Developmeut of Subcriticality Monitor by Using Experimental

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A study on the development of a subcriticality monitor was performed by using the Kyoto University Critical Assembly (KUCA). Two experimental techniques of reactor kinetics, the coherence method between two neutron detectors and the Feynman-alpha method, were examined for the application to a subcriticality monitor.Through the present study, a subcriticality monitor was successfully established on the basis of the Feynmau-alpha method. On the other hand, it was found that some difficulties existed for the application of the coherence method ; for example, the efficiency of neutron detectors is not high enough.Combining a multi-channel scalar (MCS) unit with a personal computer, a new data bunching method was developed to shorten a processing time in the Feynman-alpha method. Using this method, a real-time measurement of subcriticality was demonstrated in experiments at the KUCA.Effects of the detector position and the dead time in measuring circuits were experimentaly examined to reduce the error in the subcriticality measurement. Finally, the subcriticality monitor based on the Feynman-alpha method was applied to subcriticality measurements of the poly-ethylene moderated and reflected cores constructed at the KUCA.Through a comparison of the measured results and the calculated ones by a multi-group Monte Carlo code KENO-IV,it was found that the subcriticality can be accurately measured down to around -5%DELTAk/k.