Spent nuclear fuel chemical reprocessing plants process several 10(3) kg of spent nuclear fuel, especially Pu isotopes, which present significant potential for terrorism (Note: similar to 8 kg Pu constitutes a threat level quantity). This requires detecting actinides in transit, but also, to ensure they are not diverted. Present-day sensors disallow real-time monitoring leading to significantly non-optimal operations. The tensioned metastable fluid detector (TMFD) sensor technology has been developed by researchers at Purdue University in partnership with Texas A&M University, and various national laboratories (sponsored in part by several United States federal agencies and private enterprise). It is based on nano-to-macro scale interactions of radiation with molecules of fluids that are in a state of tensioned metastability. Developed are lab-scale prototypes for adapting to chemical reprocessing plants providing real-time directionality to within similar to 10 degrees-20, with similar to 90% efficiency to detect neutrons (from eV to MeV) and alpha emitting nuclides energies to within 1-5 key recoil resolution, and sensitivities to ultra-trace levels (e.g., to 10(-15) g/cc Pu). TMFD systems are robust, portable and offer 100x lower cost potential compared with present-day systems (e.g., NE-213 based neutron-gamma liquid scintillator based systems). A multiphysics design framework has been developed, and validated. This paper highlights state-of-art developments and adaptations of TMFDs for in situ, real-time monitoring of U, Pu, Am and Cm actinides from the sensitive (in the past virtually impossible to monitor) front-end wherein radioactively hot spent nuclear fuel is chopped and dissolved, to throughout the subsequent stages in a chemical nuclear fuel chemical process. (C) 2013 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.