An Integrated Approach to Precision Neutron Measurements in a Dynamic Environment

In a nuclear facility, precise neutron measurements may need to be taken for the purpose of quantifying the mass of safeguards-relevant nuclear material. However, this material is often located in an environment with substantial and fluctuating background noise due to other nuclear material located within the same process area. To control background, the nuclear material of interest is often transported from a working area to a dedicated shielded measurement area. This transportation of the safeguards-relevant nuclear material introduces new pathways for the material to be diverted by a would-be proliferator or stolen by a thief. Likewise, it increases the time required to take these critical measurements. This work aims to remove the transportation step from the process and enable the use of high precision non-destructive assay instruments in an environment with a dynamic background signal. A methodology is demonstrated which uses dispersed neutron detectors in a mock glovebox environment to quantify a dynamic background count rate and remove it from a high-level neutron coincidence counter measurement. This methodology builds upon previous efforts to develop an algorithm for localizing and quantifying sources within this mock glovebox environment by integrating said algorithm with a background change detection algorithm, a background signal inference algorithm, and a mass prediction algorithm to form a single methodology for making near real time nuclear material accountancy measurements. The effectiveness of this methodology is quantified experimentally by measuring the mass of a Cf-252 source in an environment where several other Cf-252 sources are moving throughout the room during the measurement. Over the course of a two-hour measurement, sources were moved within the gloveboxes to create ten distinct background configurations. Analysis of the resulting data yielded a 55.4% average error in the mass measurement when our methodology is not applied, and application of the methodology reduced the average error to -2.6%. This methodology serves as a proof of concept that precise non-destructive assay measurements can be taken inline at a nuclear process facility, thus reducing possible pathways for the diversion or theft of safeguardsrelevant nuclear material in addition to potentially enabling critical measurements to be taken more quickly.