Effective multiplication factor measurement by Feynman-$alpha method(4); Measurement of FBR type fuels

Mori, Tomoaki; Hazama, Taira 

The sub-criticality monitoring system has been developed for criticality safety management of nuclear fuel handling facilities. Low enriched MOX or uranium fuels have been used for sub-criticality measurements in the Deuterium Critical Assembly (DCA). This report describes the results of sub-criticality measurements for the core loaded with high enriched MOX fuels (JOYO MK-I fuels). The results of measurements showed that the prompt decay constant(), which was an index of the sub-criticality, was detected between Keff=0.64 and Keff=0.82 and the difference of about 0.08Keff could be detected. A simulation of sub-criticality measurements was performed with the Monte Calro code MCNP4A and the results were compared with measured values. The differences of values between calculations and measurements were less than 5%. It was confirmed that the sub-criticality measurements by Feynman- method could be simulated by MCNP4A code with enough accuracy. Feynman- method was applied to the DCA system as the neutron flux level was changed with time. It was confirmed that the common procedure of data processing had an enough ability to detect values for slow changes of neutron flux. On the other hand, the application of the differential filter was effective for fast changes of neutron flux.