Plutonium isotopic analysis of highly enriched mixed oxides

We investigated the analysis method used by the International Atomic Energy Agency (IAEA) to determine the plutonium isotopic composition of highly enriched mixed oxides (MOX). The IAEA currently uses the Cicero multichannel analyzer and the IAEAPU algorithm for its analysis. In our investigation the plutonium isotopic measurements were found to be good for PuO2 powder or low-enriched MOX, but acceptable for highly enriched MOX in IAEA special nuclear material (SNM) accountability applications. The gamma-ray interferences from 235U resulted in underestimation of the isotopic composition of 239Pu and overestimation of all other plutonium isotopes. Samples with high 240Pu content were found to have significantly higher error in plutonium isotopic analyses of highly enriched MOX. Code modifications or use of calibration curves are necessary for plutonium isotopic analyses of highly enriched MOX in IAEA SNM accountability applications