PLUTONIUM MASS MEASUREMENTS IN WASTE DRUM BY GAMMA SPECTROMETRY: PRINCIPLE AND RECENT IMPROVEMENTS

A technique developed at the “Institut de Radioprotection et de Sûreté Nucléaire” for measuring quantity of plutonium contained in waste drums is presented. The method is based on a gamma spectrometric acquisition device with a plutonium mass determination using the so called « infinite energy extrapolation method ». It uses several energy peaks of 239Pu and 241Pu ranging from 100 keV to 500 keV to evaluate the self-absorption correction of the plutonium in the drums. The gamma spectrometric acquisition may be completed by another input from a gamma scanning device in order to improve the final result. The two dedicated instruments and software have been developed to fulfill domestic safeguard inspection requirement: on-site measurement with transportable equipment. The paper addresses the two equipment explaining their principle. Other enhancements are discussed, like the spectra acquisition and analysis using automatic cumulative acquisition, and the possibility to perform analysis even with the presence of \"polluting\" elements that emit photons.