Experiment planning of subcritical reactivity measurements using high order statistics of neutron counting

The reactivity measurement of subcritical fissile arrangements (subcriticality) is a featured subject among those in reactor physics, because it is necessary to handle, process, and transport fissile material from nuclear installations safely. None of the many available experimental methods of subcriticality measurements used nowadays allows its direct determination; however, the third order correlation of neutron counting allows subcriticality estimation from a fissile material without any previous knowledge of its kinetic parameters or any pulsed neutron source. Despite of its intrinsic advantages, high order statistics requires a careful planning and an optimized procedure because this type of experiment demands a long acquisition time when compared to the usual methods. It is estimated that such procedure could ask for acquisition times a few orders of magnitude longer than those required by the usual methods of subcriticality estimation (for similar uncertainties). The main experimental results of this work, undertaken in the IPEN/MB-01 facility (a zero power reactor), which agreed with the simulated results obtained by dedicated Monte Carlo codes, were: the long time for data acquisition to obtain an useful result (hundreds hours of acquisition time), and the higher efficiency of using saturation time channels different from those which were used by others researches.