Simultaneous measurements of neutronic noise with fluctuation of inlet coolant temperature and vibration of a control rod at KUR

Experiments on reactor noise were conducted at KUR. Depending on the operating condition of the reactor, the cause of the noise are classified into the following four types. (1) Zero-power noise source due to the branching process of fission neutrons and/or due to random bombardment of neutrons to the detector ----- under natural circulation of coolant and at essentially zero-power level. (2) Coolant temperature fluctuation due to natural convection ----- under natural circulation and at relatively high power level. (3) Flow induced vibration of shim control rods ----- under forced circulation of coolant and at low power level. (4) Fluctuation of inlet coolant temperature ----- under forced circulation and near the maximum power level. Vibration of a spare shim control rod and fluctuation of inlet coolant temperature were measured simultaneously with the neutronic noise. Then the noise sources of the type (3) and (4) were verified. The vibration of a control rod has a broad spectrum in low frequency region besides the large peak at 14 Hz. The fluctuation of inlet coolant temperature is nonwhite noise and consists of large low frequency component. The theoretically predicted sink structures in the neutronic PSD (power spectral density) relating to the transit time of inlet coolant temperature fluctuation through the core were not observed in the experimental results. (auth.)