Subcriticality Monitoring with a Digital Reactivity Meter

Abstract

Feasibility of subcriticality monitoring with a digital reactivity meter was experimentally investigated using a sub-critical assembly. In the experiment, neutron detectors were placed in the reflector region where the neutron flux multiplied by the difference of the multiplication factor from unity is almost constant. The significant fluctuation of the neutron signal was filtered with a smoothing and a low-path filter of first order delay. In the subcritical system above with a constant neutron source, it was confirmed through the experiment that a digital reactivity meter with noise filtering module could give real time subcriticality when the detector was placed at appropriate positions. Based on the experiment, we have proved that the reactivity meter can be used for monitoring the subcriticality on a real time basis.