Fast Neutron Collar (FNCL) Instrument Advancements

A multi-disciplinary research team at Lawrence Livermore National Laboratory (LLNL) is investigating advanced hardware components, signal processing and analysis methodologies that could substantially improve operational capabilities of the CAEN SyS VeryFuel Fast Neutron Collar (FNCL) instrument for safeguards applications. This effort is addressing the following two components of the baseline FNCL instrument: • Hardware advancement focused on fast neutron detector array assemblies, spanning a range of design options, including the choice of scintillation material, individual cell size, light readout, shielding, and moderation for improved neutron and gamma-ray efficiency, pulseshape discrimination, pile-up rejection, and cross-talk reduction capabilities. • Signal processing and data analysis tools for waveform characterization and neutron correlation evaluations, that could provide a self-contained estimate of the fissile material loading without relying on calibration curves and potentially eliminating an active interrogation source. The objective for developing hardware and software alternatives is to further extend FNCL instrument capabilities and implement a robust combination of effective detection and pulse processing techniques with analysis methodology that will not require a priori empirical calibrations for a specific type of unirradiated fuel assemblies. All hardware and software modifications have been evaluated as add-ons to the baseline FNCL unit currently available at LLNL. The newly designed detector array panels will operate with the existing data acquisition hardware. The data acquisition and analysis scripts will be executed on the FNCL control computer in parallel to the current manufacturer-supplied software. The hardware and analysis approaches developed in this effort are evaluated in comparison with the performance of the baseline FNCL instrument in laboratory experiments in a passive regime and with a range of neutron interrogation sources, using test objects with a varying amount of uranium. Critical performance parameters were determined to quantitatively characterize improvements in the FNCL operational capabilities for each new hardware solution and components of the analysis workflow.