fatigue Tests Under Frequency Controlled Fluid Temperature Variation: Development of Test Equipment and Preliminary Tests

2004 ◽  
Author(s):  
Naoto Kasahara ◽  
Shinichi Hasebe ◽  
Sumio Kobaysashi ◽  
Masanori Ando ◽  
Nobuchika Kawasaki ◽  
...  
Keyword(s):  
Temperature Variation ◽  
Thermal Fatigue ◽  
Temperature Fluctuation ◽  
Evaluation Method ◽  
Mechanical Valve ◽  
Test Equipment ◽  
Frequency Effect ◽  
Measured Temperature ◽  
Fluid Temperature ◽  
Constant Flow Rate

High cycle thermal fatigue induced by fluid temperature fluctuation is one of the important issues in nuclear plants. JNC has proposed a fatigue evaluation method paying attention to temperature attenuation related with frequency of fluctuation. In order to clarify the frequency effect of fluid temperature fluctuation on the crack initiation and propagation, a sodium temperature controlled thermal fatigue test equipment (SPECTRA) was developed. This equipment is capable of preciously controlling sodium temperature variation under various frequencies with a constant flow rate. This performance was achieved by the control of electromagnetic pumps without mechanical valve operations. Specimens are long straight pipes where temperature fluctuation ranges gradually reduce from upstream to downstream. As preliminary tests, temperature measurement and fatigue experiments were conducted. Measured temperature was preciously controlled under various frequencies. Cracks were observed in upstream area of a specimen. From above results, capability of frequency controlled test by SPECTRA facility was confirmed.

Thermal Stress Response to Boundary Oscillation Between Hot and Cold Fluid Temperature

2014 ◽  
Author(s):  
Kohei Soda ◽  
Takato Mizutani ◽  
Naoto Kasahara
Keyword(s):  
Thermal Stress ◽  
Frequency Response ◽  
Response Function ◽  
Thermal Fatigue ◽  
Thermal Stratification ◽  
Frequency Response Function ◽  
Nuclear Power ◽  
Fluid Temperature ◽  
Thermal Striping ◽  
High Cycle Thermal Fatigue

In nuclear power plants, high cycle thermal fatigue induced by temperature fluctuation of the coolant is one of frequent failure modes. To ensure the safety of nuclear power plant systems, it is important to prevent thermal fatigue failure. Typical causes of high cycle thermal fatigue are thermal striping at Tee-junction and thermal stratification oscillation. In order to evaluate thermal stress caused by thermal striping, a frequency response function has been developed. This function was derived from a heat transfer and thermal elastic theories, and can adequately evaluate thermal stress induced by temperature gradient into wall-thickness direction. However, this theoretical method cannot adequately evaluate thermal stress by thermal stratification oscillation, because this phenomenon has the fluid temperature distribution gradient along axial direction. To investigate the mechanism of thermal stress generated by oscillation of thermal stratification, two types of models were studied. In the first type, fluid temperature oscillates with sinusoidal history at the same location, and in the second one, the boundary layer of hot and cold fluid temperature moves with sinusoidal velocity. Through clarification of the stress generation mechanism, the frequency response function was improved to evaluate stress by the thermal stratification oscillation. Applicability of this function was verified through agreement with finite element simulations.

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