Analysis Of In-line Plutonium Mass Measurements, In A Dynamic Background Environment, For Nuclear Material Control And Accounting In Nuclear Fuel Cycle Facilities

In nuclear material production environments Non-Destructive Assay (NDA) is an important part of Nuclear Material Control and Accounting (NMC&A), and these NDA measurements can take place in a direct radiative environment with dynamic background. Dynamic background is due to the continuous movement of nuclear material among glove boxes and within them. In-line or at-line measurements have the benefit of requiring less material moves and can offer quicker measurement results than moving nuclear material to designated NDA laboratories. To perform agile in-line measurements, one must characterize changing background. To this aim, we built our own test bed consisting of a set of the glove boxes, a moving trolley rail, and an array of 3He neutron detectors. In this research we characterize the dynamic background using an array of 3He neutron detectors mounted on gloveboxes and evaluate the performance of the in-line NDA instrument with a High-Level Neutron Coincidence Counter (HLNCC) placed under a glovebox. Plutonium oxide items were placed in the HLNCC to measure plutonium mass and subsequent uncertainty while different configurations of 252Cf neutron sources inside the gloveboxes, and on the rail, created the background signal, while at the same time, the measurements of Plutonium are performed using the HLNCC. Real time measurements from the 3He detector array are used to track and characterize the dynamic background in real time, and its effect on Pu mass assay uncertainty is evaluated. Within this paper, we will discuss the results of these measurements and we will drive conclusions towards theapplicability of international and domestic safeguards for reliable and verifiable NMC&A in complex large-mass, many item mass-accounting processing facilities.