Experimental fast reactor "JOYO" operational characteristics test report; Estimation of core characteristics by reactor noise analysis using in-core sensors installed in instrumented test assembly

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Instrumented test assembly (INTA) had been installed in experimental fast reactor JOYO from MK-Ii 8th duty cycle to the special testing cycle after 12th duty cycle. New information on core characteristics are obtained by noise analysis of various in-core sensors installed in INTA. (Flux monitor, thermocouples which measure fuel center and coolant temperature, et al.) They are not able to be obtained by conventional instrumentation. Main results are as follows. (1)Peak, existed in frequency band where space dependent characteristics is found, observed by ex-core flux monitor (about 410Hz) is induced by some phenomena outside fuel zone. (2)Transfer function between neutron flux and fuel center temperature successfully corresponds to analysis results which assumes time constant of fuel center temperature sensor is about 2 seconds. (3)Deterioration of fuel center temperature sensor can be detected or predicted by monitoring of its noise characteristics. (4)Time constant of thermal expansion of core support plate is estimated to be about 8 seconds.