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.
The coolant leakage by thermal striping phenomenon should be prevented at nuclear power plants and a lot of efforts are made to develop its evaluation methods. The frequency transfer function method can be used to obtain temperature and stress response to fluid temperature history using transfer function models; therefore it is considered as an excellent evaluation method. To measure temperature response of structures to fluid temperature variations and to confirm their frequency characteristics, transient temperature measurement tests were performed by JAEA. In the transient temperature measurement tests, three different frequencies of sinusoidal fluid temperature waves (0.05, 0.2, 0.5Hz) were controlled using frequency controlled thermal fatigue test equipment (SPECTRA) and temperature responses at inner and outer piping surfaces were measured along the test sections. Frequency effects on temperature attenuation during transfer process from fluid to structures were confirmed and the effective heat transfer function in frequency transfer function method was verified by transient temperature measurement test results.
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