Year
2000
Abstract
The N95 is a high sensitivity passive neutron coincidence counter designed for high accuracy, high sensitivity plutonium assay. The 240Pu effective mass is determined by applying time correlation analysis to the neutron pulse stream using shift register electronics. It is suitable for routine safeguards applications as well as the analysis of waste material contaminated with plutonium. This paper describes the recent application of the N95 to waste monitoring as part of a glovebox decommissioning programme. Individual measured waste items will be removed from the glovebox, cleaned and packaged prior to assay using a pair of N95 units and subsequent consignment to 200 l waste drums. This permits a running total to be maintained for the total fissile content of 200 l waste drums using plant fingerprint data for the relative uranium / plutonium composition. This measurement strategy ensures that the upper fissile limit for waste drums is not breached. A set of calibration measurements has been made using eight simulated laboratory waste matrices with a diverse range of constituents, using a reference PuO2 sample placed at the centre. The measurements demonstrated the modest matrix dependence, with a standard deviation of only ? 4 % taken over all the matrices. While the design of the N95 ensures that both the matrix and the position dependence of the response are minimal, systematic uncertainties of this nature will be minimised when a large number of packages are placed into a 200 l drum.