"JOYO" Start-up test report; Reactor noise analysis

Sanda, Toshio*; not registered; not registered; not registered; not registered; Muramatsu, Toshiharu; Sekiguchi, Yoshiyuki*

As part of dynamics tests in the experimental fast breeder reactor "JOYO", reactor noise tests were carried out. At some power levels, up to 50MW, fluctuations of the flux, the outlet, temperatures of fuel assemblies and temperatures of primary and secoudary main cooling loops were measured. The power spectral density, correlation function, transfer function and coherence function of these signals were obtained and reactor characteristics were analyzed. The major results are as follows. (1)It was confirmed that no unstable phenomenon exists in JOYO. (2)At low frequency region, fluctuations of these signals are larger and give better correlations. At this region, the primary contributors to fluctuations of the flux and the reactor outlet temperature were investigated. (3)In power spectral density of the flux, the noticeable peaks exist at about 1.8Hz and 0.025Hz. The former peak is due to control rod vibration effect and the latter peak has reactor power dependency and the neutron detector position dependency. (4)By the correlation functions of the secondary cooling loop temperatures, coolant transport delay times were obtained, which showed good agreement with the times calculated by flow velocity and the pipe length.