Reactor Pulse Tracking using Micro-Pocket Fission Detectors in Research Reactors

A series of experiments are reported which serve as milestones in the development of the MPFD technology. Each test involved reactor pulsing, a controlled power excursion that results from rapid removal of control rods. During a reactor pulse, the power level increases by several orders of magnitude in a fraction of a second resulting from prompt-critical neutron generation in the core. Preliminary reactor pulse testing was conducted at the Kansas State University TRIGA Mk. II nuclear reactor (KSU). The MPFD was used to track reactor pulses of $2.77 and $2.50 worth of reactivity insertion with measured Full Widths at Half Maximum (FWHM) of 13.2 and 16.1 ms compared to theoretical FWHM of 12.2 and 14.4 ms using the Fuchs-Nordheim Model. At the University of Wisconsin Madison Nuclear Reactor (UWNR), a set of 7 detectors, each with 4 independent chambers was deployed as part of the NEUP-NEAMS collaboration between UWNR and KSU. Nine of the time-synchronized chambers were able to track six reactor pulses to provide a spatial map of neutron flux. Finally, a two-chamber MPFD was deployed inside the Idaho National Laboratory Transient Reactor Test Facility (TREAT) reactor core and successfully monitored the power excursion of a 15 GW reactor pulse with an estimated neutron flux of ~10¹⁸ n/cm2/s. These preliminary tests highlight the multi-faceted capability of the MPFD as an instrument in different research and power reactors.