Monitoring of Nuclear Material Movements at a Reprocessing Plant G. Janssens-Maenhout 1 , L. Dechamp, Z. Dzbikowicz Institute for the Protection and Security of the Citizen Joint Research Centre, European Commission Via Fermi, Ispra 21020 (VA) Italy E-mail: greet.maenhout@jrc.it, luc.dechamp@jrc.it, zdzislaw.dzbikowicz@jrc.it Abstract: A process monitoring software tool has been developed, which allows inspectors a remote verification of nuclear material movements based on the interpretation of neutron and gamma signals, which are measured during the trajectory and online analysed. Neither supervision nor control is intended with the software but a checking of the required coherency and conformity with safeguards purposes. The data analysis and interpretation kernel supports the inspector in the back-end of the nuclear fuel cycle and allows in particular near real time accountancy in a reprocessing plant. To monitor the nuclear material flow for near real time accountancy purposes a diagnostic aid for the inspectorate was conceived, which interprets data from solution and powder measurements of different kind and at different steps in the process. In a first step tank transfers have been analysed by syntactic pattern recognition and introduction of functional blocks. A predefined sequence of functional blocks yields a tank signature and characterises unambiguously the filling rates, normal operation tank levels, levels for stirring and skimming, and the emptying rates. In a second step the same approach has been applied to the cyclic behaviour of a weighing scale. The weighing procedure with first scale-recalibration check, with the filling of Pu powder cans and with the final inventory weight determination could be verified remotely. Finally this syntactic pattern recognition approach has been applied to follow the movement of nuclear material by treating the neutron and gamma signals. This paper reports on the analysis of the neutron and gamma signals for the remote follow-up of the spent fuel assemblies on their way to and from the measurement pit. A real-time analysis of the signal from the neutron counter simultaneously to the signal of the gamma counter positioned under a fixed geometry allows an identification of a movement signature. The functional blocks describing the movement signature consist of peaks and plateau's. The auto-correlation of a predefined sequence with the real sequence based on the measured neutron and gamma counts allows to characterise the nuclear material moved in the channel towards and from the measurement pit. With the appropriate parameters such as peak height and plateau length the software monitors if the material movement procedure is followed conform to the safeguards purposes. Keywords: process monitoring; neutron/gamma signal interpretation. 1 The author is part-time professor at the University of Ghent, Faculty of Engineering, Department Electrical Energy, Systems and Automation. 1. Introduction Process monitoring is an excellent tool to verify absences of undeclared activities or anomalities in industrial or semi-industrial processes. A software tool has been developed upon request of the Euratom inspectorate to monitor in real time the nuclear material (NM) flow of about twice 850 tons/yr through the whole PUREX process in UP2 and UP3 for the spent fuel of power reactors at the La Hague site. The about 800 kg of Pu